C3 Chemical changes

Question 1

What ions does an acid form in solutions?

Answer 1

H+ ions

Question 2

What ions does a base have?

Answer 2

OH- ions

Question 3

What is a base?

Answer 3

any substance + acid –> salt + water

Question 4

What is an alkali?

Answer 4

• a soluble base
• that dissolves in water
• form OH- ions

Question 5

What colour changes occur on red litmus paper?

Answer 5

acidic solution - red
neutral solution - red
alkaline solution - blue

Question 6

What colour changes occur on blue litmus paper?

Answer 6

acidic solution - red
neutral solution - blue
alkaline solution - blue

Question 7

What colour changes occur on litmus paper?

Answer 7

acidic solution - red
neutral solution - purple
alkaline solution - blue

Question 8

What colour changes occur in methyl orange?

Answer 8

acidic solution - red
neutral solution - yellow
alkaline solution - yellow

Question 9

What colour changes occur in phenolphthalein?

Answer 9

acidic solution - colourless
neutral solution - colourless
alkaline solution - pink

Question 10

What is a neutral pH?

Answer 10

7

Question 11

What is an acidic pH?

Answer 11

1-6

Question 12

What is an alkaline pH?

Answer 12

8-11

Question 13

How does the concentration of H+ ions affect pH?

Answer 13

high conc means lower pH

-more acidic

Question 14

How does concentration of OH- ions affect pH?

Answer 14

high conc means higher pH

-more alkaline

Question 15

How does H+ ion concentration in a solution affect pH?

Answer 15

As H+ ion conc increases by a factor of 10 pH decreases by 1

eg pH 5 x10H+ —> pH 4

Question 16

If the pH decreases what has happened to the H+ ion concentration?

Answer 16

increased by a factor of 10

Question 17

How is concentration different to acid strength?

Answer 17

concentration
-how much acid that is dissolved in 1 dm^3 of water

acid strength
-how much of the acid dissociates to form H+ ions

Question 18

What is a strong acid?

Answer 18

strong acids completely ionise in water

-> dissociate to release H+ ions

Question 19

What is a weak acid?

Answer 19

weak acids partially ionise in water
-> some molecules dissociate

ionisation of a weak acid is reversible

Question 20

What makes an acid dilute?

Answer 20

if there is not a lot of acid in the solution

Question 21

What makes an acid concetrated?

Answer 21

if there is a lot of it in the solution

Question 22

What is the reaction between a base and acid?

Answer 22

• neutralisation
• salt and water formed only
• water has neutral pH of 7

Question 23

How do you test for hydrogen?

Answer 23

• lighted splint

- squeaky pop

Question 24

How do you test for carbon dioxide?

Answer 24

• bubble gas through limewater

- turns cloudy white

Question 25

What products form from reacting a metal and acid?

Answer 25

metal + acid —> metal salt + hydrogen

Question 26

What products form from reacting a metal oxide and acid?

Answer 26

metal oxide + acid -> metal salt + water

Question 27

What products form from reacting a metal hydroxide and acid?

Answer 27

metal hydroxide + acid -> metal salt + water

Question 28

What products form from reacting a metal carbonate and acid?

Answer 28

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

Question 29

On an ionic level, why is an acid and alkali reaction neutralising?

Answer 29

acid + alkali -> water H+ + OH- —> H2O

Question 30

What are electrolytes?

Answer 30

ionic compouns in a solution or liquid (molten) state

Question 31

What is electrolysis

Answer 31

breaking down of an ionic subtance using electrical energy

Question 32

Which electrode has a positive charge?

Answer 32

anode

Question 33

Which electrode has a negative charge?

Answer 33

cathode

Question 34

Where do positively charged cations migrate to during electrolysis?

Answer 34

negatively charged cathode

Question 35

Where do negatively charged anions migrate to during electrolysis?

Answer 35

positively charged anode

Question 36

What occurs at the anode?

Answer 36

oxidation | -loss of electrons

Question 37

What occurs at the cathode?

Answer 37

reduction | -gain of electrons

Question 38

What forms during the electrolysis of copper chloride solution?

Answer 38

anode - oxidation - loss of electrons - chlorine gas cathode - reduction - gain in electrons - copper solid covers electrode

Question 39

What forms during the electrolysis of sodium chloride solution?

Answer 39

anode - oxidation - loss of electrons - chlorine gas forms cathode - reduction - gain in electrons - hydrogen gas forms

Question 40

What forms during the electrolysis of sodium sulfate solution?

Answer 40

anode - oxidation - loss of electrons - oxygen forms cathode - reduction - gain in electrons - hydrogen forms

Question 41

What forms during the electrolysis of water acidified with sulfuric acid? (H2O + H2SO4)

Answer 41

anode - oxidation -> hydroxide - loss of electrons - oxygen forms cathode - reduction - gain of electrons - hydrogen forms

Question 42

What forms during the electrolysis of molten lead bromide?

Answer 42

anode - oxidisation - electron lost - bromine gas - seen as bubbles cathode - reduction - electrons gained - molten lead forms at cathode - silver in colour

Question 43

When is the metal produced at the cathode and when is hydrogen produced instead?

Answer 43

metal produced - if metal is less reactive than hydrogen eg Cu, Ag, Au hydrogen produced - if metal is more reactive than hydrogen

Question 44

What are the half equations for the electrolysis of molten lead bromide?

Answer 44

anode 2Br- —> Br2 + 2e- cathode Pb2+ + 2e- —> Pb

Question 45

What are the half equations for the electrolysis of copper chloride?

Answer 45

anode 2Cl- —> Cl2 + 2e- cathode Cu2+ + 2e- —> Cu

Question 46

What are the half equations for the electrolysis of sodium chloride?

Answer 46

anode 2Cl- —> Cl2 + 2e- cathode 2H+ + 2e- —> H2

Question 47

What are the half equations for the electrolysis of sodium sulfate?

Answer 47

anode 4OH- —> O2 + 2H2O + 4e- cathode 2H+ + 2e- —> H2

Question 48

What are the half equations for the electrolysis of water acidified with sulfuric acid?

Answer 48

anode 4OH+ —> O2 + 2H2O + 4e- cathode 2H+ + 2e- —> H2