chemical changes

Question 1

What do acids, alkalis and neutral substances look like on the pH scale?

Answer 1

Strong acids are red, weak acids are orange-yellow, neutral substances are green, weak alkalis are blue and strong alkalis are purple

Question 2

Name a strong acid

Answer 2

car battery acid, hydrochloric acid

Question 3

Name a strong alkali

Answer 3

caustic soda (drain cleaner), bleach

Question 4

What is a neutralisation reaction?

Answer 4

The reaction between acids and bases

Question 5

What is the general formula for a neutralisation reaction?

Answer 5

acid + base > salt + water

Question 6

What is an acid?

Answer 6

A substance that forms and aqueous solution with a pH lower than 7

Question 7

What is an alkali?

Answer 7

A substance that dissolves in water to form a solution with a pH greater than 7

Question 8

How does a neutralisation reaction work?

Answer 8

H+ ions and OH- ions react to form H2O, giving the substance a PH of 7

Question 9

What ions do acids and bases form in water?

Answer 9

acids form H+ ions and alkalis form OH- ions

Question 10

Describe the titration required practical?

Answer 10

1. Use a pipette and pipette filer to add a set volume of alkali to a conical flask and add a few drops of phenolphthalein
2. Fill a burette with an acid of known concentration below eye level and record the initial volume
3. use the burette to add small amounts of acid at a time, swirling regularly
4. Once the mixture is colourless, record the final volume of acid and calculate the amount of acid used then repeat the experiment for accuracy

Question 11

Why should you use single indicators in titrations?

Answer 11

single indicators such as phenolphthalein, litmus and methyl orange do not have a range of colours and therefor neutralisation isn’t subjective

Question 12

Why and how should you repeat a titration?

Answer 12

The first should be a rough titration to get a rough idea of the end point and then repeat until the results are within 0.1cm^3 to ensure accuracy and precision

Question 13

What is a strong acid?

Answer 13

An acid that ionises completely in water, all the particles dissociate to release H+ ions

Question 14

What is a weak acid?

Answer 14

Acids that do not fully ionise in solution, only a small proportion of particles dissociate to form H+ ions

Question 15

What does pH measure?

Answer 15

the concentration of H+ ions in a solution

Question 16

What is the relationship between pH and concentration of H+ ions?

Answer 16

the factor H+ ion concentration changes by is equal to 10^-x ( x is the difference in pH)

Question 17

What do metal oxides and metal hydroxides form when reacted with acid?

Answer 17

salt and water as they are both neutralisation reactions

Question 18

Are metal oxides and metal hydroxides acids or bases?

Answer 18

Bases

Question 19

Are metal carbonates acids or bases?

Answer 19

Bases

Question 20

What is produced when acids and metal carbonates react?

Answer 20

salt, water and carbon dioxide

Question 21

Describe the making soluble salts using an insoluble base required practical?

Answer 21

1. Pick a suitable acid and an insoluble base e.g. insoluble metal hydroxide, oxide or carbonate
2. Gently warm the dilute acid using a Bunsen burner
3. Add the base to the acid until the base is in excess. You will see excess solid sink to the bottom of the flask
4. Filter out excess solid to get the salt solution and then use crystallisation to extract the salt crystals

Question 22

What is the reactivity series?

Answer 22

A list of metals in order of their reactivity towards other substances

Question 23

What is the reactivity series from least to most reactive?

Answer 23

Copper, iron, zinc, magnesium, calcium, lithium, sodium, potassium

Question 24

Which metals in the reactivity series are more reactive than carbon?

Answer 24

magnesium, calcium, lithium, sodium, potassium

Question 25

Which metal on the reactivity series won't react with acids and why?

Answer 25

Copper will not react with acids as it is less reactive than hydrogen

Question 26

What is produced when an acid and a metal react?

Answer 26

salt and hydrogen

Question 27

What is produced when metal reacts with water?

Answer 27

metal hydroxide and hydrogen

Question 28

Which metals will react with water and which won't?

Answer 28

Potassium, sodium, lithium, calcium will react with water, zinc, iron and copper will not

Question 29

What is oxidation and reduction in terms of oxygen?

Answer 29

Oxidation is oxygen gain and reduction is oxygen loss

Question 30

What is a reduction reaction?

Answer 30

A reaction that separates a metal from its oxide

Question 31

How does carbon reduction work?

Answer 31

The ore is reduced as oxygen is removed from it, bonding to carbon, oxidising it

Question 32

Which metals can be extracted using carbon reduction?

Answer 32

Zinc, iron and copper

Question 33

What is the advantage of carbon reduction?

Answer 33

Cheaper than electrolysis

Question 34

What is oxidation and reduction in terms of electron transfer?

Answer 34

Oxidation is loss of electrons and reduction is gain of electrons

Question 35

What is a redox reaction?

Answer 35

A reaction where both reduction and oxidation occur

Question 36

What is a displacement reaction?

Answer 36

A reaction in which a more reactive element replaces a less reactive element in a compound

Question 37

What is electrolysis?

Answer 37

Splitting apart an ionic compound using electricity

Question 38

What are the positive and negative electrodes called?

Answer 38

Positive- anode negative-cathode

Question 39

At which electrodes do reduction and oxidation occur?

Answer 39

Reduction occurs at the cathode, oxidation occurs at the anode

Question 40

Describe what happens to positive ions at the cathode?

Answer 40

Positive ions (missing electrons), gain electrons at the cathode to become atoms again

Question 41

Describe what happens to negative ions at the anode?

Answer 41

Negative ions (with extra electrons), lose electrons to become atoms again

Question 42

Why should the electrodes be inert?

Answer 42

So that they do not react with the electrolyte

Question 43

What is an electrolyte?

Answer 43

A molten or dissolved ionic compound to be used in electrolysis

Question 44

Why must ionic compounds be molten or aqueous in order for electrolysis to occur?

Answer 44

The ions can move freely, allowing them to carry charge

Question 45

What will form at the anode and the cathode in molten solutions?

Answer 45

Metals will be produced at the cathode, non metals will be produced at the anode ( oxygen)

Question 46

What is cryolite and why is it used?

Answer 46

Cryolite lowers the melting point of metals so that less energy is required to melt the compounds

Question 47

What will be formed at the cathode in the electrolysis of aqueous solutions?

Answer 47

If the metal is more reactive than hydrogen, hydrogen gas bubbles will be produced. If the metal is less reactive than hydrogen (copper), a solid layer of pure metal will be produced

Question 48

What will be formed at the anode in the electrolysis of aqueous solutions?

Answer 48

If halide ions are present (Br, Cl, I), their gas forms ( bromine gas, chlorine gas etc) will form. If no halide ions are present, oxygen gas and water will form

Question 49

What is the test for chlorine?

Answer 49

Chlorine bleaches damp litmus paper, turning it white

Question 50

What is the test for hydrogen?

Answer 50

Hydrogen makes a squeaky pop with a lighted splint

Question 51

What is the test for oxygen?

Answer 51

Oxygen relights a glowing splint?

Question 52

How would you test if a gas was formed during electrolysis?

Answer 52

Collect the gas at the electrode using a test tube and test for the gas.