ACT Science : Chemistry
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Example Questions
Example Question #121 : Chemistry
Current high levels of fossil fuel use, including coal-burning power plants and gasoline-powered automobiles, have helped contribute to the high concentrations of sulfur trioxide, SO3, found in the atmosphere. When sulfur trioxide and water interact, they can undergo the following chemical reaction to produce sulfuric acid, which is the main contributor to acid rain worldwide:
Acid rain showers are particularly common near coal-burning power plants and large cities. These showers are responsible for significant economic damage to sidewalks, roads, and buildings. Scientists interested in studying the effects of acid rain often use basic substances like calcium carbonate, the main component of limestone buildings, and expose them to varying volumes of acid rain to determine what volume of acid rain is necessary to begin to erode a building. A sample graph of one scientist’s experiment is replicated below:
Measuring acid and base levels is commonly done with a scale called pH, which uses the concentration of hydrogen ions to determine the acidity. Hydrogen ions are in a balance with hydroxide ions to give a scale with a range from 0 to 14. Values equal to or between 0 and 6.9 represent the acidic range where hydrogen ions predominate and values equal to or ranging from 7.1 and 14 represent the basic range where hydroxide ions predominate. Thus, the more hydrogen ions present, the more acidic the solution.
Scientists can tell when a titration (pH) experiment passes a certain pH using compounds called indicators. Indicators are usually colorless at pH levels below that of their specified color change. A table of indicators used by the above scientists and the pH at which they change colors is presented below.
Solutions A, B, and C each contain a different number of hydroxide ions. Solution A has a pH of 9.2, solution B has a pH of 10.3, and solution C has a pH of 7.3. Place the solutions in order of increasing number of hydroxide ions.
B < A < C
C < A < B
A < B < C
C < B < A
C < A < B
This question provides us with the pH of a few solutions and asks us to determine the relative number of hydroxide ions present. Thus, we need to convert the pH into a general idea of the number of hydrogen ions and then understand the relationship between hydrogen and hydroxide. From the passage, we know that a low pH means an abundance of hydrogen ions. Additionally, we know that when the hydrogen ion number is high, the hydroxide ion number is low (the paragraph below the provided graph). Thus, we can use these two pieces of information to correctly order the solutions.
Example Question #802 : Act Science
Current high levels of fossil fuel use, including coal-burning power plants and gasoline-powered automobiles, have helped contribute to the high concentrations of sulfur trioxide, SO3, found in the atmosphere. When sulfur trioxide and water interact, they can undergo the following chemical reaction to produce sulfuric acid, which is the main contributor to acid rain worldwide:
Acid rain showers are particularly common near coal-burning power plants and large cities. These showers are responsible for significant economic damage to sidewalks, roads, and buildings. Scientists interested in studying the effects of acid rain often use basic substances like calcium carbonate, the main component of limestone buildings, and expose them to varying volumes of acid rain to determine what volume of acid rain is necessary to begin to erode a building. A sample graph of one scientist’s experiment is replicated below:
Measuring acid and base levels is commonly done with a scale called pH, which uses the concentration of hydrogen ions to determine the acidity. Hydrogen ions are in a balance with hydroxide ions to give a scale with a range from 0 to 14. Values equal to or between 0 and 6.9 represent the acidic range where hydrogen ions predominate and values equal to or ranging from 7.1 and 14 represent the basic range where hydroxide ions predominate. Thus, the more hydrogen ions present, the more acidic the solution.
Scientists can tell when a titration (pH) experiment passes a certain pH using compounds called indicators. Indicators are usually colorless at pH levels below that of their specified color change. A table of indicators used by the above scientists and the pH at which they change colors is presented below.
A scientist wants to titrate a solution of sodium hydroxide at a pH of 14 with an acidic solution of phosporic acid at a pH of 10. She is attempting to create a solution that can mimic a basic environment. Which indicator would she likely use?
Methyl Red
Cannot Be Determined
Isobutyl Terpine
Propyl Cyonate
Methyl Red
This questions asks us to use the provided table to determine which indicator would be useful for use in the proposed experiment. In order to determine which indicator our scientist should use, we need to know the meaning of basic. The information contained in the passage, namely the paragraph below the curved graph, allows us to determine that a basic solution is above a pH of 7. Thus, our scientist would want to titrate to a pH around 9.2 using methyl red.
