Chemistry Quantitative March 2018

Question 1

What is the equation of moles?

Answer 1

Moles = mass / Mr

Question 2

What does ‘Mr’ stand for?

Answer 2

Relative formula mass

Question 3

What is an excess substance?

Answer 3

A substance that there is more than we need

Question 4

What is a limiting substance?

Answer 4

It dictates the mass of the product

Question 5

What is the equation for % Yield?

Answer 5

actual mass obtained / calculated mass x 100

Question 6

What are the definitions for Yield and % Yield?

Answer 6

Yield = The amount of product formed in a reaction.

% Yield = The amount of product gained in a reaction compared to the maximum theoretical mass.

Question 7

What is the definition for atom economy?

Answer 7

A way of measuring what percentage of the mass of all atoms in the reactants ends up in the desired products.

Question 8

What is the equation for atom economy? (%)

Answer 8

Mr of desired product / Σ Mr of all reactants x 100

Σ = sum of

Question 9

If there is only 1 product what is the atom economy (%)?

Answer 9

100%

Question 10

1 dm^3 = ?

Answer 10

1 L or 1000 ml

Question 11

What is the equation for the moles of gas?

Answer 11

moles of gas = volume (dm^3) / 24

Question 12

What is the definition of concentration?

Answer 12

A measure of how much solute (solid) is dissolved in a solvent (water)

Question 13

If you have 90g of H2O, how many moles is there?

Answer 13

Mr = 2 x 1 + 16
moles = mass / Mr = 90 / 18 = 5 moles

Question 14

If you have 102 tons of O2, how many moles do you have?

Answer 14

102 tons = 102,000,000g
Mr = 16 x 2 = 32
moles = mass / Mr = 102,000,000 / 32 = 3,190,000 moles or 3.19x10^6 moles.

Question 15

If you have 4 moles or N2, how many grams do you have?

Answer 15

Mr = 2 x 14 = 28
moles = mass / Mr so mass = moles x Mr 
mass = moles x Mr = 4 x 28 = 112g

Question 16

If you have 0.02 moles of K2O, how many grams do you have?

Answer 16

Mr = 2 x 39 + 16 = 94
mass = moles x Mr = 0.02 x 94 = 1.88g

Question 17

What 3 step process is used to find the mass of an unknown?

Answer 17

Step 1: Work out number of moles of mass given
Step 2: Use balanced equation ratio to find out moles of unknown
Step 3: Turn moles of unknown into mass of unknown

e.g. How much CO2 is made when 48g of CH4 is burnt
Mr of CH4 = 12 + 4 = 16
moles = mass / Mr =  48 / 16 = 3 moles
ratio = CH4 : CO2 = 1 : 1
moles of CO2 = 3 moles
Mr of CO2 = 14 + 16 x 2 = 44
mass = moles x Mr = 3 x 44 = 132g

Question 18

How do you find the simplest ratio by using mass?

Answer 18

Find the moles of all reactants and products by using moles = mass / Mr
then divide all moles by the smallest mole. With the numbers now put them into the equation to balance it

e.g. Equation = H2O2 –> H2O + O2
Mr = 34 18 32
Mass = 6.8g 3.6g 3.2g

Moles = 6.8 / 34 & 3.6 / 18 & 3.2 / 32
= 0.2 0.2 0.1

Ratio = 0.2 / 0.1 : 0.2 / 0.1 : 0.1 / 0.1
= 2 2 1
Balanced equation = 2H2O2 –> 2H2O + O2

Question 19

What is a mole?

Answer 19

A mole is a measurement of the amount of a substance

Question 20

What is the equation for concentration?

Answer 20

Concentration = moles / volume