Pre-service chemistry teachers' competencies in the laboratory: a cross-grade study in solution preparation

Abstract

One of the prerequisites for chemistry teacher candidates is to demonstrate certain laboratory skills. This article aims to determine and discuss the competencies of pre-service chemistry teachers in a chemistry laboratory context working with solution chemistry content. The participants in this study consisted of a group of pre-service chemistry teachers in the first to fifth years of a chemistry teacher education program. The participants were given individual tasks of preparing solutions of a certain concentration. The tasks included two steps: calculation and application. The participants were also observed in terms of the degree to which they followed the laboratory safety rules. Overall, the pre-service teachers made numerous errors in calculating the correct amounts of a substance and preparing a solution, as well as obeying the safety rules. Interestingly, the participants' laboratory competencies showed a trend along their grade levels; namely, a slight increase and then a sharp decrease in their solution preparation knowledge and skills that could be associated with retention loss or decay over time in the absence of rehearsal and/or ill-encoding. These results may contribute to the discussion on virtual and physical laboratories in chemistry education.

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Introduction

The main field of investigation of chemistry involves atoms, ions, molecules, the interactions occuring between these entities and the forces that govern atomic and molecular levels. Therefore, topics in chemistry education include abstract atomic level or symbolic representations at both secondary and tertiary levels (Nakhleh, 1992; Ayas and Demirbaş, 1997). Even though there are few opponents (Hawkes, 2004), many claim that chemistry laboratories for chemistry education are crucial learning environments for the very abstract nature of chemistry topics (Singer et al., 2005; Zoller and Pushkin, 2007). Inquiry based teaching has been addressed by the US and other nations' calls for reform in science education and has been placed as a major goal for science education standards (NAP, 2013). The chemistry laboratory has been proposed as one of the main components of inquiry-based teaching. In essence, students can act as researchers in laboratories and learn science process skills by naturally observing, measuring, inferring, controlling variables, experimenting, etc. (Basağa et al., 1994). Laboratories in chemistry education are considered to have potential as a crucial medium not only for improving science process skills, but also for improving conceptual understanding by making abstract subjects more concrete and visual (Ayas et al., 1994; Bybee, 2000; Laredo, 2013). Similarly Hofstein and Lunetta (2004) noted that the primary emphasis of laboratories should not be limited to learning certain scientific methods or laboratory techniques, but rather laboratories should allow students to investigate phenomena by using the methods and procedures of science thereby enabling them to solve problems. Research in this domain has also pointed out that laboratory activities may positively affect students' attitudes and interests toward chemistry (Cooper and Kerns, 2006; Karataş et al., 2015a; Lang et al., 2005; Okebukola, 1986). Moreover, the National Research Council (NRC) report also addressed a few goals of laboratory experience including developing scientific reasoning; realizing the complexity and ambiguity of empirical work; having a more contemporary view of the nature of science; and developing collaborative skills (Singer et al., 2005).

Even though there are numerous benefits of having laboratory experience, various shortcomings have been identified in reference to laboratory work in chemistry education. As Koretsky et al. (2009) stated, laboratories are resource-intensive, both in terms of acquiring and maintaining equipment and in terms of staffing requirements. Because of these constraints, laboratories might not meet their initial goals (Koretsky et al., 2011). In particular, the competency of laboratory staff is a very important aspect of laboratory experience (Singer et al., 2005). As Cooper and Kerns (2006) noted, a chemistry laboratory can be a valuable learning environment only when the instructor understands the purpose of the laboratory experience well and teaches accordingly.

Several studies have reported that teachers do not utilize laboratories for many reasons, but mainly because of lack of knowledge and laboratory skills (Ayas et al., 1993; Nakiboglu and Sarıkaya, 1999; Singer et al., 2005). There are mainly two different ways of improving the laboratory skills of science and especially chemistry teachers: in-service and pre-service training. Training chemistry teachers with an in-service laboratory program may not be feasible because a long period of time is required to improve motor skills as compared to improving cognitive skills. It is therefore difficult to find teachers who would commit to spending at least a few months to improve their laboratory skills. Pre-service training is the best way of ensuring that future chemistry teachers are competent and know how to deal with the laboratory experience and experiments. The first step of this attempt would be to identify and determine the current competence level of pre-service chemistry teachers. Only a limited number of studies have investigated pre-service chemistry teachers' competencies in the laboratory. Research with pre-service science and chemistry teachers has demonstrated that their chemistry laboratory skills are very limited and are far from being at an acceptable level of competence (Coştu et al., 2005). Coştu and his colleagues (2005), however, conducted their study just after the participants completed their general chemistry laboratory course work. So, this does not provide a general picture of graduating pre-service teachers' laboratory competencies. Their findings are not useful for understanding how pre-service chemistry teachers' education improves their laboratory skills along the way either. Thus, identifying pre-service chemistry teachers' competencies in the laboratory from their first year to graduation would shed light on the development of their laboratory skills as well as the efficiency of the teacher training program. Therefore, this study intended to examine these issues to contribute to chemistry education research literature. These issues were examined in the context of solution chemistry as it is the basic and pre-requisite content of chemistry and the chemistry laboratory (Çalık et al., 2007, 2009; de Berg, 2012).

