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AQA GCSE CHEMISTRY > C5 Chemical Changes > Flashcards

C5 Chemical Changes Flashcards

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1
Q

What is the reactivity series?

A

Caesium Cs+
Francium Fr+
Rubidium Rb+
Potassium K+
Sodium Na+
Lithium Li+
Barium Ba2+
Radium Ra2+
Strontium Sr2+
Calcium Ca2+
Magnesium Mg2+
Beryllium Be2+
Aluminium Al3+
Titanium Ti4+
Manganese Mn2+
Zinc Zn2+
Chromium Cr3+
Iron Fe3+
Cadmium Cd2+
Cobalt Co2+
Nickel Ni2+
Tin Sn2+
Lead Pb2+
Hydrogen H+ (Non-Metal, Reference for Comparison)
Antimony Sb3+
Bismuth Bi3+
Copper Cu2+
Tungsten W3+
Mercury Hg2+
Silver Ag+
Platinum Pt4+
Gold Au3+

carbon is between zinc and aluminium

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2
Q

What does the reactivity series show?

A

The
reactivity series
of metals is a chart showing metals in order of decreasing
reactivity
. In general, the more
reactive
a metal is:

the more vigorous its reactions are
the more easily it loses electrons in reactions to form positive ions (cations)

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3
Q

What is the reaction of a metal with an acid?

A

When a metal reacts with a dilute acid, a salt and hydrogen are formed. For example, magnesium reacts rapidly with dilute hydrochloric acid:

Magnesium + hydrochloric acid → magnesium chloride + hydrogen

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4
Q

What happens when a metal reacts with water?

A

When a metal reacts with water, a metal hydroxide and hydrogen are formed. For example, sodium reacts rapidly with cold water:

Sodium + water → sodium hydroxide + hydrogen

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5
Q

What happens when metals react with oxygen?

A

Many metals react with oxygen to make metal oxides. For example, magnesium burns rapidly in air:

Magnesium + oxygen → magnesium oxide

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6
Q

How do displacement reactions happen in an solution?

A

A more reactive metal can displace a less reactive metal from its compounds
. For example, magnesium is more reactive than copper. It displaces copper from copper sulfate
solution

Magnesium + copper sulfate → magnesium sulfate + copper

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7
Q

What does the pseudonym OIL RIG mean?

A

OIL RIG - oxidation is loss of electrons, and reduction is gain of electrons.

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8
Q

How to extract a metal less reactive than carbon?

A

If a metal is less
reactive than carbon, it can be extracted from its compounds by heating with carbon. Copper is an example of this. Copper mostly occurs as sulfide ores, which are heated in air to convert them to copper(II) oxide. Molten
copper can be produced from copper oxide by heating with carbon:

Copper oxide + carbon → copper + carbon dioxide

2CuO(s) + C(s) → 2Cu(l) + CO2(g)

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9
Q

How to extract metals more reactive than carbon?

A

Electrolysis

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10
Q

Why is gold often found in its native state?

A

Its very low on the reactivity series so it doesn’t often form compounds.

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11
Q

What are acids and what do they form?

A

H+ ions in aqueous solution. For example:

HCl(aq) → H+(aq) + Cl-(aq)

Acidic solutions have
pH
values less than 7.

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12
Q

What are alkalis and what do they form?

A

OH- in aqueous solution. For example:

NaOH(aq) → Na+(aq) + OH-(aq)

Alkaline solutions have pH values greater than 7.

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13
Q

What are bases?

A

A base is any substance that reacts with an acid to form a salt and water only. This means that metal oxides and metal hydroxides are bases.

Bases that are soluble in water are called alkalis and they dissolve in water to form alkaline solutions.

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14
Q

What happens in neutralisation reactions?

A

A neutralisation reaction is a reaction between an acid and a base.
In acid-alkali neutralisation reactions, hydrogen ions from the acid react with hydroxide ions from the alkali:
H+(aq) + OH-(aq) → H2O(l)

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15
Q

What is neutral in pH?

A

pH 7 is neutral and is green with indicator and water is an example of it.

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16
Q

Explain the reaction of magnesium with hydrochloric acid.

A

The reactions of acids with metals are
redox reactions
. For example, the
ionic equation
for the reaction of magnesium with hydrochloric acid is:

2H+(aq) + Mg(s) → Mg2+(aq) + H2(g)

This ionic equation can be split into two
half equations
:

Mg(s) → Mg2+(aq) + 2e-(oxidation)
2H+(aq) + 2e- → H2(g) (reduction)
Notice that:

magnesium atoms lose
electrons
- they are
oxidised
hydrogen ions gain electrons - they are
reduced

17
Q

What is the reaction of acid with a carbonate?

A

A salt, water and carbon dioxide are produced when acids react with carbonates. In general:

Acid + carbonate → salt + water + carbon dioxide

18
Q

What are bases?

A

Metal oxides and hydroxides.

19
Q

What are strong acids?

A

Strong acids completely dissociate into ions in solution. For example, hydrochloric acid is a strong acid. It ionises completely to form hydrogen ions and chloride ions:

HCl(aq) → H+(aq) + Cl-(aq)

Nitric acid and sulfuric acid are also strong acids.

