Question

Question 1

A Chem 2111 student in a gravimetric analysis experiment analyzed an iron ore by dissolving a 1.1234 g sample in concentrated HCl solution. After dilution with water, the iron(III) in the sample was precipitated as Fe₂O₃.xH₂O by addition of ammonia NH₃. After filtration, washing and drying, the precipitate was isolated to produce 0.5394 g of pure Fe₂O₃.

a) Calculate the weight percent of iron Fe in this sample.

b) Calculate the weight percent of magnetite Fe₃O₄ (rock mineral) in this sample using the chemical equation below.

Fe₂O₃ --> Fe₃O₄ + O₂ (unbalanced).

Question 2

Consider the following arithmetic calculation: ([14.3(± 0.2) - 11.6(± 0.2)] x 0.050(± 0.001)) / ([820(± 10) + 1030(± 5)] x 42.3(± 0.4)) = ?

a) Calculate the percent relative uncertainty.

b) Calculate the absolute uncertainty.

c) Give the final answer of this calculation with the correct number of significant figures, including the proper number of digit in the absolute uncertainty

Answer 1