This study also addressed the recent call from Towns (2013) regarding the future of chemical education research (CER) when she noted “As a starting point, the field needs studies that build an understanding of what learning outcomes – cognitive, psychomotor, and affective – can be achieved and assessed in the laboratory across the curriculum” (p. 1108). By focusing on pre-service chemistry teachers' solution preparation competences along their education, this study addresses both the cognitive and psychomotor learning outcomes of laboratories and their prolonged effects. In addition, few cross-age studies have been conducted on laboratory competency and this study will seek to address a gap among these studies. Thus, the purpose of this study is to examine pre-service chemistry teachers' laboratory competences in the case of solution preparation across the grades. The guiding research questions for this study were as follows:

• What are pre-service chemistry teachers' competence levels in preparing a solution at a certain concentration?

• How do the pre-service chemistry teachers' competence levels change over the course of the school year?

Methodology

Design of the study

As the main purpose of the present study was to investigate the participants' competence levels for certain laboratory skills and then compare them across grades, the methodology employed in this study required both quantitative and qualitative approaches in a descriptive manner. In the process, data were collected via open-ended questions and structured observations and were analyzed separately. Then, the results were merged to support each other and to increase the understanding of the situation, this process can be referred as triangulation (Johnson and Christensen, 2012).

Setting and participants

The study was conducted with pre-service chemistry teachers in Turkey. The training of pre-service chemistry teachers is an integrated five-year long program in Turkey. During the program, pre-service chemistry teachers take courses in chemistry and pedagogy, as well as general education courses; the pedagogy courses are spread throughout the program with the exception of the first year. The first year program includes more general courses such as calculus, physics, oral and written communication, and so on. There are no chemistry and/or chemistry laboratory courses in the fifth-year program. The fifth-year program consists of practicum, student counselling, discipline-specific educational research, and elective chemistry education courses (e.g. teaching chemistry concepts; ICT in chemistry education; chemistry textbook analysis and evaluation; etc.). Pre-service chemistry teachers are required to attend several laboratory sessions from the first year to the fourth year including general chemistry laboratory I and II (fall and spring semesters of the first year); analytical chemistry laboratory I and II and inorganic chemistry laboratory I and II (fall and spring semesters of the second year); physical chemistry laboratory I and II and organic chemistry laboratory (fall and spring semesters of the third year); and biochemistry laboratory in the fall semester of the fourth year (for detailed course work see URL-1).

This study took place at a large university located in North East of Turkey. Approximately 40 pre-service teachers were enrolled in each year of the five-year chemistry teacher preparation programme. The participants were recruited just before a class by asking them to provide their e-mail addresses if they were willing to participate in the study after the purpose and the process of the study was briefly explained in the absence of the instructor. As seen in Table 1, the participants of the study were 88 volunteered pre-service chemistry teachers from different grades. Among these participants six pre-service chemistry teachers from each grade were chosen to further investigate their laboratory competence by employing two solution preparation tasks. During the tasks they were observed and briefly interviewed (if there was an ambiguity) about what they are doing. The participants for observation/interview were primarily chosen based on their responses to a test about solution calculation, as being low, moderate and high, by sending another e-mail to the address that they provided. In this way, it was believed that a general idea could be drawn regarding the class competence level.

Table 1 The participants of the study

Data collection	Number of participants in each grade
	Year 1	Year 2	Year 3	Year 4	Year 5	Total
Solution preparation test	24	21	19	17	14	88
Observation/interview	6	6	6	6	6	30

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Data collection

A solution preparation test (SPT) comprising five open-ended items (see Appendix 1) and a solution preparation observation form (SPOF) were utilized in order to collect data about the pre-service chemistry teachers' competence levels regarding solution preparation and laboratory safety precautions (see Appendix 2).

The SPT consisted of five open-ended problems about the preparation of solutions using different chemicals (e.g. NH₃, Kr₂Cr₂O₄, aqua regia, etc.) and various concentrations types including percentage of liquid and solid solute, molarity, normality, and molality. The questions were adapted from those of Coştu et al. (2005) and further refined with the help of a panel of researchers including two chemists, two chemistry educators and one linguistic expert. For example, questions were written in a more passive voice if they were active questions. A pilot study was carried out, after experts' edits and suggestions were fulfilled, with 20 pre-service science teachers who were trained to teach from grade 5 to 8. Based on the pilot study the questions were further revised and refined to clarify their meaning and expression. The pilot study helped to revise the rubrics that were used in the analysis.

The SPOF was a structured observation form comprising 25 items in three sections including equipment usage competency, solution preparation competency, and laboratory safety competency. For each observable behaviour the participants could chose from one of three options: Right; Partly Right, and, Wrong or Not Observed. The SPOF on the topic of solid–liquid and liquid–liquid solution preparation was developed by a panel of experts consisting of two chemists and two chemistry educators. The participants were asked to complete two tasks: the preparation of a 3 N 250 ml H₂SO₄ solution from stock solution and the preparation of a 2 M 100 ml NaOH solution. It should be noted that the participants were given pseudo compounds for safety precautions: tap water instead of H₂SO₄ and granulated salt instead of NaOH.

