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Chemistry > Acids & Alkalis > Flashcards

Acids & Alkalis Flashcards

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1
Q

What are acids? (4 marks)

A

They have a pH of 1-6
They turn the universal indicator yellow, orange and red
Can neutralise alkalis
Produces hydrogen ions (H+) in aqueous solutions

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2
Q

Why do you write (aq) next to an acid? (2 marks)

A

Acid are aqueous solutions - which means they are dissolved in water

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3
Q

What is an example of a strong acid? (1 mark)

A

Hydrochloric acid, sulfuric acid

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4
Q

What is an example of a weak acid? (1 mark)

A

Ethanoic acid (vinegar) - CH3COOH, hydrofluoric acid

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5
Q

What are alkalis? (4 marks)

A

Have a pH of 8-14
Turn universal indicator blue or purple
Can neutralise acids
They form negative hydroxide ions (OH-) in aqueous solutions

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6
Q

What are bases?

A

a substance that reacts with an acid to neutralise it and produce a salt
They are usually metal oxides
or metal hydroxides

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7
Q

What is an example of a strong alkali? (1 mark)

A

Sodium hydroxide (NaOH)

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8
Q

What is an example of a weak base? (1 mark)

A

Ammonia (NH3)

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9
Q

What number means neutral on the pH scale?

A

7

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10
Q

What are the methods to measure pH? (2 marks)

A

an indicator or a pH probe

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11
Q

What is an indicator? (1 mark)

A

A substance that changes colour depending on the pH of the solution to which it is added

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12
Q

What happens during the neutralisation reaction of acids and alkalis?

A

the H+ ions react with the OH- ions to produce water
this is the net ionic equation of all acid-base neutralisation
H+ + OH- —> H₂O

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13
Q

What is a universal indicator useful for estimating the pH of?

A

of an unknown solution

operates across a broad range

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14
Q

acid + metal —> …. + …..

A

acid + metal —> salt + hydrogen

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15
Q

acid + metal oxide —> …. + ….

A

acid + metal oxide —> salt + water

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16
Q

acid + metal carbonate —> …. + …. + ….

A

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

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17
Q

acid + alkali —> … + ….

A

acid + alkali —> salt + water

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18
Q

Formula for hydrochloric acid?

A

HCl

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19
Q

Formula for sulfuric acid?

A

H₂SO₄

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20
Q

Formula for nitric acid?

A

HNO₃

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21
Q

Formula for sodium hydroxide?

A

NaOH

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22
Q

Formula for ammonium?

A

NH₄⁺

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23
Q

Formula for nitrate?

A

NO₃−

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24
Q

Formula for sulfate?

A

SO₄²-

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25
Q

Formula for carbonate?

A

CO₃²-

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26
Q

Formula for sulfide?

A

S²-

27
Q

What can ammonium nitrate be used as?

A

a fertaliser

28
Q

What are the steps involved in making a pure, dry sample of a soluble salt?
(To prepare crystals of copper sulfate)

A

To prepare crystals of copper sulfate

  • add copper oxide (one spatula at a time) to sulfuric acid with gentle heating until no more will dissolve/ copper oxide is in excess
  • filter the mixture to remove unreacted copper oxide
  • pour the filtrate into an evaporating basin and heat the solution until crystals just start to appear
  • allow to cool to room temperature and leave to evaporate slowly to obtain blue crystals of copper sulfate
  • ensure to wear eye protection
29
Q

What is the method for titration?

A
  • Put 25cm³ of …. hydroxide (alkali) into a conical flask and add a few drops of indicator
  • Put …. acid into a burette
  • Add the acid slowly to the alkali, with swirling, until the indicator just changes colour
  • Note the amount of acid you added
  • repeat this process until you receive 2 similar results (and calculate an average)
  • Now knowing the amount of acid required to neutralise the alkali, add this amount to 25cm³ of a new sample of alkali, without the indicator
  • You now have salt + water
  • Heat the solution until crystals just start to appear, then leave to cool and evaporate the water slowly to obtain the crystals
30
Q

What is ammonium nitrate made up of (titration)?

A

ammonia + nitric acid

31
Q

What is sodium chloride made up of (titration)?

