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Chemistry IGCSE CIE Extended > 8. Acids, Bases & Salts > Flashcards

8. Acids, Bases & Salts Flashcards

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1
Q

What pH value do acids have?

A

Acids have pH values of below 7

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2
Q

What property do acids have which makes them dangerous?

A

They’re corrosive

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3
Q

What colour does blue litmus paper turn in acidic conditions?

A

Blue litmus paper turns red

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4
Q

What colour does methyl orange indicator turn in acidic conditions?

A

methyl orange indicator turns red

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5
Q

What can acids do to bases?

A

Acids are substances that can neutralise a base, forming a salt and water

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6
Q

When acids react, what will they form? (in terms of ions)

A

When acids react, they will lose electrons to form positively charged hydrogen ions (H+)

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7
Q

What makes a solution acidic?

A

The presence of H+ ions is what makes a solution acidic

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8
Q

What metals react with dilute acids?

A

Only metals above hydrogen in the reactivity series will react with dilute acids.

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9
Q

What is formed when metals react with acid?

A

When acids react with metals they form a salt and hydrogen gas:
Acid + Metal → Salt + Hydrogen

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10
Q

What type of oxides are metal oxides and metal hydroxides?

A

Metal oxides and metal hydroxides can act as bases

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11
Q

What happens when metal oxides/hydroxides react with acid?

A

When they react with acid, a neutralisation reaction occurs

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12
Q

What is produced by a neutralisation reaction?

A

In all acid-base neutralisation reactions, salt and water are produced
Acid + Base → Salt + Water

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13
Q

What happens when an acid reacts with a metal carbonate? products?

A

Acids will react with metal carbonates to form the corresponding metal salt, carbon dioxide and water:
Acid + Metal Carbonate → Salt + Carbon Dioxide + Water

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14
Q

What pH do bases have?

A

Bases have pH values of above 7

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15
Q

What is an alkali?

A

A base which is water-soluble is referred to as an alkali

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16
Q

What colour does red litmus paper turn in alkaline conditions?

A

In basic (alkaline) conditions red litmus paper turns blue

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17
Q

What colour does methyl orange indicator turn in alkaline conditions?

A

methyl orange indicator turns yellow

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18
Q

In what ways can bases react with acids?

A

Bases are substances which can neutralise an acid, forming a salt and water

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19
Q

In what forms do bases usually appear?

A

Bases are usually oxides or hydroxides of metals

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20
Q

What happens to alkalis when they react? (in terms of ions)

A

When alkalis react, they gain electrons to form negative hydroxide ions (OH–)

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21
Q

What makes a solution alkaline

A

The presence of the OH– ions is what makes the aqueous solution an alkali

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22
Q

What happens to ammonium salts when warmed with an alkali?

A

Ammonium salts undergo decomposition when warmed with an alkali

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23
Q

What makes ammonia dangerous? How can this problem be fixed?

A

Even though ammonia is itself a weak base, it is very volatile and can easily be displaced from the salt by another alkali

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24
Q

What is produced in the reaction between alkalis and ammonium salts?

Give an example equation between ammonium chloride and sodium hydroxide

A

A salt, water and ammonia are produced
Example:

NH4Cl + NaOH →NaCl + H2O + NH3

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25
Q
  1. What is the reaction between ammonium chloride and sodium hydroxide used for?
A

This reaction is used as a chemical test to confirm the presence of the ammonium ion (NH4+)

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26
Q
  1. How does the test for ammonia work?
A

Alkali is added to the substance with gentle warming followed by the test for ammonia gas using damp red litmus paper

The litmus paper will turn from red to blue if ammonia is present

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27
Q

What is the pH scale?

A

The pH scale is a numerical scale which is used to show how acidic or alkaline a solution is

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28
Q

From what scale does the pH scale range?

A

0-14

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29
Q

What does it mean if the pH value of an acid is very low?

A

The lower the pH then the more acidic the solution is

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30
Q

What does it mean if the pH value of an alkali is very high?

A

The higher the pH then the more alkaline the solution is

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31
Q

What does it mean if a substance has a pH of 7?

A

A solution of pH 7 is describe as being neutral e.g. water

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32
Q

What type of indicator can be used to measure pH?

A

Universal indicator is a mixture of different indicators which is used to measure the pH

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33
Q

How is universal indicator used?

A

A drop is added to the solution and the colour is matched with a colour chart which indicates the pH which matches specific colours

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34
Q

Why is soil pH analysed?

A

Soil pH is analysed to indicate the acidity or alkalinity of soil

35
Q

What PH’s do most plants favour?

A

Most plants favour a pH value of between 5 and 8

36
Q

What happens if the soil pH is not ideal for the plant?

A

Changes in soil which cause a pH to be outside this range adversely affect plant processes resulting in reduced growth and crop yield

37
Q

How may soils become acidic?

A

Soils may become acid from acid rain, overuse of fertilisers which contain ammonium salts or by the excessive breakdown of organic matter by bacteria

38
Q

How can soil be neutralised?

A

Crushed or powdered limestone (calcium carbonate) or lime (calcium oxide) or slaked lime (calcium hydroxide) is added to neutralise the excess acidity in the soil

39
Q

Why must the process in which soil is neutralised be monitored?

A

The addition process must be carefully monitored though, as if added in excess, further damage could be done if the pH goes too high

40
Q

What are acids? (in terms of protons) Why?

