C4: Quantitative Chemistry

Question 1

What is the equation for number of particles?

Answer 1

Number of Particles = Moles x 6.023x10^23 (Amount of atoms in one mole of a substance)

Question 2

What is the equation linking moles, mass and Mr?

Answer 2

Moles = Mass (g) / Mr (g/mol)

Question 3

Why might law of conservation of mass be broken?

Answer 3

If one of the reactants or products is a gas then the mass won’t be equal.

Question 4

Why do we balance equations?

Answer 4

To make sure the numberof moles of each element is the same on both sides. Can be used to find masses of reactants/products.

Question 5

What is the limiting reactant?

Answer 5

The reactant that gets used up first in a reaction and is not in excess. It determines the amount of product formed.

Question 6

What is the percentage yield equation?

Answer 6

Percentage Yield = Actual Mass of Product Produced / Theoretical mass Produced x 100

Question 7

What are the factors affecting percentage yield?

Answer 7

• If the reaction is reversible.
• Reactants may give unwanted products in alternative reactions.
• Some of product may be lost in handling or left in apparatus.
• Some of desired product may be lost during separation.

Question 8

What is the % atom economy equation?

Answer 8

% Atom Economy = Mr of Desired Product / Sum of Mr of Reactants x 100

Question 9

Why is it important to maximise atom economy?

Answer 9

In industrial processes it is important to conserve the Earth’s resources and minimise pollution. It would be better economically and more efficient means less waste.

Question 10

What are the equations for concentration?

Answer 10

Concentration (g/dm3) = Mass of Solute (g) / Volume of Solution (dm3)

Concentration (mol/dm3) = Moles (mol) / Volume (dm3)

Question 11

What is the purpose of titration?

Answer 11

It is used to measure what volumes of acid and alkali react together completely and neutralise.

Question 12

What is the equation for volume of gas?

Answer 12

Volume of Gas (dm3) = Moles x 24dm3

Question 13

How do you carry out titration between sodium hydroxide (alkali) and sulphuric acid?

Answer 13

1. Use pipette to measure 25cm3 of sodium hydroxide into a conical flask and place it onto a white tile.
2. Fill burette with sulphuric acid using a funnel, making sure it was rinsed before. Record the initial acid volume in the burette.
3. Add a few drops of indicator to the conical flask.
4. Slowly open the burette tap to allow acid into conical flask and swirl.
5. Close burette when colour change occurs as the alkali is neutralised.
6. Record final reading of acid in burette and calculate titre - volume of acid used to neutralise acid.
7. Repeat until you have concordant result within 0.1 of each other and calculate mean titre.