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Chemistry GCSE > Chemistry GCSE: C4 Chemical Changes > Flashcards

Chemistry GCSE: C4 Chemical Changes Flashcards

1
Q

What pHs do alkalis have?

Which pH is the most alkali?

A

Alkalis have pHs above (greater than) 7

pH 14 is the most alkali

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2
Q

What pHs do acids have?

Which pH is the most acidic?

A

Acids have pHs below 7

pH 0 is the most acidic

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3
Q

What pH is neutral?

A

pH7

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4
Q

Give two ways that you can measure the pH of a substance.

Say which is better and why?

A

Universal indicator or a pH probe

A probe gives a more precise (and accurate) reading.

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5
Q

What colour does universal indicator go in

Strong acids

Weak acids

A

Strong acids: Red

Weak acids: Orange/yellow

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6
Q

What colour does universal indicator go in

Strong alkalis

Weak alkalis

A

Strong alkalis: Purple

Weak alkalis: Blue

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7
Q

What colour does universal indicator go in

Neutral solutions

A

Neutral solutions: Green

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8
Q

What type of ions do alkalis contain

A

Hydroxide ions (OH-)

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9
Q

What type of ions do acids contain

A

Hydrogen ions (H+)

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10
Q

What is the difference between alkalis and bases?

A

A base: any substance that reacts with acids to form a salt (all alkalis are bases)

Alkalis: Bases that dissolve in water

Some bases e.g iron oxide are not alkalis as they don’t dissolve in water.

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11
Q

What do we call reactions between acids and alkalis/bases?

A

Neutralisation reactions

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12
Q

Why does adding acids and alkalis/bases together lead to neutralisation?

A

Because the hydrogen ions react with the hydroxide ions to make water.

H+ + OH- => H2O

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13
Q

Metal oxides (e.g magnesium oxide) are bases. What two other types of compunds are bases?

A

Metal hydroxides (e.g sodium hydroxide) and metal carbonates (e.g calcium carbonate).

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14
Q

What two things are made when metals react with acids?

Complete this reaction: Sulfuric acid + magnesium =>

A

A salt and hydrogen

Sulfuric acid + magnesium => magnesium sulfate + hydrogen

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15
Q

What two things are made when metal oxides or metal hydroxides react with acids?

Complete this reaction: Hydrochloric acid + iron oxide =>

A

A salt and water

Hydrochloric acid + iron oxide => iron chloride (a salt) + water

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16
Q

What three things are made when metal carbonates react with acids?

Complete this reaction: Nitric acid + calcium carbonate =>

A

A salt, water and carbon dioxide

Nitric acid + calcium carbonate => calcium nitrate + water + carbon dioxide

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17
Q

What types of salts are made using hydrochloric acid?

A

Chlorides (e.g calcium chloride)

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18
Q

What types of salts are made using nitric acid?

A

Nitrates (e.g copper nitrate)

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19
Q

What types of salts are made using sulfuric acid?

A

Sulfates (e.g iron sulfate)

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20
Q

List the steps to make a soluble salt (e.g copper sulfate) from an insoluble base (e.g copper oxide) and an acid (e.g sulfuric acid)

A
  1. Gently warm the acid in a water bath
  2. Add the insoluble base to the acid until no more reacts (it is in excess)
  3. Filter to remove any insoluble base
  4. Heat the solution to evaporate the water
  5. Filter and/or dry the crystals made
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21
Q

Put these metals in order or their reactivity: Potassium, magnesium, lithium, calcium, sodium.

Explain how you worked this out

Click here for the periodic table

A

Potassium, sodium, lithium, calcium, magnesium.

Group 1 elements first (from bottom to top).

Group 2 elements next (from bottom to top)

22
Q

Put the following in order of reactivity:

  • Acid reactions
  • Iron
  • Carbon
  • Zinc
  • Copper
A
  • Carbon (most reactive)
  • Zinc
  • Iron
  • Hydrogen
  • Copper (least reactive)

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23
Q

What two things are made when metals react with water?

Complete the following equation: Magnesium + water =>

A

Metal hydroxides and hydrogen

Magnesium + water => Magnesium hydroxide and hydrogen

24
Q

Which metals don’t react with water?

A

Zinc and metals that are less reactive than zinc (e.g iron, copper, silver)

25
Q

Name two metals that are found as pure metals.

Why are these metals found as pure metals?

A

Gold and silver

Because they are very unreactive.

26
Q

Most metals are not found as pure metals, they are found as metal ores. What type of compounds are metal ores.

A

Metal ores are metal oxides.

27
Q

What two methods can be used to extract metals such as iron from their metal ores/oxides?

A

Displacement using carbon

Electrolysis

28
Q

Why can carbon be used to extract zinc, iron and copper from their ores/oxides?

A

Because carbon is more reactive than zinc, iron, copper and so will displace them from their oxides.

29
Q

Why can’t carbon be used to extract aluminium from its ore/oxide?

A

Because carbon is less reactive than aluminium.

30
Q

Why are zinc, iron and copper extracted using carbon (displacement) instead of using electrolysis?

A

Electrlysis is much more expensive because….

Melting metal ores uses lots of energy

Creating an electric current uses lots of energy

31
Q

Describe oxidation and reduction in terms of oxygen.