A

Acids are proton donors as they ionize in solution producing protons, H+ ions

41
Q

What are alkalis? (in terms of protons) Why?

A

Bases (alkalis) are proton acceptors as they ionize in solution producing OH– ions which can accept protons

42
Q

What determines whether an acid or base is strong or weak?

A

Acids and alkalis can be either strong or weak, depending on how many ions they produce when dissolved in water

43
Q

What determines a strong acid or alkali?

A

Strong acids and bases ionize completely in water, producing solutions of very low pH for an acid or very high pH for a base

44
Q

What are examples of strong acids and bases?

A

Strong acids include HCl and H2SO4 and strong bases include the Group I hydroxides

45
Q

What determines a weak acid or base?

A

Weak acids and bases partially ionize in water and produce pH values which are closer to the middle of the pH scale

46
Q

What are examples of weak acids?

A

Weak acids include organic acids such as ethanoic acid, CH3COOH

47
Q

What are examples of weak bases?

A

weak bases include aqueous ammonia

48
Q

What is usually set-up for both weak acids and bases once they’re added to water?

A

For both weak acids and bases, there is usually an equilibrium set-up between the molecules and their ions once they have been added to water

49
Q

Give an example for the ions forming aqueous ammonia

A

NH3 + H2O ⇌ NH4+ + OH-

50
Q

In the example for aqueous ammonia and its ions, to which direction does the equilibrium lie and why?

A

In both cases the equilibrium lies to the left, indicating a high concentration of intact acid / base molecules, with a low concentration of ions in solution

51
Q

What determines if a solution of an acid or base is concentrated?

A

A concentrated solution of either an acid or a base is one that contains a high number of acid or base molecules per dm3 of solution

52
Q

Is a concentrated acid strong?

A

NO
It does not necessarily mean that the acid or base is strong though, as it may be made from a weak acid or base which does not dissociate completely

53
Q

Do acidic and basic oxides have the same properties?

A

NO

Acidic and basic oxides have different properties and values of pH

54
Q

What determines the pH of an oxide?

A

The difference in their pH stems from whether they are bonded to a metal or a nonmetal element

55
Q

What does the metallic character influence? (oxides)

A

The metallic character of the element influences the acidic or alkaline behaviour of the molecule

56
Q

When are acidic oxides formed?

A

Acidic oxides are formed when a nonmetal element combines with oxygen

57
Q

What happens when an acidic oxide is dissolved in water?

A

When dissolved in water they produce an acidic solution with a low pH

58
Q

What happens when an acidic oxide reacts with a base?

A

They react with bases to form a salt and water

59
Q

What are common examples of acidic oxides?

A

Common examples include SO2 and SiO2

60
Q

When are basic oxides formed?

A

Basic oxides are formed when a metal element combines with oxygen

61
Q

What happens when a basic oxide is dissolved in water?

A

When dissolved in water they produce a basic solution with a high pH

62
Q

What happens when a basic oxide reacts with an acid?

A

They react with acids to form a salt and water

63
Q

What are common examples of basic oxides?

A

Common examples include NaOH, KOH and Ca(OH)2

64
Q

What are neutral oxides?

A

Some oxides do not react with either acids or bases and thus are said to be neutral

65
Q

What are examples of neutral oxides?

A

Examples include N2O, NO and CO

66
Q

What are amphoteric oxides?

A

Amphoteric oxides are a curious group of oxides that can behave as both acidic and basic, depending on whether the other reactant is an acid or a base

67
Q

What is formed when an amphoteric oxide reacts with an acid or a base?

A

In both cases a salt and water is formed

68
Q

What are examples of amphoteric oxides?

A

Two most common amphoteric oxides are zinc oxide and aluminum oxide

69
Q

Do the hydroxides of zinc and aluminium also react amphoterically?

A

YES

70
Q

What is a salt?

A

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

71
Q

How can salts be used?

A

These uses include fertilisers, batteries, cleaning products, healthcare products and fungicides

72
Q

How many parts does the name of a salt have?

A

The name of a salt has two parts

73
Q

Where does the first part of a salt name come from?

A

The first part comes from the metal, metal oxide or metal carbonate used in the reaction

74
Q

Where does the second part of the salt name come from?

A

The second part comes from the acid

75
Q

how can the name of. asalt be determined?

A

The name of the salt can be determined by looking at the reactants

76
Q

What are two key things to consider when preparing salts?

A
  • Is the salt being formed soluble or insoluble in water?

- Is there water of crystallisation present in the salt crystals?

77
Q

Are sodium, potassium and ammonium salts soluble?

A

Yes, all of them are

78
Q

Are nitrates soluble?

A

Yes, all of them are

79
Q

Are ethanoates soluble?

A

Yes, all of them are

80
Q

Are chlorides soluble?

A

Most of them,
Exceptions include:
Silver and Lead(II)

81
Q

Are sulfates soluble?

A

Most of them,
Exceptions include:
Barium, Calcium and Lead (II)

82
Q

Are carbonates soluble?

A

Most of them are INSOLUBLE,
Exceptions include:
Sodium, potassium and ammonium

83
Q

Are hydroxides soluble?

A

Most of them are INSOLUBLE,
Exceptions include:
Sodium, potassium and calcium (calcium hydroxide is slightly soluble)

84
Q

8.2.1 look at methods of salt preparation

A

:)

Chemistry IGCSE CIE Extended (15 decks)

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