ACT Science : How to find experimental design in chemistry
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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.
Example Question #771 : Act Science
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
If a sample of tap water from elsewhere had a magnesium concentration of 100ppm, how much of the original 20ppm EDTA titrant can be expected to be used?
W can calculate the volume of titrant using the following equation setup:
Example Question #772 : Act Science
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
Why does the researcher use the buret?
This is the best way to control exactly the amount of EDTA solution added to be able to calculate an accurate concentration of magnesium
This is a good way to provide a control for the experiment
The EDTA solution must be kept separate from the water solution
This way the researcher doesn't have to add the EDTA titrant manually
This is the best way to control exactly the amount of EDTA solution added to be able to calculate an accurate concentration of magnesium
It states in the introduction that a buret is a good way to control the exact amount of EDTA titrant added, and as we saw in other questions, the amount of titrant added is how we calculate magnesium concentrations.
Example Question #29 : How To Find Experimental Design In Chemistry
Solutions are made by dissolving a solute into a solvent. Different types of solvents have varying levels of solubility, or ability to dissolve certain substances.
A student decided to conduct an experiment to compare the solubilities of different solvents at different temperatures using table salt (sodium chloride) as a solute. The student would keep an amount of solvent at the specified temperature and add solute until no more solute would dissolve. This is amount or solute is called the point of saturation. The amount added to each solvent at saturation was recorded. The results of the experiment are shown in the tables:
Table 1:
Table 2:
Supersaturation is a state of a solution in which there is more solute in the solvent than predicted theoretically possible. A supersaturated solution is created by increasing the solubility of a solution past the amount of solute already dissolved in the solvent. Based on this information, which of the following procedures would allow us to create a supersaturated solution out of water?
Start with the same quantity of water used in the experiment. Dissolve 43 g of salt in the solution at 35 degrees Celsius. Cool the solution to 20 degrees Celsius.
Start with the same quantity of water used in the experiment. Dissolve 43 g of salt in the solution at 20 degrees Celsius. Heat the solution to 35 degrees Celsius.
Start with the same quantity of water used in the experiment. Dissolve 43 g of salt in the solution at 20 degrees Celsius. Double the pressure on the solution.
Start with the same quantity of water used in the experiment. Dissolve 43 g of salt in the solution at 20 degrees Celsius. Heat the solution to 35 degrees Celsius.
Start with the same quantity of water used in the experiment. Heat to 35 degrees Celsius. Dissolve 52 grams of salt in the solution and then cool to 20 degrees Celsius.
Start with the same quantity of water used in the experiment. Heat to 35 degrees Celsius. Dissolve 52 grams of salt in the solution and then cool to 20 degrees Celsius.
The correct procedure is that which involves saturating the solution at a higher temperature and then cooling that solution to a temperature at which the amount dissolved in the solvent is more than the theoretical point of saturation. Therefore the answer is saturating the solution at 35 degrees Celsius and simply cooling the solution to 20 degrees Celsius.
Example Question #30 : How To Find Experimental Design In Chemistry
Benzophenones are commonly added to cosmetics as UV stabilizers. By adding these chemicals, the cosmetics become less susceptible to breakdown by ultraviolet (UV) radiation. Oxybenzone and dioxybenzone are examples of benzophenones used in cosmetics.
A sunscreen company has received complaints about the longevity of its products and wants to see if adding benzophenones can alleviate this issue. They design an experiment with the following groups.
1. Sunscreen containing 
2. Sunscreen containing 
3. Sunscreen containing 
4. Sunscreen containing 
Each group is exactly the same aside from the added benzophenones. The company plans to expose each sample to high levels of UV radiation for 10 days and then test the effectiveness of each sample.
What could be changed to strengthen the experiment?
Adding a control group with no benzophenones added.
Nothing could be changed to strengthen the experiment.
Adding groups with more concentrations of benzophenones.
Removing the 
Exposing the samples to UV radiation for a longer period.
Adding a control group with no benzophenones added.
In order to test whether a change to their sunscreen will improve its resistance to UV radiation, the experiment must include the original product as a control. The impact of benzophenones requires a proper control group to be interpreted.
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