Chemistry 122 d

Question

Calculate the mass of 8.5 x 10-2 mol calcium nitrate

Answer 1

The chemical formula for calcium nitrate is Ca(NO₃)₂

To find one mole of calcium or the molar mass, we must multiply the mass of an individual element with the subscript and take the sum of the mass of all these elements. Calcium has no subscript so there is only one atom of calcium. There are 2 atoms of nitrogen and then 6 atoms of oxygen because 3*2 = 6.

Mass of each individual element in grams:

Calcium - 40.08 g

Nitrogen - 14.01 g

Oxygen - 16.00 g

To calculate one mole of Ca(NO₃)₂ : (40.08 g * 1 atom of Calcium) + (14.01 g * 2 atoms of Nitrogen) + (16.00 g * 6 atoms of Oxygen) = 164.1 grams per mole or 164.1 g/mol

Use stoichiometry or dimensional analysis to find the mass of 8.5 x 10^-2 moles of Ca(NO₃)₂ :

8.5 x 10^-2 mol * 164.1 g/mol = 13.9485 grams ~ 14 g (using 2 significant figures)