Amount of Substance

Question 1

What is a total ionic equation?

Answer 1

A chemical equation that shows all the ions in a reaction

Question 2

What are spectator ions?

Answer 2

Ions that don’t get involved in the reaction. They don’t change charge

Question 3

Give the ionic equation for NaOH + HCl –> NaCl + H2O

Answer 3

OH- + H+ –> H2O

Question 4

State what is meant by the term ‘relative atomic mass’

Answer 4

The average mass of an atom of an element compared to 1/12th the mass of a 12C atom

Question 5

State what is meant by the term ‘relative molecular mass’

Answer 5

The average mass of an molecule compared to 1/12th the mass of a 12C atom

Question 6

What is Avogadro’s number and what is meant by this term?

Answer 6

6.023x (10 to the power 23)

It is the number of atoms found to be in 12g o 12C

Question 7

How can you work out mass using Mr and moles?

Answer 7

Mass = Mr x moles

Question 8

How do you work out the number of molecules in a certain amount of a substance?

Answer 8

Find the moles and then times that by Avogadro’s number

Question 9

What is empirical formula?

Answer 9

The simplest ratio of atoms of each element in a compound

Question 10

What is the ideal gas equation?

Answer 10

pV=nRT

Question 11

What do the letters represent in the ideal gas equation, and what are the units for each?

Answer 11

pV=nRT
p=pressure in Pascals
V=volume in metres cubed
n=moles
R=gas constant (8.31 Jk-1mol-1)
T=temperature in Kelvin

Question 12

O*C is how many Kelvin?

Answer 12

273K

Question 13

What do you have to do to convert from cm3 to dm3?

Answer 13

divide by 1000

Question 14

What do you have to do to convert from cm3 to m3?

Answer 14

divide by 1,000,000

Question 15

Give three reasons why 100% yield may not be obtained

Answer 15

• the reaction is reversible
• some of the product is lost when it is separated from the reaction mixture
• some of the reactants may react in other reactions

Question 16

How do you calculate % yield?

Answer 16

Actual/possible x100

Question 17

State what is meant by atom economy

Answer 17

The measure of what proportion of the products of a reaction are desired and how much is waste

Question 18

What can a company do to maximise profits when a reaction has a low atom economy, without changing the reaction conditions or production costs?

Answer 18

Sell unwanted products

Question 19

How can you calculate moles from concentration and volume?

Answer 19

m = c x v