Question

how to calculate the number of iron added

Answer 1

To find the number of moles of Fe…

Given: Number moles = mass (in g) / molar mass (g/mole)

Molar mass of Fe = 55.8g (3 sig fig)

Number of moles of Fe = 1.94 / 55.8 = 0.0348 moles to 3 sig figs

To find the number of moles of CuSO4…

Molar mass of CuSO4 = 63.5 + 32 + 16x4 = 159.5 to 4 sig fig (as per quote in your question)

Number moles CuSO4 = 14.00 / 159.5 = 0.08777 to 4 sig figs

As your least accurate value is to 3 sig figs, that is the limit of accuracy for this calculation, therefore there are 0.0878 moles of CuSO4

As the reaction quatities are 1:1, it is to be deduced that all of the Fe is used up…

Amount of CuSO4 remaining = 0.0878 - 0.0348 = 0.0530 moles of CuSO4.