Procedure

As discussed by Winberg and Berg (2007), in the majority of traditional laboratories pre-experiment assignments are set for the students to complete before the practical work is carried out. Usually, these assignments include questions which require a calculation similar to the one required in their final reports. Questions might also be asked about the purpose of specific steps of the experimental procedure. In this study, a similar procedure was followed. Before, the students prepared solutions of specified concentrations (e.g. molar, molal, and normal), all of the participants were given the open-ended test which included five questions. The participants were asked to solve each problem in the test. After these tests were analyzed, six participants were chosen based on their scores in the test. For each grade, two low, moderate, and high scorers were selected after assessing their solution preparation performance in the laboratory. In the laboratory, every participant was observed individually while they were asked to prepare two solutions; one normal (liquid–liquid) and one molal (liquid–solid). The necessary chemicals and chemical equipment (glassware, apparatus, and tools) as well as safety equipment (goggle and apron) were provided. Specifically different types and sizes of glassware were put on the tables in order to see what the students chose if they were presented with various options. For example, the participants were asked to prepare 250 ml of 3 N H₂SO₄ solution. They were provided with three different volumetric flasks of three different volumes including 100 ml, 250 ml, and 500 ml. They were also provided with graduated cylinders, Erlenmeyer flasks, and beakers of different sizes. The participants were expected to pick the one which was the most accurate and best designed for the job, in other words, a 250 ml volumetric flask. While the participants were performing the task, the SPOF was filled and they were asked to talk-out-loud about what they were doing and why they were doing it. The aim of this procedure was to leave no room for hesitation between what was observed and what was interpreted.

Ethical considerations

Chemical education research is unique because human subjects might come across physical, mental, and social concerns. This study complies with the RSC's ethical guidance to researchers (Taber, 2014). First of all, all of the participants volunteered for the study. The purpose and process of the study, the responsibilities, as well as the possible benefits and risks to the participants were explained to the participants. An agreement between the participants and the researcher guaranteed the privacy of the participants. Laboratory activities require safety precautions to be implemented while experiments are conducted. In this study, two solution preparation tasks were carried out by the participants. The preparation of the solutions involved the use of chemicals and glassware but no other chemical processes (heating, evaporating, distilling, etc.). The participants were asked to prepare acid and base solutions, but tap water and granulated rock salt were provided as pseudo compounds. In other words, the chemicals that were used for the study are not hazardous. Thus, the potential health risk for the participants was not greater than that of preparing a glass of lemonade.

Data analysis

To ensure that the data analysis was credible, a rubric, presented in Table 2, was developed for the problems in the test. Similarly another rubric (as seen in Table 2) was developed for solution preparation while developing the SPOF by taking into account potential problems: appropriate laboratory equipment usage, laboratory safety, and solution preparation.

Table 2 The rubric for the analysis of the SPT and SPOF problems

Theme	Category	Grading criteria for SPT	P
Solution problem	Correct	Demonstrating the right solution and correct result	2
	Partly correct	Demonstrating the right solution, but an incorrect unit of conversion and calculations or one or more missteps for the solution	1
	Wrong or N/R	Wrong solutions, non-filled items or “I do not know,” “I have no idea” types of responses	0

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Theme	Category	Grading criteria for SPOF	P
Laboratory equipment usage	Right	Using the right equipment appropriately	2
	Partly Right	Not using some of the required equipment or misusing the right equipment	1
	Wrong or N/O	Not using the required equipment or using the equipment incorrectly	0
Solution preparation	Right	Solving the problem correctly and using the right laboratory equipment correctly or partially correctly (or one wrong)	2
	Partly right	Solving the problem correctly, but not using the right equipment properly Not solving the problem correctly, but using the right equipment properly	1
	Wrong	Not solving the problem and not using the right equipment properly	0
Laboratory safety	Right	Taking into account all of the safety measures identified in the SPOF	2
	Partly right	Taking into account three or more safety measures identified in the SPOF	1
	Wrong	Taking into account two or fewer safety measures identified in the SPOF	0

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The rubric was developed based on the descriptions defined by Coştu et al. (2005) and the guidelines provided by Mertler (2001). The rubric was used while observing the participants performing the solution preparation task. As for the development of the SPT and the SPOF, a panel of experts consisting of two chemists and two chemistry educators acted as advisors for the development of the rubric.

Results

Results from SPT

The collected data were analyzed based on the rubric in Table 2. The results from these analyses were presented accordingly. Descriptive results from the paper-pencil test about solution problems are presented and a comparison of the grades is provided.

