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Chemistry GCSE > Topic 3- Chemical change (with spec) paper 1 > Flashcards

Topic 3- Chemical change (with spec) paper 1 Flashcards

1
Q

What are acids in solution sources of?

A

hydrogen ions

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2
Q

what are alkalis in solution sources of?

A

hydroxide ions

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3
Q

what pH is a neutral solution?

A

pH 7

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4
Q

what pH are acidic solutions?

A

pH levels lower than 7

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5
Q

what pH are alkali solutions?

A

pH levels higher than 7

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6
Q

What does litmus do with acidic, neutral and alkali solutions?

A

acidic: red
neutral: purple
alkali: blue

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7
Q

What does methyl orange do with acidic, neutral and alkali solutions?

A

acidic: red
neutral: yellow
alkali: yellow

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8
Q

What does phenolphthalein do with acidic, neutral and alkali solutions?

A

acidic: colourless
neutral: colourless
alkali: pink

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9
Q

what is a base?

A

a substance that reacts with an acid to produce a salt and water only

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10
Q

what is an alkali?

A

it is a base that is soluble in water (soluble base)

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11
Q

in an acidic solution the higher the concentration of hydrogen ions the..

A

the lower the pH (closer to 1)

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12
Q

in an alkali solution the higher the concentration of hydroxide ions..

A

the higher the pH (closer to 14)

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13
Q

what is an indicator?

A

a dye that changes colour depending on whether its above or below a certain pH

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14
Q

what happens when the hydrogen ion concentration in a solution increases by a factor of 10?

A

the pH of the solution decreases by 1

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15
Q

what is neutralisation?

A

the reaction between an acid and a base. it produces a salt and water

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16
Q

explain the neutralisation practical to investigate the change in pH on adding calcium oxide (base) to a fixed volume of dilute hydrochloric acid?

A

1) measure out a set volume of hydrochloric acid into a conical flask
2) measure out a fixed mass of calcium oxide and add it to the hydrochloric acid
3) wait for the base to completely react and record the pH of the solution using universal indicator paper.
4) repeat the adding of calcium oxide to the acid until all the acid has reacted. you will see this when you’ve got unreacted calcium oxide sitting at the bottom of the flask
5) plot a graph to see how pH changes with the mass of base added. The graph will go slowly up then straight up then balance off at 7

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17
Q

what happens when you put acid in water?

A

they produce hydrogen ions. all acids can dissociate in solution (splitting up to make the hydrogen ion)

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18
Q

What are strong acids like?

A

they ionise almost completely in water, a large amount of the acid molecules dissociate to release hydrogen ions.

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19
Q

what are weak acids like?

A

they do not fully ionise in solution, only a small amount of the acid molecules dissociate to realise hydrogen ions

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20
Q

what is a dilute substance?

A

an acid with a small amount of acid molecules compared to the volume of water

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21
Q

what is a concentrated solution?

A

an acid with a large number of acid molecules compared to the volume of water

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22
Q

explain the general reactions of acids with metals

A

MASH

metal + acid = salt + hydrogen

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23
Q

explain the general reactions of acids with metal oxides

A

acid + metal oxide = salt + water

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24
Q

explain the general reactions of acids with metal hydroxides

A

acid + metal hydroxide = salt + water

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25
Q

explain the general reactions of acids with metal carbonates

A

acid + metal carbonate = salt + water + carbon dioxide

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26
Q

when is a salt formed?

A

during a neutralisation reaction (a reaction between an acid and a base)

27
Q

what happens to hydrochloric acid, sulfuric acid and nitric acids when they become a salt?

A

hydrochloric acid - chloride salts
sulfuric acid- sulfate salts
nitric acid- nitrate salts

28
Q

What is the chemical test for hydrogen?

A

put a lighted splint into a test tube of hydrogen and it will make a squeaky pop

29
Q

what is the chemical test for carbon dioxide?

A

by putting limewater in the co2 the limewater would go cloudy

30
Q

how could you describe an acid-alkali neutralisation?

A

when hydrogen ions from the acid rear with hydroxide ions from the alkali to form water

31
Q

in terms of solubility what are common salts of sodium, potassium and ammonium?

A

common salts of sodium, potassium and ammonium are all soluble

32
Q

in terms of solubility what are nitrates?

A

soluble

33
Q

in terms of solubility what are common chlorides?

A

soluble (except silver chloride and lead chloride)

34
Q

in terms of solubility what are common sulfates?

