ACT Science : Chemistry
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Example Questions
Example Question #761 : Act Science
The rate of a reaction is defined as the rate at which the products of a reaction are produced. A researcher wants to investigate the rate of reaction of the combustion of theoretical compound 
The results of the experiment are shown in the table below. The brackets ([]) indicate concentration measured in mol/L.
Which of the following is the best explanation for the repetition of trial 1 during the experiment?
Repeating trial 1 revealed that the results of trials 2 and 3 were due to chance.
Repeating trial 1 ensured the original results of trial 1 were due to chance.
Repeating trial 1 caused the reactions measured in trials 2 and 3.
Repeating trial 1 did not serve any purpose.
Repeating trial 1 acted as a control.
Repeating trial 1 acted as a control.
This question is a bit tricky because it can be easy to get distracted with the other answers. If you go back into the passage, you see that the researcher expressed concern that the lab's conditions could change and therefore could affect measurements. Therefore, repeating trial 1 during the experiment was simply a control to account for possible changes in the lab that could affect the results. As it states in the passage, the researcher's concerns were unfounded, and repeating trial 1 was indeed unnecessary. However, that does not mean that it did not serve the purpose of proving to the researcher that the conditions of the lab stayed steady throughout the experiment—which is well worth the additional effort.
Example Question #81 : Chemistry
The above chemical equation describes the dissociation of carbonic acid 
When carbon dioxide 
To study this effect, the student obtains a mixture of carbonic acid, bicarbonate, and hydrogen ion. Next, the student conducts trials in which she adds a certain amount of one of the chemicals one at a time and then measures how the concentrations of each chemical change after each addition.
What can we infer would happen if the student were to add hydrochloric acid (a source of hydrogen ions) into a flask of a predetermined amount of carbonic acid, bicarbonate, and hydrogen ion?
Both the concentration of bicarbonate and carbonic acid would decrease.
The concentrations would not change.
The concentration of bicarbonate would decrease and the concentration of carbonic acid would increase.
The concentration of bicarbonate would increase, and the concentration of carbonic acid would decrease.
Both the concentration of bicarbonate and carbonic acid would increase.
The concentration of bicarbonate would decrease and the concentration of carbonic acid would increase.
For this question, we must have a firm understanding of the passage's description of equilibrium. In summary, the passage states that adding more of a chemical on one half of the chemical equation will shift equilibrium to the other direction. Therefore, if we add more hydrogen ion with hydrochloric acid, we know that equilibrium will shift left. This would mean that more carbonic acid would form, so it would increase while decreasing the amount of bicarbonate ion.
Example Question #761 : Act Science
Kevin wants to know if a particular kind of chemical fertilizer will help or hinder the growth of his tomato plants. He decides to conduct an experiment in which he grows three plants, one left untreated, one treated with the chemical fertilizer RapidGro and one treated with an organic compost. He records his findings in the charts below, measuring plant height and number of tomatoes over a period of time.
Height of plant (inches):
|
Day |
No Fertilizer |
RapidGro |
Compost |
|
1 |
3 |
3 |
3 |
|
2 |
5 |
6 |
4 |
|
3 |
7 |
9 |
6 |
|
4 |
9 |
12 |
8 |
|
7 |
15 |
21 |
14 |
|
10 |
16 |
21 |
19 |
|
14 |
18 |
18 |
21 |
Number of tomatoes:
|
Day |
No fertilizer |
RapidGro |
Compost |
|
1 |
0 |
0 |
0 |
|
2 |
1 |
2 |
1 |
|
3 |
1 |
3 |
2 |
|
4 |
2 |
4 |
3 |
|
7 |
4 |
7 |
5 |
|
10 |
6 |
7 |
6 |
|
14 |
6 |
4 |
7 |
On the fourteenth day Kevin picks the biggest tomato from each plant and record its dimensions, as well as other information, which is found below.
Tomato 1 (no fertilizer): 
Tomato 2 (RapidGro): 
Tomato 3 (compost): 
Which plant is the control?
There is no control
The plant with chemical fertilizer
The plant with compost
The plant without fertilizer or compost
The plant without fertilizer or compost
In an experiment, the control is what does not change or remains untreated by the variables being tested, in this case the fertilizer or compost.
Example Question #11 : How To Find Experimental Design In Chemistry
The Environmental Protection Agency compiled the following information about heavy metals in drinking water. Heavy metals are toxic, and thus must be monitored very closely. All amounts are given in parts per billion (ppb), a common measurement of concentration for trace contaminants. Figure 1 shows total heavy metal contamination in each city as a makeup of various percentages of specific contaminants. Figure 2 shows specific amounts of contaminants (with the same color coding) in ppb as well as total contamination level in ppb.
Figure 1
Figure 2
Which city has the most total cadmium in parts per billion?
