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Chemistry C2 > 5 Salts and electrolytes > Flashcards

5 Salts and electrolytes Flashcards

1
Q

What are alkalis?

A

soluble hydroxides which are alkaline solutions
produce OH- ions when we add them to water
e.g.sodium hydroxide solution

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2
Q

What are bases?

A

include alkalis, substances which can neutralise acids
metal oxides and metal hydroxides are bases
e.g.iron oxide and copper hydroxide

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3
Q

What pH is pure/distilled water?

A

neutral

pH 7

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4
Q

What are acids?

A

substances which produce H+ ions when we add them to water

e.g. citric (in citrus fruit and fizzy drinks) acid, sulfuric acid, ethanoic (in vinegar) acid

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5
Q

How do we know from the pH scale what is an alkali and what is an acid?

A

less than 7 = acid
7 = neutral
more than 7 = alkali

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6
Q

What is the Bronsted-Lowry theory of acids and alkalis?

A

Acids are normally called ‘something’ acid

Alkalis are normally called ‘something’ oxide

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7
Q

What are indicators?

A

substances which change colour when we add them to acids and alkalis
e.g. litmus paper

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8
Q

What are examples of products on the pH scale?

A

0
1 hydrochloric acid very acidic
2 citric acid (lemon juice)
3 orange juice and vinegar
4
5 black coffee slightly acidic
6 rainwater
7 pure water neutral
8 seawater and baking soda
9 milk of magnesia and soap slightly alkaline
10
11
12 washing soda
13 very alkaline
14 oven cleaner and sodium hydroxide

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9
Q

Explain how neutralisation takes place between acids and alkalis in terms of ions….

A

Acids dissolve in water to form hydrogen ions (H+)
Soluble bases (alkalis) dissolve in water to form hydroxide ions (OH-)
These ions then combine to form water
If there are the same number of these ions each then the solution will become neutral

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10
Q

What does an acid and a metal react together to make?

A

a salt + hydrogen

if the metal is very reactive e.g. sodium or potassium, the reaction with acid is too violent to carry out safely

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11
Q

What does an acid and an insoluble base react together to make?

A

a salt + water

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12
Q

What does the salt formed from a reaction depend on?

A

the metal or base that we use as well as the acid

so bases containing sodium ions will a;ways make sodium salts etc.

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13
Q

In terms of the acid used, what type of salt will be formed from a reaction with hydrochloric, sulfuric, nitric and ethanoic acid?

A 
hydrochloric = chlorides
sulfuric = sulfates
nitric = nitrates
ethanoic = ethanoates
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14
Q

What happens when ammonia reacts with water?

A

forms a weakly alkaline solution

NH3 (aq) + H2O (l) –> NH4+ (aq) + OH- (aq)

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15
Q

What happens when ammonia solution reacts with an acid (e.g.nitric acid)?

A

acid + ammonia solution = an ammonium salt + water

HNO3 (aq) + NH4+ (aq) + OH- (aq) –> NH4NO3 (aq) + H2O (l)

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16
Q

What is the reaction called when we react an acid with an alkali to make a salt and water?

A

a neutralisation reaction

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17
Q

Why do we need to use an indicator?

A

to tell us when the reaction is complete and that the acid and alkali have completely reacted

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18
Q

How do we make insoluble salts?

A

by reacting two soluble salts together

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19
Q

What is the name given to the reaction making an insoluble salt called and why is this?

A

a precipitation reaction

because the salt is formed as a solid

20
Q

Why is the a precipitation reaction important?

A

when we want to remove metal ions from polluted water (the salt formed is a solid making it easier to extract)

21
Q

In a precipitation reaction, what does each reactant contain?

A

one of the ions of the insoluble salt
e.g. LEAD nitrate solution + potassium IODIDE solution –> LEAD IODIDE precipitate + potassium nitrate solution
(Pb2+ + 2I- –> PbI2) key ions separated from spectator ions

22
Q

What is electrolysis?

A

the splitting up of a compound/breaking down of a substance using electricity

23
Q

What must happen for electrolysis to work?

A
  • there must be ions to have a charge to attract to an electrode(not covalent molecules)
  • the ions must be able to move (to the electrode)
  • the electrodes must be inert (unreactive)
24
Q

Why is it hard to predict what will form at the electrodes when we electrolyse a solution?

A

water can also form ions

  • the less reactive element, between hydrogen (H+) ions and the metal will usually be produced at the cathode
  • at the anode, we often get oxygen gas given off from discharged hydroxide ions
25
Q

What happens during electrolysis?