A

soluble (except lead, barium and calcium sulfate)

35
Q

in terms of solubility what are common carbonates and hydroxides?

A

insoluble (except for sodium, potassium and ammonium ones)

36
Q

What happens when you make soluble salt from an acid and insoluble base?

A

1) heat the acid in a water bath which speeds up the reaction between the acid and insoluble base (metal oxide/hydroxide)
2) add the base to the acid, they will react to form a soluble salt, you will know when the base is in excess when it sinks to the bottom of the flask
3) filter off the excess solid to get a solution containing the salt and water
4) heat the solution so it evaporates the water and leave to dry to form salt crystals

37
Q

what happens when you make a soluble salt from an acid and a soluble reactant?

A

titration must be used where the acid and alkali are mixed in the correct proportions to neutralise the acid. An indicator will be used to measure the pH. (Use phenolphthalein or methyl orange)
the solution remaining, after reaction, is only salt and water

38
Q

what do you do to make an insoluble salt?

A

use a precipitation reaction

1) dissolve the two salts using deionised water and shake until all of it has dissolved in separate test tubes
2) tip the two solutions into the beaker and stir. the insoluble salt should precipitate out
3) prepare a conical flask with a funnel and filter paper and pour the contents into a beaker
4) rinse the contents of the filter paper with deionised water to make sure all the soluble salt is washed away
5) scrape out the insoluble salt and leave it to dry.

39
Q

explain the practical of making dry hydrated copper sulfate crystals starting from copper oxide including the use of a water bath

A

this is making a soluble salt by reacting an acid and an insoluble base

1) heat the acid in a water bath- this speeds up the reaction between the acid and the insoluble base
2) add the base to the acid which will react to form the soluble salt (and water). you will know when the base is in excess and all the acid has been neutralised as the excess solid will just sink to the bottom of the flask
4) filter off the excess solid to get a solution to get a solution containing only salt and water
5) heat the solution gently to slowly evaporate off some of the water snd leave the solution to cool and allow the salt to crystallise. filter off the solid salt and leave it to dry

40
Q

How do you carry out an acid-alkali titration?

A

1) measure out a set amount of acid into a conical flask using a pipettes and add a few drops of indicator (eg. phenolphthalein)
2) slowly add the alkali to the acid using a burette until you reach the end point- this is when the acid’s been neutralised and the indicator changes colour. Note down this volume.
3) carry out the exact same experiment with the same volumes of acid and alkali but with no indicator, so the salt won’t be contaminated with the indicator
4) when the reaction is complete the solution should only contain salt and water
5) slowly evaporate off some of the water and then leave the solution to crystallise. filter off the solid and dry it- you’ll be left with a pure, dry salt

41
Q

explain the method used to prepare a pure, dry sample of an insoluble salt?

A

you must use a precipitation reaction

1) add 1 spatula of lead nitrate to a test tube and add deionised water to dissolve it, shaking it to make sure it is all dissolved. do the same with the sodium chloride in another test tube.
2) tip the two solutions into a beaker and mix it together. the lead chloride should precipitate out.
3) put a piece of folded filter paper into a filter funnel and put the funnel into a conical flask
4) pour the contents in the funnel and add some more deionised water to make sure you get all the precipitate from the beaker
5) rinse the contents of the filter paper with deionised water to make sure tat tall the sodium nitrate has been washed away
6) scrape the lead chloride onto fresh filter paper and leave it to dry

42
Q

What are electrolytes?

A

they are ionic compounds in the molten state or dissolved in water. They can conduct electricity.

43
Q

what is electrolysis?

A

a process in which electrical energy from a direct current supply decomposes electrolytes

44
Q

what happens in reduction in electrolysis?

A

the positively charged cations migrate to the negatively charged cathode, and are reduced (gain of electrons)

45
Q

what happens in oxidation in electrolysis?

A

negatively charged anions migrate to the positively charged anode, and are oxidised (lose electrons)

46
Q

explain the formation of the products in electrolysis of the electrolyte copper chloride

A

product at cathode: copper
Half equation at cathode: cu 2+ + 2e- = Cu

product at anode: chlorine
Half equation at anode: 2Cl = Cl2 + 2e

47
Q

explain the formation of the products in electrolysis of the electrolyte sodium sulfate

A

product at cathode: hydrogen
Half equation at cathode: 2H+ + 2e- = H2

product at anode: oxygen
Half equation at anode: 4OH- = 2h20 + o2 + 4e-

48
Q

explain the formation of the products in electrolysis of water acidified with sulphuric acid

A

product at cathode: hydrogen
Half equation at cathode: 2H+ + 2e- = H2

product at anode: oxygen
Half equation at anode: 4OH- = 2H2O + O2 + 4e-

49
Q

explain the formation of the products in electrolysis of the electrolyte molten lead bromide?