Boston
Miami
Fargo
Chicago
Boston
Figure 2, which shows total amount of contamination by contaminant, indicates cadmium contamination in yellow. Note that the yellow bar for Boston is clearly the largest, indicating 2.5ppb of cadmium.
Example Question #761 : Act Science
The Environmental Protection Agency compiled the following information about heavy metals in drinking water. Heavy metals are toxic, and thus must be monitored very closely. All amounts are given in parts per billion (ppb), a common measurement of concentration for trace contaminants. Figure 1 shows total heavy metal contamination in each city as a makeup of various percentages of specific contaminants. Figure 2 shows specific amounts of contaminants (with the same color coding) in ppb as well as total contamination level in ppb.
Figure 1
Figure 2
Which contaminant is most abundant in Fargo?
Cadmium
Beryllium
Mercury
Lead
Mercury
Either chart (the pie chart labeled Fargo, or the bar for Fargo on the bar graph) shows that the green contaminant, mercury, is the most abundant. Antimony, shown in red, may be a close second, however, this answer choice is not available.
Example Question #21 : How To Find Experimental Design In Chemistry
The Environmental Protection Agency compiled the following information about heavy metals in drinking water. Heavy metals are toxic, and thus must be monitored very closely. All amounts are given in parts per billion (ppb), a common measurement of concentration for trace contaminants. Figure 1 shows total heavy metal contamination in each city as a makeup of various percentages of specific contaminants. Figure 2 shows specific amounts of contaminants (with the same color coding) in ppb as well as total contamination level in ppb.
Figure 1
Figure 2
A scientist wants to publish a paper about water treatment standards in the United States. Which figure is a better figure to include in her report?
Figure 2, because it shows both relative amounts of each contaminant in various cities, and also because it shows numerical amounts of each contaminant in ppb.
Figure 1, because it shows the numerical amounts of each contaminant in ppb, a useful metric.
Figure 1, because it shows percent contamination most clearly, and this is the most important piece of data for contamination studies.
Figure 2, because it shows which cities have the most total contamination.
Figure 2, because it shows both relative amounts of each contaminant in various cities, and also because it shows numerical amounts of each contaminant in ppb.
Figure 2 shows the relative amounts of each contaminant. For example, you can see that Fargo clearly has more mercury contamination, shown in green, than Boston, by comparing the relative heights of the green part of the two bars. The figure also shows numerical amounts of contaminant in ppb on the y-axis. We can see the amount of each contaminant in each city in ppb or the total amount of contamination in ppb.
Figure 1 shows relative contaminant amounts as a percentage of the total of each city's total contamination. It gives no data whatsoever about numerical parts per billion contaminant concentrations. This second type of information is probably more important for scientists to truly understand the degree of contamination in each of these cities.
While Figure 2 does show which cities have the most total contamination, it is not the sole reason that Figure 2 is the more useful figure. The other statement about Figure 2 is a more complete answer.
It is true that Figure 1 shows percent contamination more clearly than Figure 2. However, as Figure 2 imparts more information in total, including percentage information, it is more useful. Additionally, percent contamination of a total wherein the totals for each city differ does not give a lot of information that can be compared city to city.
Example Question #81 : Chemistry
Naturally occurring water in lakes and reservoirs used as sources for drinking water feature a variety of dissolved minerals such as magnesium, sodium, and calcium. Water treatment plants must closely monitor the levels of these minerals to ensure they do not exceed unsafe levels. An experiment carried out by a scientist at a water treatment plant are described below.
Experiment 1:
A common way to determine the concentration of a particular chemical is by titration. In this titration, 10mL of the treated water sample was placed in a flask as shown below in Figure 1. A buret, (a special funnel with volume markings on the side and a knob on the bottom to control how much of the substance in the buret is dispensed) was placed above the flask as shown in Figure 1. It was filled with 50mL of a 20ppm (parts per million) solution of EDTA, a chemical that can react with magnesium to chemically remove it from the water. An indicator (a substance that changes color to indicate a chemical change) was also placed into the flask; this indicator appears purple in water solutions containing magnesium, and blue in water solutions without magnesium. The buret was used to dispense EDTA solution until enough EDTA had been added to the purple magnesium-containing water solutions to remove all the magnesium and turn the solution blue. The volume, in milliliters, of EDTA solution added to each of five water samples is recorded in Table 1.
Figure 1
The formula for parts per million (ppm) of magnesium 
We see from Table 1 that the average volume of EDTA solution added is approximately 30mL. Use this value and the given equation to solve for the parts per million of magnesium.
Example Question #24 : How To Find Experimental Design In Chemistry
Naturally occurring water in lakes and reservoirs used as sources for drinking water feature a variety of dissolved minerals such as magnesium, sodium, and calcium. Water treatment plants must closely monitor the levels of these minerals to ensure they do not exceed unsafe levels. An experiment carried out by a scientist at a water treatment plant are described below.