Example Question #122 : Chemistry
Current high levels of fossil fuel use, including coal-burning power plants and gasoline-powered automobiles, have helped contribute to the high concentrations of sulfur trioxide, SO3, found in the atmosphere. When sulfur trioxide and water interact, they can undergo the following chemical reaction to produce sulfuric acid, which is the main contributor to acid rain worldwide:
Acid rain showers are particularly common near coal-burning power plants and large cities. These showers are responsible for significant economic damage to sidewalks, roads, and buildings. Scientists interested in studying the effects of acid rain often use basic substances like calcium carbonate, the main component of limestone buildings, and expose them to varying volumes of acid rain to determine what volume of acid rain is necessary to begin to erode a building. A sample graph of one scientist’s experiment is replicated below:
Measuring acid and base levels is commonly done with a scale called pH, which uses the concentration of hydrogen ions to determine the acidity. Hydrogen ions are in a balance with hydroxide ions to give a scale with a range from 0 to 14. Values equal to or between 0 and 6.9 represent the acidic range where hydrogen ions predominate and values equal to or ranging from 7.1 and 14 represent the basic range where hydroxide ions predominate. Thus, the more hydrogen ions present, the more acidic the solution.
Scientists can tell when a titration (pH) experiment passes a certain pH using compounds called indicators. Indicators are usually colorless at pH levels below that of their specified color change. A table of indicators used by the above scientists and the pH at which they change colors is presented below.
If a scientist wanted to determine roughly when 22 mL of phosphoric acid had been added to a solution of sodium hydroxide, he would likely choose which indicator?
Methyl Red
Isobutyl Terpine
Cannot Be Determined
Propyl Cyonate
Isobutyl Terpine
According to the graph provided, adding 22 mL of an acid to a sodium hydroxide solution gives a pH around 7. Thus, our scientist would want to use an indicator that works around that pH, namely isobutyl terpine.
Example Question #123 : Chemistry
Current high levels of fossil fuel use, including coal-burning power plants and gasoline-powered automobiles, have helped contribute to the high concentrations of sulfur trioxide, SO3, found in the atmosphere. When sulfur trioxide and water interact, they can undergo the following chemical reaction to produce sulfuric acid, which is the main contributor to acid rain worldwide:
Acid rain showers are particularly common near coal-burning power plants and large cities. These showers are responsible for significant economic damage to sidewalks, roads, and buildings. Scientists interested in studying the effects of acid rain often use basic substances like calcium carbonate, the main component of limestone buildings, and expose them to varying volumes of acid rain to determine what volume of acid rain is necessary to begin to erode a building. A sample graph of one scientist’s experiment is replicated below:
Measuring acid and base levels is commonly done with a scale called pH, which uses the concentration of hydrogen ions to determine the acidity. Hydrogen ions are in a balance with hydroxide ions to give a scale with a range from 0 to 14. Values equal to or between 0 and 6.9 represent the acidic range where hydrogen ions predominate and values equal to or ranging from 7.1 and 14 represent the basic range where hydroxide ions predominate. Thus, the more hydrogen ions present, the more acidic the solution.
Scientists can tell when a titration (pH) experiment passes a certain pH using compounds called indicators. Indicators are usually colorless at pH levels below that of their specified color change. A table of indicators used by the above scientists and the pH at which they change colors is presented below.
If a scientist wanted to determine roughly when 26 mL of phosphoric acid had been added to a solution of sodium hydroxide, he would likely choose which indicator?
Cannot Be Determined
Propyl Cyonate
Methyl Red
Isobutyl Terpine
Propyl Cyonate
The question asks us to predict the indicator chosed by our scientist in the experiment. Using the graph provided, we can see that the pH is somewhere around 4 when the required volume of acid is added. Thus, we would want to choose an indicator that works around this pH. Using the options provided in the chart, we would likely choose propyl cyonate.
