Can someone check my answers? Thanks.
1.) If you were involved in an acid rain monitoring project with several other samplers, why would it be important that all of you collect your samples on the same day and do the alkalinity tests within 24 hours?
Acid rain on another day may not have the same pH as the rain on that day. The pH may also decrease over time.
2.) A student did an alkalinity determination correctly, except that the sample titrated had a volume of 90.0 mL. Volume A was found to be 4.50 mL and Volume B was 7.00 mL.
a)Calculate the alkalinity value from these data and then calculate the correct value.
A=(2A-B)
A=(2(4.50-7.00)=2.0 mL^-1
A=(2(4.545)-7.07)
answer = 2.02mL^-1
b)What percent error would there be?
2.02-2.0
--------
2.02
x100
answer = .99%
c) Would there be an error in the classification of the stream? Explain concisely.
There would not have been an error in the classification. It was just a measurement error in this case.
3) EPA acidity tests can be performed by titrating a water sample to a pH of 8.2. What titrant in what concentration would you suggest for EPA acidity determinations?
The titrant I would suggest for EPA acidity determinations is sulfuric acid under a standard concentration.
1) It is important for all samplers in an acid rain monitoring project to collect their samples on the same day and perform alkalinity tests within 24 hours because the pH of acid rain can vary from day to day. By collecting samples on the same day, you can ensure that you are all measuring the acidity of the same rainfall event. Additionally, the pH of acid rain can change over time as it interacts with various substances in the atmosphere and on the ground. By testing the alkalinity within 24 hours, you can minimize the potential changes in pH that could occur if the samples are left for longer periods of time.
2a) To calculate the alkalinity value, you can use the formula A = 2A - B, where A is the volume A (4.50 mL) and B is the volume B (7.00 mL). Substituting the values into the equation, you get A = 2(4.50) - 7.00 = 2.00 mL^-1. However, the correct value is calculated as A = 2A - B = 2(4.545) - 7.07 = 2.02 mL^-1.
b) To calculate the percent error, you can subtract the correct value (2.02) from the obtained value (2.00), divide the difference by the correct value (2.02), and then multiply by 100. So, the percent error is (2.02 - 2.00) / 2.02 * 100 = 0.99%.
c) In this case, there would not be an error in the classification of the stream. The measurement error in the alkalinity determination does not affect the classification of the stream. The classification is based on the established thresholds and criteria, not just a single measurement.
3) For EPA acidity determinations, sulfuric acid would be a suitable titrant. The exact concentration would depend on the specific requirements and sensitivity of the test. However, it is important to use a standardized concentration to ensure accurate and consistent results. The concentration should be chosen such that it allows for the detection and measurement of acidity in the water sample being tested.