Experiment 1:
A common way to determine the concentration of a particular chemical is by titration. In this titration, 10mL of the treated water sample was placed in a flask as shown below in Figure 1. A buret, (a special funnel with volume markings on the side and a knob on the bottom to control how much of the substance in the buret is dispensed) was placed above the flask as shown in Figure 1. It was filled with 50mL of a 20ppm (parts per million) solution of EDTA, a chemical that can react with magnesium to chemically remove it from the water. An indicator (a substance that changes color to indicate a chemical change) was also placed into the flask; this indicator appears purple in water solutions containing magnesium, and blue in water solutions without magnesium. The buret was used to dispense EDTA solution until enough EDTA had been added to the purple magnesium-containing water solutions to remove all the magnesium and turn the solution blue. The volume, in milliliters, of EDTA solution added to each of five water samples is recorded in Table 1.
Figure 1
Water that does not allow soap to lather well is called "hard water". Hardness is caused by the presence of magnesium. Given the following water classification system, how would the water tested by the scientist be classified?
Soft
Slightly hard
Very hard
Moderately hard
Moderately hard
The water sampled contains approximately 60ppm magnesium. Given the classification chart, we see that 60ppm falls within the ppm range listed for moderately hard.
Example Question #25 : How To Find Experimental Design In Chemistry
Naturally occurring water in lakes and reservoirs used as sources for drinking water feature a variety of dissolved minerals such as magnesium, sodium, and calcium. Water treatment plants must closely monitor the levels of these minerals to ensure they do not exceed unsafe levels. An experiment carried out by a scientist at a water treatment plant are described below.
Experiment 1:
A common way to determine the concentration of a particular chemical is by titration. In this titration, 10mL of the treated water sample was placed in a flask as shown below in Figure 1. A buret, (a special funnel with volume markings on the side and a knob on the bottom to control how much of the substance in the buret is dispensed) was placed above the flask as shown in Figure 1. It was filled with 50mL of a 20ppm (parts per million) solution of EDTA, a chemical that can react with magnesium to chemically remove it from the water. An indicator (a substance that changes color to indicate a chemical change) was also placed into the flask; this indicator appears purple in water solutions containing magnesium, and blue in water solutions without magnesium. The buret was used to dispense EDTA solution until enough EDTA had been added to the purple magnesium-containing water solutions to remove all the magnesium and turn the solution blue. The volume, in milliliters, of EDTA solution added to each of five water samples is recorded in Table 1.
Figure 1
A new EDTA titration solution is prepared with 40ppm EDTA. Approximately how much EDTA titration solution should the scientist expect to use to titrate a 10mL sample of the same water?
The equation in question 1, shown below, states that ppm of magnesium is given by multiply the volume of titration solution used by the ppm of EDTA in the titration solution, all divided by the volume of water in the sample.
By filling in the known 60ppm magnesium in the water sample as was determined in question 1, and replacing the original 20ppm concentration of EDTA in the solution with 40ppm, we see that:
Alternatively, we see that because the concentration has doubled, half as much will be used to remove the magnesium. As an average of 30mL was used in the original experiment, we can see that 15mL will now be used.
Example Question #81 : Chemistry
Naturally occurring water in lakes and reservoirs used as sources for drinking water feature a variety of dissolved minerals such as magnesium, sodium, and calcium. Water treatment plants must closely monitor the levels of these minerals to ensure they do not exceed unsafe levels. An experiment carried out by a scientist at a water treatment plant are described below.
Experiment 1:
A common way to determine the concentration of a particular chemical is by titration. In this titration, 10mL of the treated water sample was placed in a flask as shown below in Figure 1. A buret, (a special funnel with volume markings on the side and a knob on the bottom to control how much of the substance in the buret is dispensed) was placed above the flask as shown in Figure 1. It was filled with 50mL of a 20ppm (parts per million) solution of EDTA, a chemical that can react with magnesium to chemically remove it from the water. An indicator (a substance that changes color to indicate a chemical change) was also placed into the flask; this indicator appears purple in water solutions containing magnesium, and blue in water solutions without magnesium. The buret was used to dispense EDTA solution until enough EDTA had been added to the purple magnesium-containing water solutions to remove all the magnesium and turn the solution blue. The volume, in milliliters, of EDTA solution added to each of five water samples is recorded in Table 1.
Figure 1
A sample of tap water from somewhere else was treated with the indicator and was shown to produce a blue solution without the addition of any EDTA. What should the researcher conclude?
There is a large amount of magnesium
There is no appreciable amount of magnesium present in the tap water
EDTA is naturally present in the water
Some else has already treated the sample with EDTA
There is no appreciable amount of magnesium present in the tap water
A blue solution in response to the addition of indicator is said, in the introduction, to be indicative of no chemically available magnesium. It is most likely that there is naturally very low levels of magnesium in the water than that someone had already added EDTA or that it occurs naturally, given that it is a common laboratory chemical.
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