A

product at cathode: lead
Half equation at cathode: Pb 2+ + 2e- = Pb

product at anode: bromine
Half equation at anode: 2Br- = Br2 + 2e-

50
Q

how do you do half equations?

A

these show how electrons are transferred during reactions. they show what happens at each electrode.

1) put one of things being oxidised or reduced on one side of an arrow, and the thing it gets oxidised or reduced on the other
2) balance up the numbers of atoms just like in a normal equation
3) add electrons on one side to balance up the charge

51
Q

what depends on the method used for electrolysis?

A

if your electrolytes are a solution or if it is a molten ionic substance

52
Q

what is oxidation?

A

loss of electrons, happens at the anode

53
Q

what is reduction?

A

the gain of electrons, happens at the cathode

54
Q

explain the method for electrolysis if your electrolytes a solution

A

1) get two inert electrodes and clan the surface of them using sand paper
2) place both electrodes into a beaker filled with your electrolyte, making sure that you don’t touch the surfaces of the electrodes
3) connect the electrodes to a power supply using crocodile clips and wires. when you turn on the power supply a current will flow through the cell

55
Q

explain the method for electrolysis if your electrolytes a molten ionic substance

A

1) put your solid ionic substance (will become your electrolyte) in a crucible and heat it until its molten (do in fume cupboard)
2) dip two clean, inert electrodes into the electrolyte
3) connect the electrodes to a power supply using clips and wires and the current should flow through the cell

56
Q

explain the electrolysis of molten ionic compounds?

A

a solid ionic can’t be electrolysed because the ions are in a fixed position and can’t move. however molten ionic compounds can be electrolyse because they can move freely

57
Q

what happens at the cathode in the electrolysis of aqueous solutions?

A

if hydrogen ions and metal ions are present , hydrogen gas will be produced if the metal is more reactive than hydrogen. if the metal is less reactive than hydrogen the na solid layer of pure metal will be produced

58
Q

what happens at the anode in the electrolysis of aqueous solutions?

A

if hydroxide or halide ions (chloride, bromide, iodide) are present, molecules of chlorine, bromine or iodine will be formed. if no halide ions are present, oxygen will be formed.

59
Q

investigate the electrolysis of copper sulfate solution with inert electrodes

A

1) place the electrodes in the copper sulfate solution
2) connect the electrodes to a wire and into a power pack
3) copper is less reactive than hydrogen so copper metal is produced at the cathode (you see a coating of carbon on the electrode)
4) because there aren’t any valid ions present, oxygen and water are produced at the anode (you’ll see bubbles of oxygen gas forming)

60
Q

investigate the electrolysis of copper sulfate solution with copper electrodes

A

1) weight the electrodes
2) set up the electrolysis experiment as usual wit the electrodes placed in the solution, whilst connected to a power pack
3) as the reaction continues, the mass of the anode will decrease and the mass of the cathode will increase. this because copper is transferred from the anode to the cathode
4) leave the experiment going for 30 miss to get a decent change in mass
5) after the 30 mins take the electrodes out and dry them and then weigh them to see the change in mass
6) if you increase the current, you will increase the rate of electrolysis so there will be bigger difference in mass.

61
Q

how can the electrolysis of copper sulfate be used to purify copper?

A

1) the impure copper anode is oxidised, dissolving into the electrolyte (copper sulfate) to form copper ions
2) the copper ions are reduced at the pure copper cathode and add to it as a layer of pure copper
3) any impurities from the impure copper anode sink to he bottom of the cell, forming a sludge

62
Q

What determines what goes to the anode and cathode in molten ionic solids through electrolysis?

A

Metal ions are reduced to metal atoms at the cathode

The negative ions are oxidised at the anode to atoms or molecules

63
Q

What determines what goes to the anode and cathode in electrolysis of an aqueous solution?

A

At the cathode hydrogen gas will be produced if the metal is more reactive than hydrogen. If the metal is less reactive than hydrogen then the pure metal will form at the cathode.

At the anode if OH- ions or halide ions are present, molecules of bromine, chlorine or iodine will be formed. If no halide ions are present then oxygen will be formed.

Chemistry GCSE (8 decks)

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