I Don’t Take Science In School: Can I Still Score Highly In The ACT?



The short answer to this commonly-asked question is YES.

The ‘Science’ section of the ACT actually tests students’ data interpretation skills rather than their knowledge of scientific concepts. It’s true that a basic knowledge of foundational chemistry, physics, and biology is assumed, but any student who has taken science up to a Grade 10 level should have covered the topics in school. At essai, we go back over all of the essential science knowledge in just a few hours of class.

The key to succeeding in the Science section lies in developing an understanding of how to quickly interpret data, learning how to read tables and graphs, and becoming confident with  scientific methodology and experimental design.

Let’s look at an extract from the official ACT practice science section to see how one might tackle the questions WITHOUT using specific scientific factual knowledge:

Paper chromatography can be used to identify metal ions in wastewater. A drop of sample solution is placed on filter paper. The bottom of the paper is set in a solvent that travels up the paper (see Figure 1).

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Figure 1

The solvent carries the ions up the paper. Some ions move faster, and therefore farther than others, resulting in a separation as they move up the paper. The paper is dried, then stained, causing the ions to appear as colored spots. Rf values are calculated for each spot:

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Table 1 shows Rf values for 5 ions. Table 2 shows Rf values from 3 samples of wastewater. The same solvent was used for all ions and samples.

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Table 1 adapted from Thomas McCullough, CSC, and Marissa Curlee, “Qualitative Analysis of Cations Using Paper Chromatography.” ©1993 by the American Chemical Society.

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Note: Samples contain only the metal ions listed in Table 1.

Question 1: The information in Tables 1 and 2 supports the conclusion that Sample 3 contains:

  1. Cu2+ and Cd2+ only.

  2. Co2+ and Hg2+ only.

  3. Ni2+, Co2+, and Cd2+ only.

  4. Ni2+, Cd2+, and Hg2+ only

Answer Explanation: When the drop of wastewater Sample 3 is put on the filter paper and the filter paper is placed in the solvent solution, the ions from the sample travel up the filter paper with Rf values of 0.08, 0.78, and 0.95 (we can see this from the third row of Table 2).
If we cross-reference this information with the Rf of known ions in Table 1 then we can see that the sample must contain Nickel, Cadmium, and Mercury ions. Therefore the correct answer is D.

Question 2: Based on the information in Table 1, which of the following lists the metal ions in order from the fastest to slowest speed with which they moved up the paper?

  1. Hg2+, Cd2+, Cu2+, Co2+, Ni2

  2. Cd2+, Cu2+, Co2+, Hg2+, Ni2+

  3. Ni2+, Hg2+, Co2+, Cu2+, Cd2+

  4. Ni2+, Co2+, Cu2+, Cd2+, Hg2+

Answer Explanation: We know that the metal ion which travels the farthest distance in the set period of time in which the filter paper is placed in the solvent solution is the one which must also be travelling the fastest (remember the Math formula Speed= Distance/Time). To answer this question we look at Table 2, which happens to be ordered in increasing speed of ion travel. We just reverse the order of the table to find the correct answer (which is A).

Question 3:  Based on the information in Table 1, to best identify a metal ion using paper chromatography, one should know the:

  1. spot color for the ion only.

  2. distance the solvent traveled only.

  3. Rf value and spot color for the ion only.

  4. distance the solvent traveled and spot color of the ion only.

Answer Explanation: We start by looking at the data in Table 1 and eliminating options. The answer cannot be A, because some of the ions share the same spot color, therefore we cannot use this feature to differentiate between ions. The answer cannot be B, because the solvent would travel the same distance in all trials. It cannot be D, because that is a combination of the wrong answers A and B, and even having both sets of information would still not enable us to differentiate between ions. Therefore the correct answer must be C. Knowing the Rf value is the crucial piece of information, as it differs for each ion.

Passage and questions taken from: https://www.act.org/content/act/en/products-and-services/the-act/test-preparation/science-practice-test-questions.html?page=0&chapter=4#