More recent research, however, suggests that high school and college science teachers often emphasize laboratory procedures, leaving little time for discussion of how to plan an investigation or interpret its results (Tobin, 1987; see Chapter 4). Taken as a whole, the evidence indicates that typical laboratory work promotes only a few aspects of the full process of scientific reasoning—making observations and organizing, communicating, and interpreting data gathered from these observations. Typical laboratory experiences appear to have little effect on more complex aspects of scientific reasoning, such as the capacity to formulate research questions, design experiments, draw conclusions from observational data, and make inferences (Klopfer, 1990, cited in White, 1996).
Evidence from Research on Integrated Instructional Units
Research developing from studies of integrated instructional units indicates that laboratory experiences can play an important role in developing all aspects of scientific reasoning, including the more complex aspects, if the laboratory experiences are integrated with small group discussion, lectures, and other forms of science instruction. With carefully designed instruction that incorporates opportunities to conduct investigations and reflect on the results, students as young as 4th and 5th grade can develop sophisticated scientific thinking (Lehrer and Schauble, 2004; Metz, 2004). Kuhn and colleagues have shown that 5th graders can learn to experiment effectively, albeit in carefully controlled domains and with extended supervised practice (Kuhn, Schauble, and Garcia-Mila, 1992). Explicit instruction on the purposes of experiments appears necessary to help 6th grade students design them well (Schauble, Giaser, Duschl, Schulze, and John, 1995).These studies suggest that laboratory experiences must be carefully designed to support the development of scientific reasoning.
Given the difficulty most students have with reasoning scientifically, a number of instructional units have focused on this goal. Evidence from several studies indicates that, with the appropriate scaffolding provided in these units, students can successfully reason scientifically. They can learn to design experiments (Schauble et al., 1995; White and Frederiksen, 1998), make predictions (Friedler, Nachmias, and Linn, 1990), and interpret and explain data (Bell and Linn, 2000; Coleman, 1998; Hatano and Inagaki, 1991; Meyer and Woodruff, 1997; Millar, 1998; Rosebery, Warren, and Conant, 1992; Sandoval and Millwood, 2005). Engagement with these instructional units has been shown to improve students’ abilities to recognize discrepancies between predicted and observed outcomes (Friedler et al., 1990) and to design good experiments (Dunbar, 1993; Kuhn et al., 1992; Schauble et al., 1995; Schauble, Klopfer, and Raghavan, 1991).
The actual yield is the amount of product actually obtained in a given experiment. Normally,it is obtained by isolating the product of the reaction and weighing it.The percent yield is a measure of the efficiency of the reaction and is defined as:Actual experimental yield% yield = (100) theoretical yield“Actual yields” that is greater than “theoretical yields” usually imply an impure product. If theactual yield is less than the theoretical yield, it is usually because of incomplete reaction or side reactions or loss of product in one of the steps in the experiment.
Gas collection apparatus (Figure 5.1), 16 x 150 mm test tube, 1000-mL Florence flask, 1000-mL beaker
Baking soda, solid sodium hydrogen carbonates (NaHCO
A 16 x 150 mm dry test tube is weighted on the balance, and the mass is recorded.1-2 g of baking soda, NaHCO
, is added and reweigh accurately.
The apparatus is set up as shown in Figure 5.1. The Florence flask is filled to theneck with tap water, and the gas collection apparatus is inserted. The small rubber stopper is inserted into the test tube as shown.
The test tube is heating gently. The water being displace into the beaker is observedas carbon dioxide gas is produced. As the water level in the beaker increases, thetest tube is continuing heating with a gentle flame. After the water level remainsconstant for a couple of minutes, discontinue heating and the test tube is allowed tocool for 10 minutes.
The test tube containing the sodium carbonate residue is reweighted. The mass of Na
is found by subtracting the mass of the test tube and residue.
The theoretical yield of sodium carbonate, Na
, from the mass of pure bakingsoda that was heated is calculated. The percent yield of sodium carbonate iscalculated.