Question

How many grams of hydrochloric acid will react completely with a block of gold that is 3.2 cm by 3.8 cm by 2.8 cm, if the density of gold is 19.3 g/ml?

Answer 1

The chemical reaction would be:

2Au + 2HCl = 2AuCl + H2

First, we need to determine the mass of gold that is used in the reaction. We do this by multiplying the volume of the block of gold to its density. We do as follows:

Mass of Au = (3.2 cm) (3.8 cm) (2.8 cm) ( 1 mL / 1 cm^3) ( 19.3 g/ mL) = 657.1264 g Au

From the molar mass of Au which is 197 g/mol, we convert the mass of Au to moles and relate HCl by using the balanced reaction. We do as follows:

657.1264 g Au ( 1 mol / 197 g ) ( 2 mol HCl / 2 mol Au ) ( 36.46 g / mol ) = 121.62 g HCl