t4- chemical changes

Question 1

In electrolysis, why does the compound you’re trying to separate need to be molten or dissolved?

Answer 1

So that the ions are free to move around (and go to their respective electrode)

Question 2

What is the molten/dissolved substance in electrolysis called?

Answer 2

electrolyte

Question 3

what are 2 chemical processes are used to extract metals from their ores?

Answer 3

electrolysis, reduction with carbon

Question 4

how is a metal extracted from an ore in electrolysis?

Answer 4

electricity is used to split the compound into its elements

Question 5

Why is electrolysis not used to extract all metals?

Answer 5

it’s expensive because it needs lots of electricity

Question 6

What is the name of the substance that is mixed with aluminium oxide to lower its melting point?

Answer 6

cryolite

Question 7

In the electrolysis of aqueous solutions, how do you determine which ion will be oxidised at the anode?

Answer 7

it will always be the oxygen, unless there is a halide ion present

Question 8

In the electrolysis of aqueous solutions, how do you determine which ion will be reduced at the cathode

Answer 8

It will always be the H+ ion, unless Cu2+ is present

Question 9

how can you improve the accuracy of titrations?

Answer 9

repeat the experiment until you get concordant results and calculate the mean of the concordant results

Question 10

how can metals less reactive than carbon get extracted?

Answer 10

reduction with carbon.
carbon displaces the metal in a metal oxide and gets oxidised into carbon oxides
metal from the metal oxide gets reduced into pure metal

Question 11

equation for reaction of metals with acids

Answer 11

redox reaction
metal + acid -> salt+ hydrogen

Question 12

equation for neutralisation reaction

Answer 12

base + acid -> salt + water

Question 13

equation for reaction between metal carbonate and acid

Answer 13

metal carbonate+ acid -> salt + water + carbon dioxide

Question 14

equation for reaction between metal oxides/hydroxides and acids

Answer 14

acid + metal oxide/hydroxide -> salt + water

Question 15

what is a redox reaction

Answer 15

reaction where oxidation and reduction occurs

Question 16

how to form a soluble salt

Answer 16

1. measure acid into beaker
2. heat gently
3. add spatulas of metal oxide and stir until metal oxide is in excess
4. filter out excess with filter funnel and filter paper
5. heat remaining solution in evaporating basin until crystallisation point
6. leave it to form crystals, then dry off with filter paper

Question 17

how to perform titration

Answer 17

1. measure acid into conical flask
2. measure solution into burette
3. put white tile under flask and put it under burette
4. open tap slowly, add it drop-wise until there’s a colour change
5. read volume on burette
6. repeat this and compare results

Question 18

what do acids and alkalis produce in aqueous solutions

Answer 18

acids- H+ ions
alkalis- OH- ions

Question 19

general ionic equation for neutralisation reaction

Answer 19

H+ + OH- -> H2O

Question 20

what is a strong acid

Answer 20

completely ionised in aqueous solution

Question 21

what is a weak acid

Answer 21

partially ionised in aqueous solution

Question 22

what happens to ph as concentration of H+ ions increases

Answer 22

ph decreases

Question 23

what is concentrated acid

Answer 23

has more moles of acid per unit volume

Question 24

what is cathode, what is anode

Answer 24

cathode= negative electrode
anode= positive electrode

Question 25

what occurs at cathode and anode during electrolysis

Answer 25

reduction at cathode
oxidation at anode

Question 26

in aqueous electrolysis, which element is discharged at cathode

Answer 26

less reactive element discharges at cathode

Question 27

how is aluminium manufactured

Answer 27

through the electrolysis of aluminium oxide and cryolite
lots of energy is needed to produce the electric current, so it’s expensive