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GCSE - Chemistry > Topic 3 - Chemical Changes > Flashcards

Topic 3 - Chemical Changes Flashcards

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1
Q

Which ions make aqueous solutions acidic?

A

Hydrogen ions (H⁺)

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2
Q

Which ions make aqueous solutions alkaline?

A

Hydroxide ions (OH⁻)

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3
Q

What is the pH scale?

A

Ranges from 0-14 and measures acidity of alkalinity of a solution

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4
Q

What are the pH ranges for acids and alkalis? What’s the pH of a neutral solution?

A

Acid - less than pH7
Neutral - pH7
Alkali - greater than pH7

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5
Q

What can be used to measure pH?

A

Universal indicator

pH probe

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6
Q

What colour is phenolphthalein in acid and alkali?

A

Acid - colourless

Alkali - pink

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7
Q

What colour is methyl orange in an acid and alkali?

A

Acid - red

Alkali - yellow

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8
Q

What colour is blue litmus paper in an acid and an alkali?

A

Acid - turns red

Alkali - stays blue

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9
Q

What colour is red litmus paper in an acid and alkali?

A

Acid - stays red

Alkali - turns blue

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10
Q

Suggest a problem with using universal indicator to test pH of solution?

A

Colour of solution matched to pH colour chart. Subjective as people can disagree with which colour matches.

Doesn’t provide exact pH value

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11
Q

Acid X has a pH of 1. What can you say about the concentration of hydrogen ions in acid X?

A

High concentration of hydrogen ions - strong acid.

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12
Q

Alkali Y has pH of 8.5. What can you say about the concentration of hydroxide ions in alkali Y?

A

Low concentration of hydroxide ions - weak alkali

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13
Q

If pH decreases by 1 unit, what happens to the concentration of hydrogen ions?

A

The hydrogen ion concentration increases by a factor of 10

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14
Q

What is a neutralisation reaction? What happens during an acid-alkali neutralisation reaction?

A

A reaction between an acid and a base.

H⁺ ions from acid react with OH⁻ ions from alkali to form water.

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15
Q

What’s the ionic equation for a neutralisation reaction?

A

H⁺ (aq) + OH⁻ (aq) -> H ₂O (l)

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16
Q

What do the terms concentrated and dilute mean?

A

Concentrated acids have more molecules of acid per unit volume of water than dilute acids.

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17
Q

What does strength of an acid refer to?

A

Wether the acid will completely dissociate in water or not

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18
Q

An acid only partially dissociates in water, what can be said about the strength of this acid?

A

Weak acid

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19
Q

What is a base?

A

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

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20
Q

True or false? ‘Alkalis are insoluble bases’

A

FALSE

Alkalis are soluble bases

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21
Q

What are the products when an acid reacts with metal?

A

Salt and hydrogen

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22
Q

What are the products when an acid reacts with metal oxide?

A

Salt and water

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23
Q

What are the products when an acid reacts with a metal hydroxide?

A

Salt and water

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24
Q

What are the products when an acid reacts with a metal carbonate?

A

Salt, water and carbon dioxide

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25
Q

Why are metal oxides normally bases rather than alkalis?

A

Metal oxides are normally insoluble

Alkalis are soluble

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26
Q

What is the name of the salt formed from magnesium and sulfuric acid?

A

Magnesium sulfate

27
Q

What is the name of the salt formed from zinc oxide and nitric acid?

A

Zinc nitrate

28
Q

What is the name of the salt formed from calcium carbonate and hydrochloride acid?

A

Calcium chloride

29
Q

Describe the chemical test for hydrogen

A

Insert a lit splint into test tube of gas

A ‘squeaky pop’ will be heard if hydrogen is present

30
Q

Describe the chemical test for carbon dioxide

A

Bubble gas through limewater

Limewater turns cloudy if carbon dioxide is present

31
Q

What is limewater?

A

Calcium hydroxide

32
Q

When a so,bule salt is prepared from an acid and an insoluble reactant, why is excess of the insoluble reactant added?

A

To ensure all the acid reacts

33
Q

When a soluble salt is prepared from an acid and an insoluble reactant, how and why is excess reactant removed?

A

By filtration to leave a pure solution of the salt

34
Q

What method must be used to prepare a salt from an acid and a soluble reactant? Why?

A

Titration
Both reactants are soluble - a titration allows you to combine the reactants exactly and avoid adding excess of either reactant as would be hard to remove.

35
Q

Name the method that could be used to prepare a sample of soluble copper sulfate from insoluble copper oxide and sulfuric acid?