20
Q

What are weak acids?

A

Weak acids only partially dissociate in solution. For example, ethanoic acid is a weak acid. It is only partially ionised to form hydrogen ions and ethanoate ions:

CH3COOH(aq) ⇌ H+(aq) + CH3COO-(aq)

The ⇌ symbol is used in the equation to show that the reaction is a
reversible reaction
and does not go to completion.

21
Q

What does the concentration of the acid mean?

A

The
pH
of a solution is a measure of its concentration of hydrogen ions:

the higher the concentration of H+ ions in an acidic solution, the lower the pH
the lower the concentration of H+ ions in an acidic solution, the higher the pH
This means that, for a given concentration in aqueous solution, the stronger an acid, the lower the pH.

22
Q

How does the concentration affect the pH?

A

If the hydrogen ion concentration in a solution increases by a factor of 10, the pH of the solution decreases by 1 unit.

23
Q

Acid strength is the measure of the ability of the acid to:

A

lose its H+ ions

24
Q

What is the method for making salts?(Required Practical)

A
  1. Add some dilute sulfuric acid to a small beaker.
  2. Add some hot water from a kettle to larger beaker or water bath. Place the beaker of sulfuric acid into the hot water to warm up the acid.
  3. Add a spatula of copper oxide powder to the acid and stir with a glass rod. Continue adding copper oxide powder until it is in
    excess
    .

Filtration
4. Fold a piece of filter paper and put it into a filter funnel. Fit the filter funnel into a conical flask.

  1. Add the reaction mixture from the beaker to the filter paper.
  2. Collect the
    filtrate
    , the copper sulfate
    solution
    . Do not collect the
    residue
    , the unreacted copper oxide.
  3. Pour the filtrate into an evaporating basin.

Crystallisation
8. Set up a Bunsen burner, tripod and gauze on a heat resistant mat.

  1. Put a beaker of water on the gauze and the evaporating basin on the beaker.
  2. Heat the water, adjusting the Bunsen burner flame so the water is just simmering.
  3. Stop heating before all the water in the evaporating basin leaves the copper sulfate solution.
  4. Allow the evaporating basin to cool, then leave it aside for a few days or in a drying oven.
25
Q

Explain why it is possible to have a very dilute solution of a stronger acid with a lower pH than a concentrated solution of a weak acid.

A

pH depends on concentration of H+
(aq) ions
so although weak acid does not ionise completely, it could have a
higher concentration of H+(aq) ions if amount of strong acid per dm3 is
very, very small
Strong acid ionises completely
but in very dilute solution may produce fewer H+
(aq) ions in a given
volume of solution than a concentrated solution of the weak acid

26
Q

Explain why propanoic acid is weaker than nitric acid

A

Any four from:
* propanoic acid does not ionise completely when added to water
* reaction is reversible
* majority of molecules remain intact
* only a small fraction form H+
(aq) ions
* Therefore, propanoic acid does not produce as high a
concentration of H+
(aq) ions as a strong acid of equal
concentration
* Nitric acid is a strong acid, because its molecules ionise
completely in water

27
Q

Compare the advantages and disavantages of using a u.i paper vs a ph sensor

A

any three from:
* pH sensor and data-logger more accurate,
* matching colours against pH chart by eye is subjective and
difficult to judge,
* pH sensor gives more repeatable measurements over narrower
range, giving more precise data
* than U.I. paper,
* also useful for monitoring changes in pH continuously over
time,
* if you only need a rough estimate of pH,
* U.I. paper is quicker and easier to use

28
Q

Explain why the pH of an acid depends on:
* the strength of the acid
* the concentration of the acid.

A

General principle
* pH depends on H+ ion concentration
* the higher the concentration of H+ ions the lower the pH
Strength
* the stronger an acid the greater the ionisation / dissociation (in
aqueous solution)
* (so) the stronger the acid the lower the pH
Concentration
* the higher the concentration of an acid the more acid / solute in
the same volume (of solution)
* (so) the higher the concentration of the acid the lower the pH

29
Q

Describe in detail how you could prepare a sample of copper sulphate crystals from its solutions.

A

Heat copper sulfate solution in evaporating dish on a water bath,
some water evaporates from copper sulfate solution until point of
crystallisation when crystals appear at the edge of the solution,
solution then left at room temperature for the remaining water to
evaporate slowly,
leaving crystals in the dish. If small volume of solution remains on the
crystals dry by gently dabbing between two pieces of filter paper.

30
Q

Write a detailed method to show how to make lithium chloride from an acid and an alkali?

A

add indicator to measured volume of lithium hydroxide solution
add dilute hydrochloric acid until indicator just changes colour noting
volume of acid needed
repeat until results concordant then calculate mean
repeat using this mean volume of acid without indicator
evaporate water from LiCl solution by heating until point of
crystallisation
leave at room temperature for rest of water to evaporate; if necessary,
dry off any remaining solution with filter paper

AQA GCSE CHEMISTRY (15 decks)

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