why is the copper/sulfur mass ratio different from the mole ratio?

The copper/sulfur mass ratio can be different from the mole ratio due to the differing atomic masses of copper and sulfur.

To understand why this happens, let's start by discussing the mole ratio and atomic masses. The mole ratio is the ratio of the number of moles of one substance to another in a chemical reaction. It can be determined from the balanced chemical equation.

For example, consider the reaction between copper (Cu) and sulfur (S) to form copper(I) sulfide (Cu2S):

2Cu + S → Cu2S

From the balanced equation, we can see that the mole ratio between copper and sulfur is 2:1. This means that for every 2 moles of copper, 1 mole of sulfur is required.

However, when we consider the mass ratio, we need to take into account the atomic masses of copper and sulfur. Copper has an atomic mass of around 63.55 grams/mol, while sulfur has an atomic mass of around 32.07 grams/mol.

Let's say we have 63.55 grams of copper. To calculate the mass of sulfur required to react with this amount of copper, we can use the mole ratio from the balanced equation.

63.55 grams of copper * (1 mole of sulfur / 2 moles of copper) * (32.07 grams of sulfur / 1 mole of sulfur) = 102.52 grams of sulfur

In this example, we can see that the mass ratio of copper to sulfur is approximately 1:1.61. This is different from the mole ratio of 2:1.

Therefore, the copper/sulfur mass ratio can be different from the mole ratio due to the differing atomic masses of copper and sulfur, which affects the number of atoms or molecules present in a given mass of each element.