As seen in Table 3, the first question in which the participants were asked to prepare a dilute molar solution from a higher concentration of NH₃(aq) solution was responded to with the most correct answers. On the other hand, the fifth question in which the participants were asked to prepare a 0.02 molal K₂Cr₂O₄(aq) solution was responded to with the most wrong answers. The first question was answered most correctly by all the grade levels, except for the fifth-years. Only 50% of the fifth-years answered the first question correctly and interestingly almost all of the fifth-years gave the right answer to the third question which they were asked to prepare aqua regia. Preparing a 3 N solution from a polyprotic acid (H₃PO₄) was responded to least correctly: only 27% of the participants' responses were correct and 28% of them gave partly correct answers.

Table 3 The pre-service chemistry teachers' answers to solution problems

Grades	N	The pre-service chemistry teachers' responses
		Q1 (%)			Q2 (%)			Q3 (%)			Q4 (%)			Q5 (%)
		C	P	N	C	P	N	C	P	N	C	P	N	C	P	N
C: correct; P: partly correct; N: wrong or no response.
First-year	24	96	4	—	67	8	21	29	—	71	25	46	29	46	—	54
Second-year	14	71	22	7	43	14	43	64	—	36	7	7	86	36	7	57
Third-year	19	90	5	5	26	26	48	48	5	47	26	53	21	42	26	32
Fourth-year	17	88	—	12	47	6	47	88	—	12	41	12	47	76	—	24
Fifth-year	14	50	14	36	29	—	71	93	—	7	36	21	43	21	—	79
Average	18	79	9	12	42	11	47	64	1	35	27	28	45	44	7	49

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The average score for the whole sample was calculated as 5.83 out of 10, with a standard deviation of 2.33, which indicates that there was a wide-range of responses. When comparing the pre-service teachers' grades, the fourth-year pre-service teachers' mean score was the highest and the second-year pre-service teachers' was the lowest as seen in Table 4. When ANOVA was run for the test scores presented in Table 4 to compare the effects of years of official training to the answers of solution problems, significant differences were found at the p < 0.05 level between the participants' school years and their test scores, both total and itemized, with one exception [F_Total(4, 83) = 3.38, p = 0.013; F_Q1 = 4.52; F_Q3 = 8.50, p = 0.000; F_Q4 = 2.92, p = 0.026; F_Q5 = 5.28, p = 0.001]. There was no significant difference between the school years and the second item of the test which was about the preparation of a solution based on mass percentage [F_Q2(4, 83) = 2.23, p = 0.072].

Table 4 The pre-service chemistry teachers' means for solution problem scores

Grades	The participants' mean scores from the test items
	Q1		Q2		Q3		Q4		Q5		Total
	M	Sd	M	Sd	M	Sd	M	Sd	M	Sd	M	Sd
First-year	1.93	0.20	1.42	0.88	0.58	0.93	1.00	0.78	0.92	1.02	5.88	2.05
Second-year	1.64	0.63	1.00	0.96	1.29	0.99	0.21	0.58	0.64	0.93	4.79	2.08
Third-year	1.84	0.50	0.79	0.86	1.00	1.00	1.11	0.74	1.11	0.88	5.84	2.34
Fourth-year	1.76	0.66	1.00	1.00	1.88	0.49	0.94	0.97	1.76	0.67	7.35	2.23
Fifth-year	1.14	0.95	0.57	0.94	1.86	0.54	0.93	0.92	0.43	0.85	4.93	2.40
Average	1.73	0.64	1.00	0.95	1.24	0.97	0.88	0.84	1.00	0.97	5.83	2.33

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As seen in Table 5, post hoc comparisons using the Tukey HSD test indicated that the mean score of the whole test for second-years (M = 4.79, Sd = 2.08) was significantly different from that of the fourth-years (M = 7.35, Sd = 2.23) and was in favour of the fourth-years. Similarly, the mean score of the whole test for the fourth-years was significantly different from that of the fifth-years (M = 4.93, Sd = 2.40) and was in favour of the fourth-years. Post hoc comparisons were also utilized for each item of the test.

Table 5 Significant Tukey test results at p < 0.05 level

Grades	Second-year	Third-year	Fourth-year	Fifth-year
First-year	Q4 (1st year)		Q3 (4th year) Q5 (4th year)	Q1 (1st year) Q3 (5th year)
Second-year		Q4 (3rd year)	Total (4th year) Q5 (4th year)
Third-year			Q3 (4th year)	Q1 (3rd year) Q3 (5th year)
Fourth-year				Total (4th year) Q1 (4th year) Q5 (4th year)

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No significant difference was found between the grades for question two (Q2) which asked the participants to prepare a solution in percent composition by mass. The Tukey HSD test indicated that the mean score of Question 1 (Q1) for the fifth-years (M = 1.14, Sd = 0.95) was significantly different to that for the first-years (M = 1.93, Sd = 0.20), third-years (M = 1.84, Sd = 0.50), and fourth-years (M = 1.76, Sd = 0.66). For Question 3 (Q3), the mean scores for the first-years (M = 0.58, Sd = 0.93) and third-years (M = 1.00, Sd = 1.00) were significantly different from those of the fourth-years (M = 1.88, Sd = 0.49) and fifth-years (M = 1.86, Sd = 0.54). For Question 4 (Q4), the mean scores for the second-years (M = 0.21, Sd = 0.58) was significantly different from those of the first-years (M = 1.00, Sd = 0.78) and third-years (M = 1.11, Sd = 0.74). When the students' scores were compared for Question 5 (Q5), the mean scores for the fourth-years (M = 1.76, Sd = 0.67) was significantly different from those of the first-years (M = 0.92, Sd = 1.02), second-years (M = 0.64, Sd = 0.93) and fifth-years (M = 0.43, Sd = 0.85).