A

sodium hydroxide + hydrochloric acid

32
Q

Why isn’t potassium added to nitric acid to make potassium nitrate?

A

potassium is very reactive

reaction would be extremely violent

33
Q

Why isn’t copper added to sulfuric acid to make copper sulphate?

A

copper is unreactive

wouldn’t react with acid

34
Q

Why is sulfuric acid stronger than ethanoic acid?

A

Sulfuric acid fully ionises in water
(this results in a larger concentration of H⁺ ions and a very low pH)
ethanoic acid only partially ionises

35
Q

Why is litmus not suitable for titration?

A

It is a wide range indicator and therefore does not give a sharp enough colour change at the endpoint

36
Q

What are titrations?

A

Methods of analysing the concentration of solutions

37
Q

What is a neutralisation reaction?

A

A reaction between an acid and alkali

38
Q

What is a salt?

A

a compound that is formed when the hydrogen atom in an acid is replaced by a metal

39
Q

Formula of phosphate?

A

PO₄³⁻

40
Q

Why do salts have no overall charge?

A

Since the sum of the charges on the ions is equal to zero

41
Q

What is an insoluble substance?

A

a substance (solid) that will not dissolve in a solvent even after mixing

42
Q

What is a solvent?

A

a substance that does the dissolving (e.g. liquid)

43
Q

Why is a carbonate not used in making soluble salts?

A

any carbon dioxide gas produced would have been released into the atmosphere

44
Q

What is the titration equation?

A

concentration = moles / volume in dm³

45
Q

How do you work out the volume in dm³

A

volume (cm) / 1000

46
Q

magnesium + hydrochloric acid reaction?

A

effervescence, temperature increase, pop (splint test)

47
Q

magnesium oxide + hydrochloric acid reaction?

A

effervescence, red (UI)

48
Q

sodium hydroxide + hydrochloric acid reaction?

A

green (UI)

49
Q

potassium carbonate + hydrochloric acid reaction?

A

effervescence, cloudy (limewater)

50
Q

What is corrosion?

A

corrosion occurs when a metal continues to oxidise. The metal may become weaker and eventually, all of it may become metal oxide.

51
Q

Formula for ammonia?

A

NH₃

52
Q

Formula for ethanoic acid?

A

CH₃COOH

53
Q

Why are the types of indicators

A

Methyl orange
Phenolphthalein
Universal indicator
litmus paper

54
Q

Why does potassium carbonate not cause limewater to bubble when heated?

A 
Potassium carbonate (and other group 1 metals apart from lithium carbonate) 
does not decompose to produce carbon dioxide / a gas
55
Q

What evidence is there for a chemical reaction?

A

colour change
formation of a precipitate (solid)
formation of a gas (effervescence)
temperature change

56
Q

Why is it important for the percentage atom economy of a reaction to be as high as possible?

A

Economic reasons

Waste products may be pollutants / greenhouse gases

57
Q

Discuss the difference in pH between a weak acid and strong acid of the same concentration

A

A strong acid completely ionises (dissociates) in aqueous solutions where is weak acids only partially ionise (dissociate). This means the strong acid has a much lower pH than the weak acid. As a result the strong acid has a higher concentration of H+ ions as a greater number of acid molecules ionise (dissociate)

58
Q

What is produced when acids react with metals that are not in group 1?

A

Acids react with metals to produce salts and hydrogen

59
Q

How are solid salts produced from salt solutions?

A

salt solutions can be crystallised to produce solid salts

60
Q

If the pH decreases by one unit, by what factor does the ion concentration increase by?

A

10

61
Q

What is one way to speed up a reaction between a metal oxide and acid?

A

Heat the mixture

62
Q

If the acid was the limiting reactant, how could you tell if all the acid was used up?

A

If only metal oxide remains

63
Q

How could a student obtain a solution from a reaction mixture, when it has finished reacting?

A

Through filtration

64
Q

Describe how salt crystals are produced from salt solution?

A

Crystalise the salt solution - which involves heating the solution until crystals just start to appear and allowing it to cool to obtain crystals - to form salt crystals

Chemistry (8 decks)

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