topic 3 - chemical changes

Question 1

which ph values are alkaline

Answer 1

greater than 7

Question 2

what does the ph scale range from

Answer 2

0-14

Question 3

what terms can be used to describe solutions with a ph of 7

Answer 3

neutral

Question 4

what ph is an acid

Answer 4

0 - 6

Question 5

what ph is an alkaline

Answer 5

8 - 14

Question 6

a substance which forms an aqueous solution with a pH of less than 7 is defined as:

Answer 6

an acid

Question 7

do strong acids ionise completely

Answer 7

yes

Question 8

do weak acids ionise completely

Answer 8

no they ionise partially

Question 9

what does an acids strength mean

Answer 9

how well it ionises (dissociates) when added to water

Question 10

what does an acids concentration mean

Answer 10

how many molecules there are per dm3 of solution

Question 11

what is an electrolyte

Answer 11

a liquid or solution containing an ionic compound- the ions are free to move

Question 12

what do we do if our electrolyte is insoluble

Answer 12

melt it

Question 13

what are electrodes

Answer 13

solid conductors

Question 14

which electrode is positive and which is negative

Answer 14

anode - positive
cathode - negative

Question 15

what is electrolysis

Answer 15

split compounds into their elements

Question 16

which electrode are negative ions attracted to

Answer 16

anode

Question 17

what happens to the charged negative ions when they reach the anode

Answer 17

they are discharged and turned into a neutral ion

Question 18

which electrode are positive ions attracted to

Answer 18

cathode

Question 19

what is happening to ions at the electrodes

Answer 19

they are oxidising and reducing

Question 20

what are the equations that show reduction and oxidation called

Answer 20

half equations

Question 21

in electrolysis which direction do the electrons travel

Answer 21

anode to cathode

Question 22

what is reduction in terms of electrons

Answer 22

reduction is the gain of electrons

Question 23

what is oxidation in terms of electrons

Answer 23

oxidation is the loss of electrons

Question 24

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

Answer 24

so the ions are free to move around

Question 25

which chemical processes are used to extract metals from their ores

Answer 25

electrolysis and reduction with carbon

Question 26

why is electrolysis not used to extract all metals

Answer 26

why is electrolysis not used to extract all metals

Question 27

when should a metal be extracted by carbon reduction

Answer 27

when the metal is less reactive than carbon

Question 28

why is electrolysis used to extract aluminium from its ores

Answer 28

it is more reactive than carbon

Question 29

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

Answer 29

cryolite

Question 30

what colour is phenolphthalein in acid and alkali

Answer 30

acid- colourless alkali- pink

Question 31

what colour is methyl orange in acid and alkali

Answer 31

acid- red alkali- yellow

Question 32

what is a neutralisation reaction

Answer 32

a reaction between an acid and a base

Question 33

what happens during an acid-alkali neutralisation

Answer 33

H+ ions from the acid react with OH- ions from the alkali to form water

Question 34

what is a base

Answer 34

any substance that reacts with an acid to form salt and water only

Question 35

is an alkali a soluble or insoluble base

Answer 35

soluble

Question 36

what are the products when an acid reacts with metal

Answer 36

salt and hydrogen

Question 37

what are the products when an acid reacts with metal oxide

Answer 37

salt and water

Question 38

what are the products when an acid reacts with metal hydroxide

Answer 38

salt and water

Question 39

what are the products when an acid reacts with a metal carbonate

Answer 39

salt and water and carbon dioxide

Question 40

why are metal oxides normally bases rather than alkalis

Answer 40

metal oxides are normally insoluble while alkalis are soluble

Question 41

what is the name of the salt formed from magnesium and sulphuric acid

Answer 41

magnesium sulphate

Question 42

describe the chemical test for hydrogen

Answer 42

squeaky pop test: insert a lit splint into a test tube of gas, a squeaky pop will be heard if hydrogen is present

Question 43

describe the chemical test for carbon dioxide

Answer 43

bubble the gas through limewater, limewater will turn cloudy if co2 is present

Question 44

what method must be used to prepare a salt from an acid and soluble reactant? why?

Answer 44

titration since both of the reactants are soluble, a titration allows you to combine the reactants exactly and avoid an excess of either reactant as this would be hard to remove

Question 45

what 3 steps are required to produce a pure, dry salt from an acid and alkali

Answer 45

- complete a titration to find the volume of acid that reacts exactly with a set volume of alkali - use the titration results to mix the acid and alkali in the correct proportions - evaporate the water from the solution, leaving pure, dry salt crystals

Question 46

how do you carry out a titration

Answer 46

use the pipette and pipette filler to add 25 cm3 of alkali to a clean conical flask add a few drops of indicator and put the conical flask on a white tile fill the burette with acid and note the starting volume slowly add the acid from the burette to the alkali in the conical flask, swirling to mix stop adding the acid when the end-point is reached (the appropriate colour change in the indicator happens). note the final volume reading

Question 47

which chlorides are not soluble

Answer 47

silver chloride and lead chloride

Question 48

are all nitrates soluble

Answer 48

yes

Question 49

are all common sodium, potassium and ammonium salts soluble

Answer 49

yes

Question 50

which 3 common sulphates are insoluble

Answer 50

lead sulphate, calcium sulphate and barium sulphate

Question 51

what is a salt

Answer 51

substance produced by the reaction of an acid with a base

Question 52

which 3 carbonates and hydroxides are soluble

Answer 52

sodium, potassium and ammonium calciums and hydroxides

Question 53

why can an electrolyte carry charge

Answer 53

it is a ionic compound in a molten or aqueous state meaning that the ions are free to move

Question 54

where do charged ions in the electrolyte move to during electrolysis

Answer 54

cations (positive ions) move to the cathode (negative electrode) anions (negative ions) move to the anode (positive electrode)

Question 55

what happens at the anode during elctrolysis

Answer 55

the anions (negatively charged ions) lose electrons to form their elements

Question 56

what happens at the cathode during electrolysis

Answer 56

the cations (positively charged ions) gain electrons to form their elements

Question 57

name the processes that occur at each electrode

Answer 57

anode (positive) - oxidation cathode (negative) - reduction

Question 58

what is formed at each electrode

Answer 58

anode - non-metal cathode- metal or hydrogen

Question 59

how can you predict whether a metal or hydrogen will form at the negative electrode

Answer 59

if hydrogen is above the metal in the reactivity series then the metal will form if metal is more reactive than hydrogen then hydrogen will form

Question 60

what is formed at each electrode during the electrolysis of copper chloride solution

Answer 60

positive electrode- chlorine negative electrode- copper

Question 61

what does oxidation mean in terms of electrons

Answer 61

loss of electrons

Question 62

what does reduction mean in terms of electrons

Answer 62

gain of electrons

Question 63

what are the formulas of common acids

Answer 63

hydrochloric acids- HCl sulphuric acid- H2SO4 nitric acid- HNO3

Question 64

what are the formulas of common alkalis

Answer 64

sodium hydroxide- NaOH calcium hydroxide- Ca(OH)2 lithium hydroxide- LiOH