A

positively charged ions move to the negative electrode (cathode) and at the same time the negative ions move to the positive electrode (anode)

26
Q

What is oxidisation?

A

a loss of electrons
at the anode the ions give away electrons
impure copper dissolves
e.g. Cu(s) –> Cu2+(aq) + 2e-

27
Q

What is reduction?

A

a gain of electrons
at the cathode the ions pick up electrons
pure copper is plated
e.g. Cu2+(aq) +2e- –> Cu(s)

28
Q

What are the uses of electrolysis?

A
  • to make pure metal

- to split up elements e.g. aluminium oxide, lead bromide

29
Q

What is important about the electrolysis of sodium chloride solution, brine?

A 
Produces 3 very useful products:
Sodium chloride(aq) -->(electrolysis) hydrogen(g) + chlorine(g) + sodium hydroxide(aq)
30
Q

What are the half equations in the electrolysis of brine?

A

at the cathode:
2H+ + 2e- –> H2 (hydrogen ions are less reactive than sodium ions)
at the anode:
2Cl- –> Cl2 + 2e-

31
Q

What are the uses of hydrogen?

A
  • pure so is useful in the food industry to manufacture margarine by reacting hydrogen with vegetable oils
  • can also be used to make hydrochloric acid…
32
Q

What are the uses of chlorine?

A
  • used in water and sewage treatment
  • used in the manufacture of: PVC, textiles, solvents, titanium dioxide, pesticides
  • used in drugs to treat leukaemia, heart disease and arthritis
  • can also be used to make hydrochloric acid and bleach…
33
Q

What are the uses of sodium hydroxide?

A
  • used for purifying petroleum and natural gas
  • used for degreasing metals
  • used in water and sewage treatment
  • used in the manufacture of: paper, cellulose, wrapping, artificial fibres, soaps, detergents, aluminium and titanium dioxide
  • can also be used to make bleach…
34
Q

What are the uses of hydrochloric acid?

A
  • used in cleaning materials
  • used for water and efficient treatment
  • used in the manufacture of: medicine, food products (e.g. soy sauce, gelatin), cosmetics, synthetic rubber, precious metals (e.g. gold)
35
Q

What are the uses of bleach?

A
  • used for treating water in swimming pools

- used for household bleach

36
Q

What are the 3 useful products made from the electrolysis of brine?

A
  • chlorine) used to make bleach which kills bacteria and to make plastics
  • hydrogen) used to make margarine
  • sodium hydroxide) used to make bleach, paper and soap
37
Q

What are the uses of aluminium?

A
  • pans
  • overhead power cables
  • aeroplanes
  • cooking foil
  • drink cans
  • window and patio door frames
  • bicycle frames and car bodies
38
Q

What makes aluminium useful?

A
  • low density
  • very strong
  • oxidised layer prevents it from rusting so does not corrode
  • shiny so it reflects heat
39
Q

How is aluminium extracted?

A

electrolysis

40
Q

What is bauxite ore?

A

ore mined by open cast mining containing mainly aluminium oxide with a few other rocky impurities such as iron oxide

41
Q

How is aluminium produced?

A
  • aluminium oxide is dissolved in molten cryolite in order to use less energy to melt it (from 2000 degrees C to 850 degrees C)
  • during electrolysis, the aluminium metal is collected at the negative electrode in the cells whilst oxygen is formed at the positive electrode
42
Q

During the electrolysis of aluminium oxide, why do the carbon anodes need regular replacement?

A

because they burn away as they react with oxygen to form carbon dioxide

43
Q

What is electroplating?

A

when an object is coated with a thin layer of metal by electrolysis (an electroplated object)

44
Q

Why do we electroplate objects?

A
  • to protect the metal beneath from corroding
  • to make the object look more attractive
  • to increase the hardness of the surface and its resistance to scratching
  • to save money by using a thin layer of precious metal instead of the pure expensive metal (also helps people who are allergic to metals such as nickel used in cheap jewellery)
45
Q

How does electroplating work?

A
  • the positive electrode (anode) is made from the plating metal (they are oxidised and lose electron(s) to form ions which go into the solution)
  • the metal to be plated is used as the negative electrode (cathode) (the plating ions from the solution are reduced, gaining electron(s) to form atoms deposited on the cathode)
  • the electrolysis takes place in a solution (electrolyte) containing ions of the plating metal

Chemistry C2 (5 decks)

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