Results from the solution preparation in the laboratory

The participants' solution preparation was analysed in three main categories based on the SPOF and the think-aloud interview protocol: solution preparation, laboratory safety, and equipment usage for liquid–liquid and liquid–solid solutions. As can be seen from the results presented in Table 6, a few of the participants lacked the necessary skills and more than half of the participants could not show or perform necessary behaviours correctly. The participants generally had deficiencies in laboratory safety precautions. Only four out of the thirty participants took into account all of the laboratory safety codes listed in the SPOF. The majority of the participants partially obeyed the safety codes for both solid–liquid and liquid–liquid solutions. Many participants did not wear goggles while preparing solutions.

Table 6 Categorized results from the SPOF

Themes	Grades	Behaviour
		Liquid–liquid				Solid–liquid
		R	PR	W	X	R	PR	W	X
R: right, PR: partly right, W: wrong or no response, X: calculated mean score based on rubric in Table 2.
Laboratory equipment usage	1st year	2	3	1	1.17	4	2	—	1.67
	2nd year	3	3	—	1.50	6	—	—	2.00
	3rd year	5	1	—	1.83	1	3	1	0.83
	4th year	3	3	—	1.50	5	1	—	1.83
	5th year	2	4	—	1.33	3	2	1	1.33
	Total	15	14	1	1.47	19	8	2	1.50
Solution preparation	1st year	3	3	—	1.50	3	3	—	1.50
	2nd year	3	—	3	1.00	3	3	—	1.50
	3rd year	3	3	—	1.50	4	2	—	1.67
	4th year	3	3	—	1.50	4	2	—	1.67
	5th year	1	5	—	1.17	1	1	4	0.50
	Total	13	14	3	1.33	15	11	4	1.37
Laboratory safety	1st year	1	4	1	1.00	1	4	1	1.00
	2nd year	1	4	1	1.00	1	4	1	1.00
	3rd year	—	6	—	1.00	—	6	—	1.00
	4th year	2	4	—	1.33	2	4	—	1.33
	5th year	—	5	1	0.83	—	6	—	1.00
	Total	4	23	3	1.00	4	24	2	1.07

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For each category, the participants' average scores by grade were calculated and are illustrated in Table 6. As a three-point scale rubric (see Table 2) was utilized, the average scores were categorized as poor for 0 to 0.66, moderate for 0.67 to 1.33 and good for 1.34 and over. When the three main categories were considered, the score for obeying the laboratory safety regulations was the lowest of all, but was at a moderate level. The participants' overall equipment usage and solution preparation skills were considered to be good with the exception of the liquid–liquid solution preparation skills. When each school year was examined, on the other hand, only the fifth-year pre-service chemistry teachers' solid–liquid solution preparation was considered to be poor. The remaining participants achieved moderate or good scores.

In order to illustrate the change in the pre-service chemistry teachers' chemistry laboratory competencies, a line chart was drawn for each theme. As seen in Fig. 1, when the participants prepared a liquid–liquid solution, they all showed lower equipment usage skills than for the preparation of a liquid–solid solution except for the third-year participants. The third-year participants' equipment usage skills did not follow the general trend as they performed well for liquid–liquid solutions, but not that well for the preparation of liquid–solid solutions. Most of the wrong usage resulted from not measuring the volume precisely, not choosing an appropriate size of volumetric flask or not using one at all. Another common mistake took place when the participants tried to weigh the solid. A few of them did not use a spatula to take the solid from its container, they poured it directly into a beaker/paper then refilled the extra substance into the container.

Fig. 1 Laboratory equipment usage by school year.

Fig. 2 illustrates the solution preparation skills of the pre-service chemistry teachers. There was a slight increase in the preparation skills as the years of education increased except for the fifth-year. As can be seen from Fig. 2, the liquid–liquid and liquid–solid solution preparation skills of the fifth year pre-service chemistry teachers' decreased compared to those of the other participants.

Fig. 2 Solution preparation skills by school year.

Another category that was examined via the SPOF was laboratory safety. The participants achieved the lowest average scores for this category. As can seen from Fig. 3, there was no difference between the solution types for the participants except for the fifth-years. Even though for the fourth-years there was an increase in the following of laboratory safety regulations, a rapid decrease was observed from the fourth-year to the fifth-year. More than half of the participants (N = 17) did not wear goggles while conducting their duties. This was the most common violation against laboratory safety regulations. Another safety precaution that was not taken into account by 30% of the participants (N = 9) was not using an appropriate place to conduct experiments including not using a fume hood. Even though half of the participants had long hair, one third of them did not use a hair clip to tie their hair back which was the third most common violation.