Example Question #806 : Act Science
A brilliant but underpaid high school chemistry teacher, together with his former student, manufactures a chemical compound, which they sell for a large mark-up. Their set of reactions are given below:
(1) A + B + C + acid --> D
(2) D --> intermediate
(3) Intermediate --> E
(4) E + acid --> X
His student notes the following observations:
Observation 1) If a greater amount of B and C are used in the reaction, this yields no increased amount of product D.
Observation 2) At any given point, D, the intermediate, and E may co-exist in equal proportions. However, at higher temperatures, higher proportions of product E are noted.
Observation 3) The addition of a strong base can reverse reaction 4.
Which of the following is true of the effects of temperature on reactions 2 and 3?
Since at higher temperatures more of product E exists, reactions 2 and 3 can be considered exothermic (heat-producing).
Regardless of the temperature, the intermediate is the most stable product.
Since at higher temperatures more of product E exists, reactions 2 and 3 can be considered endothermic (heat-needing).
No relationship between heat, reaction 2, and reaction 3 can be concluded.
Since at higher temperatures more of product E exists, reactions 2 and 3 can be considered endothermic (heat-needing).
Observation 2 illustrates that at higher temperatures more of product E will exist. This suggests that heat may help drive the reaction forward, indicating that the reaction of D to intermediate to E is endothermic (needing heat). Not enough information is supplied to determine which product is the most stable; however, the fact that more of E exists at higher temperatures may also indicate that it is a more stable compound. Generally, a compound will take the most stable form at higher temperatures.
Example Question #121 : Chemistry
A brilliant but underpaid high school chemistry teacher, together with his former student, manufactures a chemical compound, which they sell for a large mark-up. Their set of reactions are given below:
(1) A + B + C + acid --> D
(2) D --> intermediate
(3) Intermediate --> E
(4) E + acid --> X
His student notes the following observations:
Observation 1) If a greater amount of B and C are used in the reaction, this yields no increased amount of product D.
Observation 2) At any given point, D, the intermediate, and E may co-exist in equal proportions. However, at higher temperatures, higher proportions of product E are noted.
Observation 3) The addition of a strong base can reverse reaction 4.
Adding a strong base will have which of the following effects?
(I) Convert X into E.
(II) Limit the amount of D formed in reaction 1.
(III) Convert E into D.
(IV) No effects.
II and III
I and II
III
IV
I and III
I and II
Observation III indicates that adding a base can convert X back into E, thus reversing the reaction. If adding a base nullifies the actions of an acid in reaction 4, it can also be inferred that it can have the same effect in reaction I. Therefore, options I and II are correct. Option IV can automatically be ruled out because there is an effect of adding a strong base. There is no information suggesting that adding a base will convert E back into D, as option III suggests.
Example Question #125 : Chemistry
A brilliant but underpaid high school chemistry teacher, together with his former student, manufactures a chemical compound, which they sell for a large mark-up. Their set of reactions are given below:
(1) A + B + C + acid --> D
(2) D --> intermediate
(3) Intermediate --> E
(4) E + acid --> X
His student notes the following observations:
Observation 1) If a greater amount of B and C are used in the reaction, this yields no increased amount of product D.
Observation 2) At any given point, D, the intermediate, and E may co-exist in equal proportions. However, at higher temperatures, higher proportions of product E are noted.
Observation 3) The addition of a strong base can reverse reaction 4.
Reagents B and C are relatively inexpensive compared to A. What can be expected if twice the number of moles of B and C are used in reaction 1 with the number of moles of A held constant?
Eight times the amount of D produced
Half the amount of D produced
Twice the amount of D produced
No change in in the amount of D produced
Four times the amount of D produced
No change in in the amount of D produced
Observation 1 states that adding additional B or C has no effect in increased yield of D. From this statment, we can infer that reagent A is the "limiting reagent." In other words, the amount of D formed is entirely dependent on the amount of A available; therefore, doubling the amount of number of moles of B and C will not increase or decrease the amount of D formed.
