C4: Chemical Calculations

Question 1

What is a limiting reactant in a chemical reaction?

Answer 1

The chemical/element that is completely used up during the reaction

Question 2

Why can the percentage yield never be above 100%?

Answer 2

Because if the percentage yield was above 100% then there would be more product obtained than the maximum mass created.

Question 3

How do you figure out relative atomic mass of a substance/compound?

Answer 3

You multiply all the elements atomic mass by how many times they appear.

For example in H2O
H = 1 x 2 = 2
O = 16 x 1 = 16 2 + 16 = 18

Question 4

What is atom economy?

Answer 4

A measure of how efficient a chemical reaction is

Question 5

How do you calculate atom economy?

Answer 5

It is calculated by dividing the relative atomic mass of the desired product, by the total relative atomic mass of the reactants and multiplying by 100.

For example,
CO + H2O = CO2 + H2 Work out the atom economy of H2
28 + 18 = 44 + 2

2/46 x 100 = 4.35%

Question 6

H2 + O2 -> H2O

Balance this equation

Answer 6

2H2 + O2 -> 2H2O

Question 7

How do you convert between Mol/dm^3 and G/dm^3?

Answer 7

Multiply the mol/dm^3 by the Mr of the substance

Question 8

If you have 1 mole of any gas, how much dm^3 will it fill?

Answer 8

24dm^3

Question 9

What is avogrados number?

Answer 9

6.022 x 10^23

Question 10

What is a mole?

Answer 10

The amount of substance that contains 6.022 x 10^23 particles of that type of substance

Question 11

How do you calulate % yield?

Answer 11

Actual mass obtained

divided by

The theoretical mass too be obtained