Fig. 3 Laboratory safety precautions by school year.

Discussions and conclusions

The purpose of this study was to determine and compare pre-service chemistry teachers' laboratory competences in the case of solution preparation. The participants' laboratory competencies were examined in two sequential stages; theoretical and practical. The participants' overall problem solving skills to prepare a solution of a certain concentration was moderate (average score is 5.83 out of 10; see Tables 4 and 6). But, their average scores for calculating the right amount of solute varied based on the solution and the concentration type. The highest average score was 1.73 out of 2 which was achieved for the preparation of a dilute molar solution from a higher concentration of NH₃(aq). The participants generally used a common equation for molarity which is located in textbooks for their calculations. When a similar question was asked to prepare a 3 N phosphoric acid solution, most of them stuck with below average scores. First, they calculated the molarity of the stock solution of phosphoric acid. Then, they tried to convert it to normality. Most of the participants who solved the first problem were successful at the first stage, but they failed while converting molarity to normality as they either did not take into account equivalency or miscalculated it (Coştu et al., 2005). This would be as a consequence of not using normality solutions as often as molarity solutions in their laboratory classes. The participants' responses for normality question were interesting in another way. As can be seen from the results presented in Table 3, only 12% of the participants' responses to the first questions were either wrong or unrelated, but 45% of the responses for the fourth question fitted into this category. This may be the result of not being aware of the relationship between molarity and normality concentrations or believing that the normality is harder topic. It is believed that the second option is more probable because adding the correct and partly correct responses to the normality question gives 55% of the total responses. If the participants calculated molarity of the stock acid solution before converting it to normality, they would have taken partial credit. This means that they did not even try it or that they tried it in a different way as they thought that it is hard to solve. As Karataş et al. (2015b) indicated, beliefs might be one of the main factors that affect learning. Similarly, self-efficacy is claimed to play a major role in academic achievement as this may have also impaired the participants' ability to solve the normality problem (Bandura et al., 1996).

In addition to the problems on normality, the number of correct responses to the questions on molality and percent composition (by mass) were below 50%, which is considered as quite low. This indicates that the pre-service chemistry teachers did not comprehend the solution chemistry well. When viewed from a developmental perspective, there is no clear indication of comprehension through school years. Regardless, a significant difference was found between the second-years and the fourth-years as well as the fourth-years and fifth-years (see Tables 4 and 5). The fifth-year pre-service teachers' average score from the test was 4.93 out of 10 which is the second worst after the second-years. The same trend was also apparent for solution preparation in the laboratory, that is the fifth-year participants' problem solving skills were worse than those of the rest of the participants (see Fig. 2). The fifth-year program does not have any chemistry or chemistry laboratory courses (see URL-1). Therefore, lower scores for solving concentration problems could stem from the absence of chemistry courses. On the other hand, the fourth-year program is very active in terms of chemistry as well as chemistry education courses. The pre-service chemistry teachers took methods, instructional technology and material design courses which require developing and employing teaching materials and models based on chemistry topics. In this sense, although it is claimed that active participation may enhance learning permanency, our findings somewhat contradict this prediction, as the fifth-year participants' problem solving skills were significantly lower than the fourth-years. Research in retention implies that in the absence of retrieval practice, recalling information simply decays over time as a result of memory trace loss (Wixted, 2004; Roediger and Butler, 2011). Atkinson–Shiffrin's dual store model of memory suggests that the longer an item stays in the short-term memory, the stronger its association becomes in the long-term memory (Atkinson and Shiffrin, 1968). These two claims imply that maintenance rehearsal including several recalls and retrievals/reminders of memory would be necessary to preserve long term memories (Wixted, 2004). In addition, a well-organized encoding process in the short-term memory might help retention from the long-term memory, an ill-organized (dissociated or confused confrontation) encoding might cause the opposite effect (Ruchkin et al., 2003). Open-ended tasks and active participation – which involve episodic and autobiographic memory – also help encoding and retention (Arthur et al., 1998). Thus, the nature of the chemistry laboratory class should have a great effect on retention or forgetting. Chemistry laboratory classes for the pre-service teachers are generally performed in large groups. Each class member is unlikely to get a chance to prepare chemical solutions. The nature of experiments and laboratory manuals which look like cookery-book recipes where students simply follow the instructions without understanding the concepts and processes could be the reason for the fast memory decay of the participants (Gallet, 1998).

