ACT Science Mastery Lesson 13

ACT Science Mastery Lesson 13

Drawing Conclusions

Passage

Several recent health studies point to excessive sodium intake as a contributing factor to Various health problems. Sodium is typically added to food in the form of table salt (NaCl). Students performed two experiments to measure the sodium levels of various canned goods. 

Experiment 1

Four solutions, each containing a different amount of dissolved NaCl (table salt) were pre pared in H₂O. A coloring agent was added that reacts with sodium to form a blue compound that strongly absorbs light of a specific wavelength. Each solution was diluted to 100 mL. A control solution was also prepared with no NaCl added. 

The students used a colorimeter (which is a used to measure how much light of a selected wavelength is absorbed by a sample) in order determine the absorbance of each solution. T absorbances were then corrected by subtracting the absorbance of the control solution from reading. See Table 1.

Experiment 2

100 g drained samples of various canned vegetables were ground in a blender with 50 ml of H₂O. The resulting mixture was filtered, and then diluted to 100 mL. The students added the coloring agent to each solution. The students measured the absorbance of each solution using the colorimeter, with the results shown in Table 2.

Multiple Choice

Based on the results of Experiment 1, if the concentration of Na in the solution is doubled, then the corrected absorbance of the solution will approximately...

• Triple

• Double

• Halve

• Stay the same

The correct answer is B.

In Table 1, each time the concentration of Na doubles (for example, from 1.0 to 2.0) then the corrected absorbance also doubles (for example, from 0.1 to 0.2).

Multiple Choice

Based on the results of Experiment 1, if the concentration of Na in the solution is halved, then the corrected absorbance of the solution will approximately...

• Triple

• Double

• Halve

• Stay the same

The correct answer is C.

When the concentration of Na is halved in Table 1 (for example, from 4.0 to 2.0) then the corrected absorbance also decreases by half (in this example, from 0.4 to 0.2).

Multiple Choice

If a sample of peas were also included in Experiment 2, and the students measured its corrected absorbance at .321, then which of the following correctly lists corn, carrots and peas in increasing order of Na concentration?

• Peas, carrots, corn

• Corn, peas, carrots

• Carrots, peas, corn

• Corn, carrots, peas

The correct answer is C.

To answer this, first we have to spot the pattern that the concentration of Na for each vegetable is 10 times the corrected absorbance. Therefore we can predict that the Na concentration of peas is .321 x 10 = 3.21 ppm. Now we order the three vegetables in terms of increasing concentration. Carrots = 0.024, Peas = 3.21, and Corn = 4.39.

Multiple Choice

If a sample of peas were also included in Experiment 2, and the students measured its corrected absorbance at .321, then which of the following correctly lists mixed vegetables, green beans, and peas decreasing order of Na concentration?

• Peas, mixed vegetables, green beans

• Green beans, peas, mixed vegetables

• Peas, green beans, mixed vegetables

• Green beans, mixed vegetables, peas

The correct answer is B.

To answer this, first we have to spot the pattern that the concentration of Na for each vegetable is 10 times the corrected absorbance. Therefore we can predict that the Na concentration of peas is .321 x 10 = 3.21 ppm. Now we order the three vegetables in terms of decreasing concentration. Green beans = 5.52, Peas 3.21, and Mixed Vegetables = 1.23.

Multiple Choice

Using Table 1, what is the best prediction of the corrected absorbance of an Na solution with a concentration of 16 ppm?

• 0.4

• 1.2

• 1.7

• 1.6

The correct answer is D.

The pattern in Table 1 is that the corrected absorbance is the concentration divided by 10. 16/10 = 1.6.