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Chemistry > Chemical Changes > Flashcards

Chemical Changes Flashcards

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1
Q

What is
oxidation/reduction?

A

Oxidation - When a substance gains oxygen
Reducation - When a substance loses oxygen

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2
Q

What is the reactivity series of
metals? What are the trends in
reactivities of metals in reactions
with acids/water?

A

The series shows the metals in order of their reactivity.
Metals above H2
in reactivity series react with acid to produce H2
. The more
reactive the metal is, the quicker and more violent reaction with acid occurs.
Metals below H2
don’t react with acids.
Not all metals above H2
react with water - mostly Group I and II metals. Aluminium
is the borderline case.

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3
Q

What is a displacement
reaction?

A

A reaction where a more reactive metal displaces a less reactive metal from a
compound

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4
Q

How are unreactive metals
found in Earth?

A

In their natural state (well, they are unreactive…)

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5
Q

How can metals less
reactive than carbon be
extracted?

A

Reduction with carbon. Carbon displaces the metal in a metal oxide - gets
oxidised to carbon oxides. Metal from the metal oxide gets reduced to the pure
metal.

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6
Q

How are metals more reactive
than carbon extracted?

A

By electrolysis

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7
Q

How are oxidation and
reduction defined in terms of
electron transfer ?
Higher Tier Only

A

Oxidation – loss of electrons
Reduction – gain of electrons

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8
Q

What is the general equation for a
reaction between metals and
acids? What type of reaction is
this?

A

Metal + acid → salt + hydrogen
Redox reaction, also a displacement reaction

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9
Q

Which metals in the reactivity
series will react with acid?

A

Those above hydrogen

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10
Q

What is the general equation for a
neutralisation reaction?

A

Base + acid → salt + water

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11
Q

What is the general equation for
the reaction between metal
carbonate and acid?

A

Metal carbonate + acid → salt + water + carbon dioxide

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12
Q

What is the general equation for
the reaction between metal oxides
and acids?

A

Metal oxide + acid → a salt + water

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13
Q

What is a redox reaction?

A

A reaction where both oxidation and reduction occurs

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14
Q

Explain in terms of gain or loss of
electrons which species has been
oxidised and which species has been
reduced when magnesium reacts with
hydrochloric acid

A

Magnesium has lost electrons and thus has been oxidised (Mg to Mg2+)
The hydrogen in HCl has gained electrons and thus has been reduced (H+ to H2
)

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15
Q

How is a soluble salt
formed?

A

a) React the excess acid with some insoluble chemical (e.g. metal oxide)
b) Filter off the leftovers
c) Crystallise the product

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16
Q

What do acids and alkalis
produce in aqueous solutions?

A

Acids produce hydrogen ions, alkalis produce hydroxide ions

17
Q

What are bases, acids and
alkalis?

A

Bases are compounds that neutralise acids, acids produce hydrogen ions in
aqueous solutions, alkalis are soluble bases - produce hydroxide ions in aqueous
solutions

18
Q

What is the pH scale and what
does a pH of 7 show?

A

The measure of acidity/alkalinity of a solution; neutral solution

19
Q

State the general equation for a
neutralisation reaction in a short,
ionic form.

A

H+ + OH− → H2O

20
Q

What is a strong acid? What is
a weak acid?
Higher tier only

A

Strong acid is completely ionised in aqueous solution; weak acid is only partially
ionised in aqueous solution

21
Q

What happens to pH as
concentration of H+
increases?

Higher tier only

A

The pH decreases

22
Q

What is a concentrated acid and
what is a dilute acid? Is this the
same as a strong and weak acid?
Higher tier only

A
  • Concentrated acid has more moles of acid per unit volume than dilute (dilute
    refers to solutions of low concentrations)
  • It is not the same - concentration is not the same thing as strength of an acid.
  • Strength refers to whether the acid is completely ionised in water (strong) or
    only partially (weak).
23
Q

As the pH is decreased by one
unit, what change is seen in the
hydrogen ion concentration?
Higher tier only

A

Increases by a factor of 10

24
Q

Name the following salts:
LiNO3
, K2CO3
, MgBr2
, BaSO4

A

Lithium nitrate
Potassium carbonate
Magnesium bromide
Barium sulfate

25
Q

What is electrolysis?

A

The passing of an electric current through ionic substances that are molten or in
solution to break them down into elements; ions are discharged (they lose/gain
electrons) at electrodes to produce these

26
Q

What is an electrolyte?

A

The liquid/solution which conducts electricity

27
Q

What is a cathode and what is
an anode?

A

Cathode is the negative electrode, anode is the positive electrode

28
Q

What occurs at the cathode
and what occurs at the anode
during electrolysis?

A

Reduction occurs at the cathode
Oxidation occurs at the anode

29
Q

In aqueous electrolysis, which
element is discharged at the
cathode? Oxygen is produced at
the anode unless what?

A

The less reactive element discharges at the cathode. Hydrogen is produced unless
there is a less reactive metal, in which case the said metal is produced. Oxygen is
produced at the anode unless the solution contains halide ions, in which case
halogen molecules are produced.

30
Q

How is aluminium manufactured?
Why is it expensive?

A

Aluminium is made through the electrolysis of aluminium oxide and cryolite.
Lots of energy is needed to produce the current in electrolysis which makes this
process expensive.

31
Q

What are the half equations in
the extraction of aluminium?

A

Al3+ + 3 e−
→ Al (cathode)
2 O2− → O2
+ 4 e− (anode)
Oxygen reacts with C of the anode producing CO2
.

32
Q

Why is cryolite used in this
process?

A

It lowers the melting point of aluminium oxide, reducing energy costs

33
Q

What are the half equations in
electrolysis of the aqueous
Na2SO4
? (higher tier only)

A

2 H+
+ 2 e−
→ H2
(cathode)
4 OH−
→ 2 H2O + O2
+ 4 e− (anode)

34
Q

What are the half equations in
electrolysis of the molten and
aqueous KCl?

A

K+ + e−→ K (cathode)
2 Cl−→ Cl2 + 2 e− (anode)

2 H+ + 2 e−→ H2
(cathode)
2 O2− → O2 + 4 e− (anode), respectively

35
Q

What are the half equations in
electrolysis of the aqueous
CuBr2
?

Higher tier only

A

Cu2+ + 2 e−
→ Cu (cathode)
2 Br−
→ Br2
+ 2 e− (anode)

35
Q

What are the half equations in
electrolysis of the aqueous
CuBr2
?

Higher tier only

A

Cu2+ + 2 e−
→ Cu (cathode)
2 Br−
→ Br2
+ 2 e− (anode)

Chemistry (5 decks)

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