You have a 10.0 g sample of gallium-68. Half of it decays in 68.3 minutes. How much will be left after two half-lives? Make sure to round to the correct number of significant figures and use units (g)

814 g

Explanation:

Let's consider the following reaction.

2 ZnO + C → 2 Zn + CO₂

The molar ratio of ZnO to C is 2:1. The moles of ZnO required to react with 5.00 mol of C are:

5.00 mol C × (2 mol ZnO/1 mol C) = 10.0 mol ZnO

The molar mass of ZnO is 81.38 g/mol. The mass corresponding to 10.0 moles is:

10.0 mol × 81.38 g/mol = 814 g