A

Filtration

36
Q

What 3 steps are required when producing a pure dry salt from an acid and alkali?

A

Complete the titration to find the volume of acid that reacts exactly with a set volume of alkali.
Use results to mix acid and alkali in correct proportions
Evaporate water leaving pure dry salt crystals

37
Q

Describe how to carry out an acid-alkali titration.

A

Use pipette - add measured vol of acid to conical flask + add few drops of indicator.
Place on white tile.
Fill burette with alkali, noting initial vol.
Add alkali to flask and find the end point - where indicator first changes colour.
Repeat adding alkali drop by drop and swirling glass constantly to mix.
Récord final vol in burette. Repeat.

38
Q

Most common chlorides are soluble. What are the 2 exceptions?

A

Silver chloride and lead chloride are insoluble

39
Q

True or false? ‘All nitrates are soluble’

A

TRUE

40
Q

Fill in the gap: ‘all common sodium, potassium and ammonium salts are ____’

A

Soluble

41
Q

Most common surfaces are soluble, what are the 3 exceptions?

A

Lead sulfate, calcium sulfate and barium sulfate are insoluble.

42
Q

Most common carbonates and hydroxides are insoluble, what are the 3 exceptions?

A

The carbonate/hydroxides of sodium, potassium and ammonium are soluble.

43
Q

What salt is produced when lead reacts with sulfuric acid? Will a precipitate form?

A

Lead sulfate

A precipitate will form because lead sulfate is insoluble.

44
Q

How could you prep a pure dry sample of an insoluble salt?

A

Mix 2 solutions required
Filter mixture using filter paper
Residue is insoluble salt
Wash with distilled water and leave to dry

45
Q

What is an electrolyte?

A

An ionic compound in its molten or aqueous state.

46
Q

Why can an electrolyte carry charge?

A

An ionic compound in its molten or aqueous state has mobile ions which can carry charge.

47
Q

What is electrolysis?

A

A process which uses electrical energy to decompose electrolytes.

48
Q

What is the cathode and anode?

A

Cathode - negative electrode

Anode - positive electrode

49
Q

What happens at the cathode during electrolysis?

A

Cations (+ ions) gain electrons to form their elements

50
Q

Name the processes that occur at each electrode during electrolysis

A

Anode (+) = oxidation

Cathode (-) = reduction

51
Q

Where do charged ions in the electrolyte move to during electrolysis?

A

Cations (+ ions) move towards the cathode

Anions (- ions) move towards the anode

52
Q

What happens at the anode during electrolysis?

A

Anions (- ions) lose electrons to form their elements

53
Q

What is formed at each electrode in electrolysis?

A

Positive electrode: non metal

Negative electrode: metal or hydrogen

54
Q

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

A

If hydrogen is above the metal in the reactivity series, metal will form.
If metal is more reactive than hydrogen p, hydrogen will form.

55
Q

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

A

+ electrode = chlorine

- electrode = copper

56
Q

What is formed at each electrode during the electrolysis of sodium sulfate solution?

A

+ electrode = oxygen

- electrode = hydrogen

57
Q

What is formed at each electrode during the electrolysis of molten lead bromide?

A

+ electrode = bromine

- electrode = hydrogen

58
Q

Predict what will be formed at each electrode during the electrolysis of molten zinc chloride

A

+ electrode = chlorine

- electrode = zinc

59
Q

What is formed at each electrode during the electrolysis of sodium chloride solution?

A

+ electrode = chlorine

- electrode = hydrogen

60
Q

What is formed at each electrode during the electrolysis of water acidified with sulfuric acid?

A

+ electrode = oxygen

- electrode = hydrogen

61
Q

What are the half equations for the reactions occurring at the cathode and anode during the electrolysis of copper chloride?

A

Anode: 2Cl⁻ -> Cl ₂ + 2e⁻
Cathode: Cu²⁺ + 2e⁻ -> Cu

62
Q

What does oxidation mean in terms of electrons?

A

Loss of electrons

63
Q

What does reduction mean in terms of electrons?

A

Gain of electrons

64
Q

Describe how electrolysis of copper sulfate can be used to purify copper

A

Place 2 copper electrodes in copper sulfate solution. Anode should be impure copper + cathode pure copper. Connect to power supply.

Copper in impure anode pulled towards cathode to form pure copper. Impurities form as sludge below anode. Cu²⁺ ions from copper sulfate remain in solution.

GCSE - Chemistry (8 decks)

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