The pre-service chemistry teachers made mistakes especially while calculating and converting the units. Even though these mistakes seem technical not chemical, they still affect how the teachers prepared the solutions because a solution of the wrong/unknown concentration may cause unexpected results in a laboratory class even though the solutions were not prepared for research. This might affect the sensitivity of the experiments including the rate of reaction, equilibrium constant, titration, and so on. Another mistake that can affect the sensitivity of the results obtained took place when the participants were measuring the liquid level as a few of the participants read the top of the concave meniscus instead of the bottom. This is very basic knowledge about observation, but a few of the participants did not seem to be aware of it or to care about it (Coştu et al., 2005). The members of the laboratory class were generally expected to read and understand related parts of the laboratory manual before conducting experiments. What happened was a little different from what was expected. Thus, ICT based pre-laboratory exercises that aim at the aforementioned aspects would be an effective way of avoiding such simple mistakes (Chittleborough et al., 2007).

Laboratory equipment usage was also examined while the participants were carrying out the given tasks of preparing liquid–liquid and solid–liquid solutions. Generally the equipment usage was right or partly right. One of the major mistakes was not using the right equipment for the task; this included the use of a volumetric flask and a spatula. A few participants used a graduated cylinder for the preparation of a solution. Since only a few participants made this mistake, it is believed that they were not aware of the reason for using a volumetric flask other than it is a common way of solution preparation that happens in their laboratory classes. On the other hand, the reason they used a graduated cylinder may stem from their practical usage habits, as a graduated cylinder can be used to measure liquids when no precise measurement is needed. In addition, a few of the participants did not use a spatula while taking solid chemicals from the containers. This is also very basic knowledge and it may be even considered to be common sense that does not require training. As in the case of using a graduated cylinder instead of a volumetric flask, pouring directly from the container seemed to be more practical for the participants. Thus, it was inferred that laboratory work may force the participants to make decisions to develop new skills that are more practical for them, but may not be suitable for the chemistry laboratory. These laboratory behaviours could be explained by the expected utility theory (Briggs, 2014). The expected utility of an act is a weighted average of the utilities of each of its possible outcomes, where the utility of an outcome measures the extent to which that outcome is preferred. Thus, the higher the expected utility, the more likely the act to be chosen. In our case, the more practical usage of equipment might be perceived to be more utilitarian (Lengwiler, 2009).

In addition to these observations, a similar trend was observed when laboratory safety was considered. Many participants neither wore goggles nor tied their hair back, and did not take into account acid spatters. These observations might also be explained by the expected utility theory. More than half of the participants did not wear goggles which means that they did not consider it to be a necessary act to protect their eyes as the probability of having such an accident is very low, but wearing a goggle is irritating (a general student complain). This highlights the flaws in their risk analysis.

As with every other study, the present investigation has certain limitations. In this study, pre-service chemistry teachers' laboratory skills were examined across years. There were several variables that directly or indirectly affected the results that either could not be identified or controlled. Some of the limitations came from the research method that was chosen to investigate the participants' laboratory skills in a developmental manner. As different student cohorts were chosen for different school years, they had different backgrounds. They had, for example, different instructors for each class. As a social group, they might have had a micro-culture such as being a hard-working class or a lazy class. So, these and similar circumstances might have played a role over the results. However, the two phase approach should have addressed some of these limitations as in the second phase good, moderate and bad achievers were chosen to illustrate a general view. Regardless, there were many variables which were not possible to control. Thus, a longitudinal approach may be adopted to overcome some of these limitations in future studies.

Implications for teaching and teacher training

Although the chemistry laboratory is believed to be a part of chemistry learning and is a routine part of the chemistry curriculum, student learning in the laboratory has not been examined sufficiently (Towns, 2013). As a starting point, this study responded to the call to build an understanding of what learning outcomes, including, cognitive, psychomotor, and affective, can be achieved and assessed in the laboratory across a curriculum. It appears that the more chemistry laboratory courses are taken, the better the understanding of solution chemistry. However, the prolonged effects of a chemistry teacher training program gave mixed results. It seems that the fifth-year program does not support the participants' cognitive and psychomotor chemistry development as it focuses on more practicum and other educational courses. As a decrease was observed not only in the problem solving stage, but also in the safety and laboratory equipment usage stages, traditional teaching should be reconsidered. Thus, more chemistry applications should be integrated into teachers’ training programs even while they focus on more pedagogical aspects. As the students were found to perform better at certain solution problems in certain grades, this indicates that their education at that grade level should be related to those solution types. Thus, it is suggested that more computer and/or mobile technology assistance and other opportunities should be considered to help students retain what they have learned from their classes and laboratories. As Lunetta et al. (2007) suggested, well planned laboratory and simulation experiences should put students into an inquiring environment where students should be active not only “hands-on” but also “minds-on.” Research in learning and retention also suggests that well-encoding and rehearsals should slow down retention loss (Cowan, 2008). Moreover, laboratory activities should be part of the pedagogical content knowledge (PCK) packages of methods courses. Instead of just focusing on laboratory types and approaches in teaching, they should be employed to be a good illustration as well.

The participants gained the lowest scores for the safety aspect of the study. Safety elements included proper clothing, cleaning and waste disposal as well as special handling. For example, many participants did not wear goggles properly or did not wear them at all while they were preparing the acid–base solutions. There was no restriction or authoritarian guidance regarding safety precautions for research purposes. It seems that they were not aware of the risks. So, it is a humble prediction that they would not pay attention to safety issues greatly while teaching. Thus, while teaching laboratory safety, focus should have been to affective learning outcomes in accordance with rational or cognitive ones (Taber, 2015).

