Help with chem questions...?

Question

A 1.000 mL sample of acetone was places in small bottles whose mass was know to be 38.0015g. The following three values were obtained when the acetone filled bottle was weighed : 38.7799g, 38.7800g and 38.7804g. If the actual mass of the acetone was 0.7791 g, how would you characterize the precision and accuracy of the measurements.

2.) An expiriment requires 23.0 g of sulfuric acid, a liquid whose density is 1.831 g/mL. Rather than weigh the sample on a balance a student chooses to dispense the liquire using a graduated cylander. Calculate the volume in milliliters of sulfuric acid that should be measured.

Answer 1

1. calculate the masses of acetone collected

      38.7799 - 38.0015 = 0.7784 g

      38.7800 - 38.0015 = 0.7785 g

      38.7804 - 38.0015 = 0.7789 g

Precision is how close the results are to each other, so your values are 0.77865 +/- 0.00025 g, which is reasonably precise.

Accuracy is how close an individual answer is to the correct answer, so your first 2 measurements are less accurate than the last.

2. 23.0 g / 1.831 g/mL = 12.56 mL

Answer 2

38.7802 (ave)   -   38.0015g = 0.7787

your 0.7787 average varies in the last sigfig from the actual 0.7791, that is great accuracy

your answers vary from them selves in 0.0005, in the last sig fig, that  is great precision

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23.0 g @ 1 ml / 1.831 g = 12.56ml

your answer is 12.6 ml

Answer 3

A. Analytical...not my forte, hopefully someone else can answer.

2. 12.6 mL, if maintaining significant figures.