A

Oxidation is gain of oxygen

Reduction is loss of oxygen

32
Q

In the following reaction, what has been oxidised and what has been reduced?

zinc oxide + carbon → carbon dioxide and zinc

A

The carbon is oxidised (gains oxygen)

The zinc oxide is reduced (loses oxygen)

33
Q

HIGHER:

Describe oxidation and reduction in terms of electrons (OIL RIG)

A
  • *O**xidation is loss of electrons
  • *R**eduction is gain of electrons
34
Q

In electrolysis, what is the charge of the anode and what is the charge of the cathode?

PANIC

A

Positive Anode

Cathode Is Negtive

35
Q

Whay does electrlysis mean?

What is it used for?

A

Using electricity (electro) to break things up (lysis).

Breaking up ionic compunds into their elements.

36
Q

In what state do ionic compounds have to be for electrolysis.

A

Liquid/molten

or

Aqueous/dissolved/in a solution

37
Q

What does aqueous mean

A

It means that the substance is dissolved in water/in a solution.

38
Q

What charge do non-metal ions have?

In electrolysis, which electrode do the non-metal ions go to?

A

Non-metal ions have a negative charge

They are therefore attracted to the anode (positive electrode)

39
Q

What charge do metal ions have?

In electrolysis, which electrode do the metal ions go to?

A

Metal ions have a positive charge.

So they are attracted to the cathode (negative electrode)

40
Q

In electrolysis, what happen to negative ions when they arrive at the anode (positive electrode)?

A

They lose electrons (oxidised) forming molecules (or atoms).

41
Q

In electrolysis, what happen to positive ions when they arrive at the cathode (negative electrode)?

A

They gain electrons (reduced) forming metal atoms

42
Q

What happens at the anode (positive electrode) during electrolysis of molten aluminium oxide?

A
  • Negative oxide ions
  • Lose electrons (oxidised)
  • Forming oxygen molecules
  • 2O2- → O2 + 2e-
43
Q

What happens at the cathode (negative electrode) during electrolysis of molten aluminium oxide?

A
  • Positive aluminium ions
  • Gain electrons electrons (reduced)
  • Forming aluminium atoms
  • Al3+ + 3e- → Al
44
Q

HIGHER: What happens at the anode (positive electrode) during electrolysis of aqueous copper chloride?

A
  • Negative chloride ions
  • Lose electrons (oxidised)
  • Forming chlorine molecules
  • 2Cl- → Cl2 + 2e-
  • Chlorine is in group 7 so it is the chloride ions not the hydroxide ions from water that lose electrons)
45
Q

HIGHER: What happens at the cathode (negative electrode) during electrolysis of aqueous copper chloride?

A
  • Positve copper ions
  • Gain electrons (reduced)
  • Forming copper atoms
  • Cu2+ + 2e- → Cu
  • Copper is less reactive than hydrogen, so it is the copper ions that gain electrons.
46
Q

HIGHER: What happens at the anode (positive electrode) during electrolysis of aqueous sodium sulfate?

A
  • Negative hydroxide ions
  • Lose electrons (oxidised)
  • Forming water and oxygen molecules
  • 4OH- → 2H2O + O2 + 4e-
  • Sulfate is not in group 7, so it is the hydroxide ions which lose electrons.
47
Q

HIGHER: What happens at the cathode (negative electrode) during electrolysis of aqueous sodium sulfate?

A
  • Positve hydrogen ions
  • Gain electrons (reduced)
  • Forming hydrogen molecules
  • 2H+ + 2e- → H2
  • Sodium is more reactive than hydrogen, so it is the hydrogen ions that gain electrons.
48
Q

Triple:

What is oxidised and what is reduced in the following reaction

Hydrochloric acid + iron → iron chloride + hydrogen

2HCl + Fe → FeCl2 + H2

A
  • The iron atoms are oxidised (lose electrons) forming iron ions
  • Fe → Fe2+ + 2e-
  • The hydrogen ions (from the hydrochloric acid) are reduced (gain electrons) forming hydrogen molecules
  • 2H+ + 2e- → H2
49
Q

Triple:

What is oxidised and what is reduced in the following reaction

Potassium bromide + chlorine → potassium chloride + bromine

2KBr + Cl2 → 2KCl + Br2

2K+ + 2Br- + Cl2→ 2K+ + 2Cl- + Br2

A
  • The bromine ions lose electron (oxidised) forming bromine molecules
  • 2Br- → 2Br + 2e-
  • The Chlorine molecules gain electrons forming chlorine ions
  • Cl2 + 2e- → 2Cl-
50
Q

Triple:

What is oxidised and what is reduced in the following reaction

Iron + copper sulfate → iron sulfate + copper

Fe + CuSO4 → FeSO4 + Cu

Fe + Cu2+ + SO42- → Fe2+ + SO42- + Cu

A
  • The iron atoms lose electrons (oxidised) forming iron ions
  • Fe → Fe2+ + 2e-
  • The copper ions gain electrons (reduced) forming copper atoms
  • Cu2+ + 2e- → Cu
51
Q

Triple:

Describe the steps used in a titration to find the concentration of an acid of unknown concentration.

A
  1. Use a pipette to add a set volume (25cm3) of the acid to a beaker
  2. Add a single indicator (e.g litmus) to the acid)
  3. Fill the burette with an alkali of known concentration
  4. Add the alkali to the acid a few drops at a time
  5. Keep adding the alkali until the acid changes colour
  6. Record the volume of alkali used
  7. Repeat 3-5 times to calculate an average and identify outliers
52
Q

Triple:

What is tritration used for

A

To find the concentration of an acid or alkali of unknown concentration

Chemistry GCSE (10 decks)

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