1 - 2 Principles of Chemistry

Question 1

What does aqueous mean?

Answer 1

Dissolved in water

Question 2

What are isotopes?

Answer 2

An element that has the same number of protons but different numbers of neutrons
- Same proton number but different mass numbers

Question 3

What is the relative atomic mass?

Answer 3

Says how heavy the atom is compared with the mass of an atom of carbon-12 (Ar)

Question 4

How do you work out the relative atomic mass?

Answer 4

• State the mass of the isotopes
• State the relative abundance
• Multiply the mass by the relative abundance
• Add together
• Divide by the sum of the relative abundances

Question 5

What is the relative abundance?

Answer 5

How much there is of each isotope compared to the total amount of element in the world
- Can be a fraction, percentage or ration

Question 6

How do you work out the relative formula mass?

Answer 6

(Mr)

• Add the atomic mass together
• If there is more than one multiply (e.g. MgCl2 - multiply Cl by 2)

Question 7

How do you work out the empirical formula?

Answer 7

• List all the elements in the compound
• Underneath write their experimental masses or percentages
• Divide each mass or percentage by the relative atomic mass (Ar) for each element
• Turn the numbers into a ratio
• Put the ratio in the simplest form

Question 8

How do you work out the empirical formula?

Answer 8

• List all the elements in the compound
• Underneath write their experimental masses or percentages
• Divide each mass or percentage by the relative atomic mass (Ar) for each element
• Turn the numbers into a ratio
• Put the ratio in the simplest form

Question 9

What is the empirical formula?

Answer 9

The simplest formula that tells you the ratio of different elements in the compound
The mass number tells you the actual number of each element

Question 10

What is the equation for the percentage yield?

Answer 10

Actual yield (grams) / theoretical yield (grams) x100

Question 11

How do you calculate masses in reactions>

Answer 11

• Write out the balanced equation
• For the two bits you want, work out the relative formula mass and multiply by the balancing numbers in the equation
• Divide to get one
• Multiply to get all

Question 12

What is the equation for the number of moles?

Answer 12

m = M / Mr
moles = mass (g) / Mr

Question 13

What is the name of water in a lattice?

Answer 13

Water of crystallisation

Question 14

What is the name of water in a lattice?

Answer 14

Water of crystallisation

Question 15

Describe how to work out the amount of water lost in a salt

Answer 15

• Work out the mass (with and without)
• Calculate the number of water lost in moles (mass/Mr)
• Calculate the amount of anhydrous salt lost in moles
• Work out the ratio of made to lost
• Divide to find 1 mole
• Round to the nearest whole number

Question 16

What is the equation for volume of a gas?

Answer 16

volume (dm3) = moles x 24

Question 17

What is the ratio of dm3 to cm3?

Answer 17

1dm3 = 1000cm3

Question 18

What is the equation for concentration?

Answer 18

Concentration (mol/dm3) = moles / volume

Question 19

How do you change mol/dm3 to g/dm3?

Answer 19

• Work out the relative formula mass
• Mass = mol x relative formula mass
• Divide by how many moles you want

Question 20

How do you change mol/dm3 to g/dm3?

Answer 20

• Work out the relative formula mass
• Mass = mol x relative formula mass
• Divide by how many moles you want

Question 21

What is the electricity flow?

Answer 21

The flow of electrons or ions

Question 22

When do ionic compounds conduct electricity?

Answer 22

• Only when it is molten or in a solution as the electrons are free to move around

Question 23

Do covalent compounds conduct electricity?

Answer 23

• No because they don’t contain ions as they’re electrons are shared
• No carriers free to move to create an electric current

Question 24

How are metals held together?

Answer 24

• By metallic bonding
• Have a giant structure of positive electrons surrounded by delocalised electrons
• Good conductors of heat and electricity
• Most are malleable as atoms can slide over each other meaning they can be hammered or rolled into flat sheets

Question 25

How are metals held together?

Answer 25

- By metallic bonding - Have a giant structure of positive electrons surrounded by delocalised electrons - Good conductors of heat and electricity - Most are malleable as atoms can slide over each other meaning they can be hammered or rolled into flat sheets

Question 26

What is electrolysis?

Answer 26

- Used to make a new substance - Works by passing an electric current through an ionic substance that's molten or in solution and breaking it into new substances - Needs an electrolyte - As ions gain or lose electrons they become atoms and molecules

Question 27

What is an electrolyte?

Answer 27

- The liquid in electrolysis - Made by melting or dissolving ionic compounds - It is the free ions that conduct the electricity

Question 28

Describe electrolysis of molten lead

Answer 28

Electrolyte - molten lead bromide Electrodes - carbon Anode - Bromine is produced (2Br- --> Br2 + 2e-) Cathode - Lead is produced (Pb2+ + 2e- --> Pb)

Question 29

Describe electrolysis of molten lead

Answer 29

Electrolyte - molten lead bromide Electrodes - carbon Anode - Bromine is produced (2Br- --> Br2 + 2e-) Cathode - Lead is produced (Pb2+ + 2e- --> Pb)

Question 30

Electrolysis of an aqueous solution

Answer 30

Hydrogen and hydroxide ions will be produced

Question 31

What happens at the cathode in electrolysis of an aqueous solution?

Answer 31

If H+ ions and metal ions are present: - A more reactive metal ion will produce hydrogen gas will be produced - A less reactive metal ions a solid layer of pure metal will be produced

Question 32

What happens at the anode in electrolysis of an aqueous solution?

Answer 32

- If OH- and halide ions are present halogen molecules will be formed - If no halide ions are present oxygen will be present

Question 33

Describe electrolysis of sulphuric acid

Answer 33

- Hydrogen ions (from the water or sulphuric acid) accept electrons - At the cathode hydrogen gas is produced (2H+ +2e- --> H2) - Hydroxide ions lose electrons more easily than sulphate ions - At the anode oxygen and water are produced ( 4OH- --> O2 + 2H2O + 4e-)

Question 34

Describe electrolysis of sodium chloride

Answer 34

- Hydrogen ions accept electrons more easily than sodium ions - At the cathode hydrogen gas is produced (2H+ + 2e- --> H2) - Chloride ions lose electrons more easily than hydroxide ions - At the anode chlorine gas is produced (2Cl- --> Cl2 + 2e-)

Question 35

Describe electrolysis of sodium chloride

Answer 35

- Hydrogen ions accept electrons more easily than sodium ions - At the cathode hydrogen gas is produced (2H+ + 2e- --> H2) - Chloride ions lose electrons more easily than hydroxide ions - At the anode chlorine gas is produced (2Cl- --> Cl2 + 2e-)

Question 36

Describe electrolysis of copper(III) sulphate

Answer 36

- Copper ions accept electrons more easily than hydrogen ions - At the cathode copper metal is produced (Cu2+ + 2e- --> Cu) - Hydroxide ions lose electrons more easily than sulphate ions - At the anode oxygen and water are produced (4OH- --> O2 + 2H2O + 4e-)

Question 37

How can you increase the amount of product made?

Answer 37

- Increase the number of electrons - Electrolysing for longer - Increasing the current

Question 38

How do you calculate masses in electrolysis?

Answer 38

- Write out the balanced half equation - Calculate the number of faradays (charge = current x time, charge / 96000) - Calculate the number of moles (faradays / number of electrons) - Mass = Mr x moles)