It looks like the pre-service chemistry teachers had conceptual issues regarding solution preparation, in addition, some of the issues were not conceptual but were psychological as was the case for the normality problem. The participants solved the molarity problem properly and they knew about normality by definition, but they could not solve the normality problem. Many of them could not get a partial credit for the problem as they did not attempt to solve it. It seems that they did not believe that they were able to solve the problem. So, their self-efficacy level was considered to be low for certain solution problems. Positive and successful attempts would raise self-efficacy in a certain field. Therefore, more instruction hours should be allocated to these students so that they can go over the concepts and solve related problems to increase their mastery of a topic. In most cases, standard solutions are provided by laboratory assistants and/or technicians. As students or pre-service teachers may not have a chance to calculate and prepare a solution, their experience could be limited to a “vicarious” level. As Reid and Shah (2007) asserted, the nature of the chemistry laboratory should be reconsidered. Students should be allowed – under guidance and control of the teaching assistants – to prepare their own solutions for the experiment. This increases their chemistry laboratory as well as chemistry conceptions competence level. This would affect the students' self-efficacy in a positive way as well.

This study employed a cross-grade approach to examine solution preparation skills of pre-service chemistry teachers. Developmental studies are crucial to evaluate and improve a programme. But, as discussed, this approach brings about many limitations as well. Thus, a longitudinal study approach should be taken into account to address these limitations to better understand how the laboratory could affect learning and retention. In addition to this study, a shorter (a semester long) but deeper investigation involving group/team work and a virtual laboratory should be considered while designing a new study to explore the laboratory effect. Another suggestion for researchers who are interested in laboratory work would be to focus on the problem solving stage of solutions. A think-aloud protocol was a useful tool for this study to confirm the observed behaviour. But, this study did not intend to examine the problem solving strategies and models of the participants. Further research might be fruitful to illuminate this area as it is the key area for chemists and chemistry teaching.

Appendix 1: solution preparation test (SPT)

Q1. How much NH₃ stock solution with d = 0.9 g cm⁻³ density and 10% by mass is needed to prepare 100 ml of 0.2 M NH₃ solution? (N: 14 g mol⁻¹ and H: 1 g mol⁻¹)

Q2. In order to prepare 150 ml of a 10% by mass KHSO₄ solution, how many grams of KHSO₄ are needed? (For solution d = 1.04 g cm⁻³, K: 39 g mol⁻¹, S: 32 g mol⁻¹, O: 16 g mol⁻¹, H: 1 g mol⁻¹)

Q3. Agua-regia should be prepared in 3 : 1 ratio of HNO₃ : HCl. According to this information how could you prepare 90 ml of aqua-regia? (O: 16 g mol⁻¹, N: 14 g mol⁻¹, Cl: 35.5 g mol⁻¹)

Q4. How much H₃PO₄ stock solution with d = 1.70 g cm⁻³ and 85% by mass is needed to prepare 200 ml of 3 N H₃PO₄? (P: 31 g mol⁻¹, O: 16 g mol⁻¹, H: 1 g mol⁻¹)

Q5. How many grams of K₂Cr₂O₄ are needed to prepare 0.02 m (molal) solution in 100 g of water? (K: 39 g mol⁻¹, Cr: 52 g mol⁻¹, O: 16 g mol⁻¹)

Appendix 2: solution preparation observation form (SPOF)

	Liquid–liquid			Solid–liquid
	R	PR	W	R	PR	W
Laboratory equipment usage
Solution container (volumetric flask [250 ml for the first one and 100 ml for the second one])
Propipetter
Pipette
Pure water washing bottle
Spatula
Solution preparation skills
Did s/he solve the problem?
Did s/he check the cleanness of the equipment?
Did s/he get certain amount from the stock solution in a beaker then using from there in order to protect purity of the stock solution?
Can s/he use pipette and propipetter properly while taking liquid?
Did s/he use pure water or tap water as solvent?
Can s/he measure the right amount for the liquid (concave, convex)?
Did s/he take into account the order of mixing the chemicals with the water? (For H2SO4)
Did s/he fill up the solution (container/volumetric flask) with the solvent? (For H2SO4)
Did s/he use the digital scale properly?
Did s/he check the tare of the glass before measuring the amount of chemical (for solids)
Did s/he add up to 100 ml of solvent to prepare solution?
Did s/he use the right equipment to take solid chemicals from the stock?
Did s/he dissolve the solid before adding water to complete the solution?
Laboratory safety precautions
Did s/he wear an apron?
Did s/he wear goggles?
Did s/he use a fume hood?
Was s/he aware that s/he needs to protect her/his eyes when opening a lid?
Did the participants with long hair tie their hair back?
Did s/he behave carefully for splitting?
Was s/he aware that no food and beverages are allowed in a laboratory?

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