GRE Subject Test: Chemistry : Analytical Chemistry
Study concepts, example questions & explanations for GRE Subject Test: Chemistry
All GRE Subject Test: Chemistry Resources
Example Questions
Example Question #1 : Calculating Error
Robert conducted an experiment in which he investigated how much water a paper towel could absorb. Initially, Robert found that one paper towel can absorb 12.8g of water. Later he found that his scale was not calibrated, so he had to repeat the experiment. After repeating the experiment with a new scale, Robert found that one paper towel can actually absorb 32.9g of water. What is the approximate percent error between the findings of the first and second experiments?
The formula for percent error is:
In this case, the measured value is 12.8g and the accepted value is 32.9g.
Example Question #2 : Calculating Error
A reaction between one mole of sodium and one mole of chloride should yield 42 grams of sodium chloride. In your experiment, the actual yield is 32.73 grams. Calculate the percent error of your experiment.
To find percent error we need to use the following equation:
Plug in 42 for the theoretical yield and 32.73 for the actual yield and solve accordingly.
Example Question #3 : Calculating Error
In the following reaction, eight moles of sodium hydroxide is broken down into four moles of sodium oxide and four moles of water. What is the percent error if your experiment yields 195 grams of sodium oxide?
To find the percent error we need to use the following equation:
But in order to do this, we first have to convert moles of sodium oxide into grams:
This gives us a theoretical yield of 248g, which we plug in with our 195g actual yield.
Example Question #4 : Calculating Error
If a given sample of silver and flourine ideally combine to form 0.6mol of AgF, what is the percent error if the actual yield is 43 grams?
Our first step to complete this problem is to convert moles AgF into grams:
This gives us a theoretical yield of 76.2 grams. We can find the percent error by plugging in 76.2g for our theoretical yield and 43g for the actual yield in the following equation:
Example Question #1 : Understanding Accuracy And Precision
Michael buys several bags of balloons. On the package, it says that each bag has 100 balloons. He opens the bags and only one of them has 100 balloons inside; the other bags either have too many or too few.
How would you describe the bag of balloons with 100 balloons inside?
Precise, but not accurate
Neither accurate nor precise
Accurate, but not precise
Accurate, but the precision cannot be determined
Both accurate and precise
Accurate, but not precise
This bag is accurate because it provided the correct number of balloons, however, the process is not precise as the results were clearly not repeatable.
Accuracy deals with how close the measurement got to the accepted measurement. Precision deals with how consistent the measurement is. The bag with 100 balloons inside matched the claim made on the bag, meaning it was accurate. It was not precise because the other measurements show that the number of balloons is variable.
Example Question #2 : Analytical Chemistry
Michael's scale measures the mass of objects as consistently 
Accuracy and precision are synonyms
It is precise, but not accurate
It is neither accurate nor precise
It is accurate, but not precise
It is both accurate and precise
It is precise, but not accurate
Precision measures is how consistently a device records the same answer. In this case, Michael's scale is ALWAYS 
Accuracy is how well a device measures something against its accepted value. In this case, Michael's scale is not accurate because it is always off by 
Example Question #2 : Analytical Chemistry
An brand of fruit snacks claims that each bag of fruit snacks has a mass of 
How can Wally describe the accuracy and precision of the first bag he measured?
Precise, but not accurate
Accurate and precise
Accurate, but not precise
There are insufficient data points to draw a conclusion
Neither accurate nor precise
Accurate, but not precise
The claim for the mass of the first bag is accurate; the brand says there should be 
The claim on the first bag is not precise, as the results are not replicated universally throughout the experiment. The masses of the bags fluctuate, with the average of all three bags equal to 
Example Question #2 : Understanding Accuracy And Precision
A bowman is shooting arrows at a target. Which of the following demonstrates high accuracy but low precision?
The bowman consistently hits the bullseye
The bowman consistently hits around the target but never hits the bullseye
The bowman consistently hits to the right of the bullseye
The bowman consistently hits to the left of the target
The bowman consistently misses the target and hits a tree in the same spot
The bowman consistently hits around the target but never hits the bullseye
Accuracy is measured as the degree of closeness to the actual measurement. In our case, accurate shots will hit the bullseye. Precision is measured as the degree of closeness of one measurement to the next. In our case, precise shots will be clustered together.
To get high accuracy but low precision, measurements must center around the target value but be variable. The bowman's arrows will not be clustered (low precision), but will be accurately distributed around the bullseye. If all the shots were averaged, the bullseye would be at the center.
Example Question #2 : Understanding Accuracy And Precision
Which of these is an example of high precision?
A student tries to throw a pencil into the garbage can and makes it in
A student correctly calculates the mass of an object to be 54kg
An archer hits the same spot on the target three times in a row
An archer hits the bulls-eye
A student correctly calculates the acceleration due to gravity to be
An archer hits the same spot on the target three times in a row
Precision is a measure of reproducibility. If multiple trials produce the same result each time with minimal deviation, then the experiment has high precision. This is true even if the results are not true to the theoretical predictions; an experiment can have high precision with low accuracy.
In contrast, accuracy is the measure of difference between a calculated value and the true value of a measurement. High accuracy demands that the experimental result be equal to the theoretical result.
An archer hitting a bulls-eye is an example of high accuracy, while an archer hitting the same spot on the bulls-eye three times would be an example of high precision.
Example Question #5 : Analytical Chemistry
Which of these is an example of high accuracy?
An archer hits the bulls-eye
A student repeatedly calculates the mass of an object to be 49 grams, when the true mass is 52 grams
An archer hits the same spot on the target three times in a row
A student throws three pencils into the trash can, but misses and hits the window each time
A student calculates the acceleration due to gravity to be 
An archer hits the bulls-eye
Accuracy is the measure of difference between a calculated value and the true value of a measurement. High accuracy demands that the experimental result be equal to the theoretical result.
In contrast, precision is a measure of reproducibility. If multiple trials produce the same result each time with minimal deviation, then the experiment has high precision. This is true even if the results are not true to the theoretical predictions; an experiment can have high precision with low accuracy.
An archer hitting a bulls-eye is an example of high accuracy, while an archer hitting the same spot on the bulls-eye three times would be an example of high precision.
Certified Tutor
All GRE Subject Test: Chemistry Resources
