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Chemistry > Topic 4: Chemical Changes > Flashcards

Topic 4: Chemical Changes Flashcards

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1
Q

What is oxidation/ reduction?

A

Oxidation- when a substance gains oxygen.

Reduction- 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 reaction with acids/water?

A

The series shows the metals in order of their reactivity.

Metals above H2 in the reactive series react with acid to produce H2. The more reactive the metal is, the quicker more violent reaction with acid occurs.

Metals below H2 don’t react with acids.

Not all metals above H2 react with water- mostly group 1 and 2 metals.

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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 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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5
Q

How are metals more reactive than carbon extracted?

A

By electrolysis

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6
Q

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

A

Oxidation- gain of electrons.

Reduction- loss of electrons.

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7
Q

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

A

Metal + Acid—> salt + hydrogen

Redox reaction and a displacement reaction.

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8
Q

Which metals in the reactivity series will react with acid?

A

Those above hydrogen

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9
Q

What is the general equation of the neutralisation reaction?

A

Base + Acid —-> salt + water

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10
Q

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

A

Metal carbonate + acid —-> water + carbon dioxide

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11
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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12
Q

What is a redox reaction?

A

A reaction where both oxidation and reduction take place.

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13
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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14
Q

How is 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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15
Q

What do acids and alkalis produce in aqueous solutions?

A

Acids produce hydrogen ions, alkalis produce hydroxide ions.

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16
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.

17
Q

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

A

The measure of acidity/ alkalinity of a solution.

pH 7- neutral

18
Q

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

A

H+ + OH^- → H20

19
Q

What is a strong acid, what is a weak acid?

A

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

20
Q

What happens to pH as
concentration of H+ increases?

A

The pH decreases.

21
Q

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

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).

22
Q

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

A

Increases by a factor of 10.

23
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.

24
Q

What is an electrolyte?

A

The liquid/solution which conducts electricity.

25
Q

What is a cathode and an anode?

A

Cathode is a negative electrode.

Anode is a positive electrode.

26
Q

What occurs at the cathode and anode during electrolysis?

A

Reduction occurs at the cathode.

Oxidation occurs at the anode.

27
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.

28
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.

29
Q

What are the half equations in the extraction of aluminium?

A

Al^3+ + 3 e- → Al (cathode)

2 O^2- → 02 + 4 e- (anode)

Oxygen reacts with C of the anode producing CO2

30
Q

Why is cryolite used in the manufacturing of aluminium?

A

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

31
Q

What are the half equations in electrolysis of the aqueous Na2SO4?

A

2 H+ + 2 e- → H2 (cathode)

4 OH- → 2H2O + O2 + 4 e-(anode)

32
Q

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

A

K+ + e- → K (cathode)

2 Cl- → Cl2 + 2 e- (anode)

2H+ + 2 e- → H2 (cathode)

2 Cl- → Cl2 + 2 e- (anode), respectively

33
Q

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

A

Cu2+ + 2 e- → Cu (cathode)

2 Br- → Br2 + 2 e- (anode)

Chemistry (3 decks)

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