ย 

Mass calculations for SQA Higher Chemistry

Mass calculations

This page covers the following topics:

1. Theoretical mass
2. Atom economy

Due to incomplete reactions, when experiments are carried out there is not a 100% yield of products. The theoretical yield is the amount of product you could produce theoretically. The percentage yield is a measure of the amountthe actual yield you get from an experiment.

Theoretical mass

Atoms are not gained or lost in a chemical reaction, some atoms from the reactants end up in the product, and some in by-products. The atom economy of a reaction expresses how efficiently a reaction makes use of reactant atoms, i.e. how much product is creating in comparasion to by-product. Atom economy is a percentage, thus the highest it can possibly be is 100%.

Atom economy

1

What is the definition of atom economy?

A measure of the amount of starting elements/compounds that end up as useful products.

What is the definition of atom economy?

2

3 g of Cโ‚ƒHโ‚‡OH has reacted with an excess of CHโ‚ƒCOOH (Ar = 60 g/mol) to give 1.8 g of Cโ‚ƒHโ‚‡OOCCHโ‚ƒ (Ar = 102 g/mol) and some water, what is the actual yield of this reaction?

Actual yield is the experimental mass of the product.

1.8 g

3 g of Cโ‚ƒHโ‚‡OH has reacted with an excess of CHโ‚ƒCOOH (Ar = 60 g/mol) to give 1.8 g of Cโ‚ƒHโ‚‡OOCCHโ‚ƒ (Ar = 102 g/mol) and some water, what is the actual yield of this reaction?

3

What is the theoretical yield?

The maximum possible mass of product you could produce from a reaction

What is the theoretical yield?

4

What is the actual yield?

The actual yield is the final mass of product produced in a reaction.

the actual mass of product yielded in a reaction

What is the actual yield?

5

The percentage yield of the production of Cu from 6.5 g of Zn is 75%. Use the reaction equations provided to find the mass of copper produced.

Zn + CuSOโ‚„ โ†’ ZnSOโ‚„ + Cu

1 : 1 mole ratio
6.5 รท 65.38 = 0. 099 mol
0.1 ร— 63.55 = 6.32 g
6.4 ร— 0.75 = 4.74 g

4.74 g

The percentage yield of the production of Cu from 6.5 g of Zn is 75%. Use the reaction equations provided to find the mass of copper produced.

Zn + CuSOโ‚„ โ†’ ZnSOโ‚„ + Cu

End of page

ย