Analytical Chemistry Answers

Analytic Chemistry

1. Use the given choices below to describe the set of data collected. Data is determined to be accurate if the % error is ≤ 5.00% and precise if the SD ≤ 0.10.

Length measurements of a 1.00 ft ruler were recorded as follows: 12.0 inches, 11.9 inches, 12,1 inches

A. precise only

B. accurate only

C. neither accurate nor precise

d. both accurate and precise.

2.Use the given choices below to describe the set of data collected. Data is determined to be accurate if the % error is ≤ 5.00% and precise if the SD ≤ 0.10.

Mass measurements of a 10.00 g standard collects the following masses after three trials: 10.99, 10.98, 10.99

A. precise only

B. accurate only

C. neither accurate nor precise

d. both accurate and precise.

. You calibrate a 100 mL volumetric flask by weighing the water it contains. At the 

temperature of the measurement, the density of water is 0.997 906 ± 0.000 111 g/mL. 

(This uncertainty is due to random fluctuations in the ambient temperature.) The 

buoyancy correction factor mtrue/mread = 1.001 053; its uncertainty is negligible. Write all 

values and uncertainties in this problem with one guard digit. [Throughout this exam, 

you may type “+/-” for ± and use an underscore to indicate subscripts: “+/- 0.003_3” 

for 0.0033.]

__/3 a. After performing several replicate measurements, you determine that the average 

uncorrected mass of water contained by the flask is 99.7562 ± 0.0033 g. Calculate 

the true mass of the water. [Ignore uncertainties until part c.]

__/3 b. Now calculate the calibrated volume of the flask in mL.

__/3 c. Which quantity has the larger absolute uncertainty? Briefly explain your choice.

density cannot be compared [uncorrected] mass

__/3 d. Which quantity contributes more to the uncertainty in the volume? Report the 

numbers you compared to reach your answer.

density cannot be compared [uncorrected] mass

__/6 e. Propagate these uncertainties to determine the uncertainty in the calibrated volume, 

and report the volume of the flask (in mL) as you would an intermediate result. [If 

you could not answer part b use 99.999 999... mL instead.]

__/4 f. Rewrite your answer from e in L. Which numeric value should remain the same when 

you multiply or divide by an exact conversion factor, the relative uncertainty or the 

bsolute uncertainty?

__/2 g. What would the relative uncertainty of the volume be if you thermostatted the water 

to eliminate the temperature fluctuations and thus the uncertainty in its density?

[You should have calculated this value earlier in this question.]

A 1.00 ml alioquot of fish oil (ammonia) was analyzed for nitrogen. After digestion the distilled

ammonia was collected in 100.00 ml of 0.05030 M HCl. The excess HCl required 28.30 ml of 0.1240 M

NaOH for titration. Calculate the amount (in moles and grams) of N in the sample.

A student did an experiment to determine the specific heat capacity of a metal alloy. The student put a sample of the alloy in boiling water for several minutes, then quickly transferred the alloy into a calorimeter containing water originally at . The temperature of the water was monitored over time. The data are given in the graph above.

(a) What is the value of delta T that the student should use to calculate the value of q , the heat gained by the water?

b) In terms of what occurs at the particulate level, explain how the temperature of the water increases after the alloy sample is added.

c) The student claims that thermal equilibrium is reached at time . Justify the student’s claim. In your justification, include a description of what occurs at the particulate level when the alloy and the water have reached thermal equilibrium.