Example Question #811 : Act Science
A brilliant but underpaid high school chemistry teacher, together with his former student, manufactures a chemical compound, which they sell for a large mark-up. Their set of reactions are given below:
(1) A + B + C + acid --> D
(2) D --> intermediate
(3) Intermediate --> E
(4) E + acid --> X
His student notes the following observations:
Observation 1) If a greater amount of B and C are used in the reaction, this yields no increased amount of product D.
Observation 2) At any given point, D, the intermediate, and E may co-exist in equal proportions. However, at higher temperatures, higher proportions of product E are noted.
Observation 3) The addition of a strong base can reverse reaction 4.
Without the addition of acid, reactions 1 and 4 proceed at a much slower rate. What is the role of acid in these reactions?
An additive; the acid shifts the equilbrium constants of these reactions to produce more product.
No role in these reactions.
A reagent (or substrate); the acid is needed as reagent for completion of these reactions.
A catalyst; the acid lowers the activation energy of these reactions and helps them proceed more quickly.
A catalyst; the acid lowers the activation energy of these reactions and helps them proceed more quickly.
The acid can be thought of as a catalyst. The question states that these reactions can proceed without acid, but at a much slower rate; therefore, acid is not needed for these reactions and is not a reagent or substrate; however, its presence will speed the rate of the reactions. Catalysts do not alter the equilibirum constant of a reaction. In other words, they will change the speed or rate of which product is produced, but once the reaction has carried out to completion and each agent is in equilibirum, there will not be relatively more product present because of the acid.
Example Question #812 : Act Science
A brilliant but underpaid high school chemistry teacher, together with his former student, manufactures a chemical compound, which they sell for a large mark-up. Their set of reactions are given below:
(1) A + B + C + acid --> D
(2) D --> intermediate
(3) Intermediate --> E
(4) E + acid --> X
His student notes the following observations:
Observation 1) If a greater amount of B and C are used in the reaction, this yields no increased amount of product D.
Observation 2) At any given point, D, the intermediate, and E may co-exist in equal proportions. However, at higher temperatures, higher proportions of product E are noted.
Observation 3) The addition of a strong base can reverse reaction 4.
If reaction 4 is conducted in isolation, removing some of the product, X, will have which of the following effects?
Help reverse the reaction and convert more of the remaining X back into E
No effect
Similar effect to adding more of E
Decreasing the amount of X subsequently produced
Similar effect to adding more of E
This question asks you to understand the concept of Le Chatelier's Principle, which states that either adding more reagents or removing more product will shift the reaction to the right, and produce more product. By removing X, you will achieve the same affect of adding more of E. Conceptually, this principle can be thought of as a reaction trying to go back to its original state. If product is removed, the reaction will try to replace that product, and thus form more of it.
Example Question #811 : Act Science
A student wished to study the acidity and basicity of various household ingredients and chemicals using her own, homemade pH indicator. A pH indicator is a substance that changes colors to indicate the acidity or basicity of a chemical solution. Acids can be defined as substances that donate hydrogen ions, or H+, while bases are substances that accept H+ ions. The strength of these acids and bases can be measured using the pH scale as shown in Figure 1.
Experiment 1:
The student placed a leaf of red cabbage in a blender with one liter of water and blended until the cabbage had been liquefied. She then strained the purple mixture and bottled it. The student then added one drop of her homemade cabbage pH indicator to a variety of household chemicals listed in Table 1. She recorded the known pH of these chemicals as well as the color the indicator turned when added to these chemicals.
Experiment 2:
The student wanted to see how baking soda would react in the presence of other household chemicals. She combined baking soda in water separately with each of the other chemicals used in Experiment 1. Some combinations would create bubbling while some other combinations wouldn't. She recorded the results in Table 2 below.
What can be inferred from Experiment 2?
Baking soda only produces bubbles in the presence of a chemical with a neutral pH.
Baking soda only produces bubbles in the presence of an acid.
Baking soda only produces bubbles in the presence of a base.
None of the other answers is correct.
Baking soda only produces bubbles in the presence of an acid.
Baking soda reacts, or produces bubbles, with lemon juice, vinegar, toilet bowl cleaner, and soda pop only. By cross-referencing Table 1, we see that these substances have a pH of less than 7, which is the definition of an acid as Figure 1 shows. Thus, we know that baking soda only reacts with acids.
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