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IGCSE Chemistry > C5 - Electricity and chemistry > Flashcards

C5 - Electricity and chemistry Flashcards

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1
Q

PANIC

A

Positive is Anode, Negative Is Cathode

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2
Q

What is electrolysis

A

the process of splitting an ionic compound when molten or aqueous solution by the passage of electricity

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3
Q

When ionic compounds are melted or dissolved in water the ions are

A

free to move around in the solution

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4
Q

What is an electrode

A

rod that conducts electricity (they come in pairs of Pos and neg)

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5
Q

What is a electrolyte

A

ionic compounds dissolved in water to make a solution that conducts electricity

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6
Q

How do we distinguish a difference between electrolytes and non-electrolytes

A

By using a complete circuit which shows whether a light bulb will glow or not.

Electrolytes will make the light bulb glow
Non-electrolytes will do nothing

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7
Q

When a voltage (d.c) is applied across an electrolyte where do the charged ions go

A

Oppositely attract
Positive ions go to negative electrode (cathode)
Negative ions go to positive electrode (anode)

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8
Q

When an ion touches an electrode electrons can be

A

transferred to form elements.

E.g if Cu2+ ions in a solution move to the cathode due to voltage applied, when they touch the cathode each Cu2+ will gain 2 electrons and form a copper metal

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9
Q

How can ionic compounds under go electrolysis

A

When ionic compounds are dissolved in a solution or turned molten the ions are free to move.

The solution can then conduct electricity and will attract to a certain electrode.

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10
Q

If copper ions (Cu2+) are in a solution and a voltage is applied, which electrode will they move towards and what will happen when they touch that electrode?

A

When a voltage is applied across an electrolyte, the charged ions are attracted to the oppositely charged electrodes.

Copper ions (Cu2+) are positively charged, so will move towards the cathode (negative electrode).

When the copper ions (Cu2+) touch the cathode, each ion will gain 2 electrons, forming copper metal:
Cu2+(aq) + 2e- → Cu(s)

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11
Q

What substance are electrodes made out of and why

A

Usually made out of carbon or platinum as they are inert meaning they won’t undergo the chemical change during electrolysis.

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12
Q

Describe what happens during the electrolysis of molten lead bromide

A

When PbBr2 is melted the ions are free to move.

The voltage is applied and the positive lead ions move to the cathode
The negative bromide ions move to the anode
The products of the electrolysis are the elements bromine and lead as the ions gain or loss their electrons to form elements.

Silvery deposits of lead form near the cathode and brown bromine vapor form near the anode to show electrolysis occurred.

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13
Q

What are the half equations of electrolysis of molten lead bromide

A

Pb2+ + 2e- ==> Pb

2Br- ==> Br2 + 2e-

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14
Q

Electrolysis of Aqueous solutions

A

Water molecules in the solution split up to form H+ ions and OH- ions.

What is formed at the cathode:
If the metal is more reactive than hydrogen, hydrogen is produced.
If the metal is less reactive than hydrogen, the metal is produced.

What is formed at the anode:
If halide ions are present, the halogens form
If halide ions are absent, oxygen forms

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15
Q

Electrolysis of sodium chloride solution NaCl

A

Ionic compound NaCl dissolves in water.
Sodium and chloride ions separate and are free to move.
Hydrogen and hydroxide ions also are free to move separated from the water.

Sodium is more reactive than hydrogen so, hydrogen ions are discharged and form as molecules at the cathode. The sodium ions stay in the solution

Since there is a presence of a halide ion (chloride), chlorine ions discharge and form chlorine molecules at the anode. OH- ions stay in the solution

BaCl ==> Na+ + Cl-
H2O <==> H+ + OH-

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16
Q

What is dissociation

A

the process in which water breaks up and forms ions

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17
Q

In NaCl solution what determines whether the anode produces chlorine or oxygen atoms

A

When NaCl solution is dilute OH- ions form at the anode to produce oxygen

When NaCl solution is concentrated Cl- ions form at the anode to produce chlorine

18
Q

If magnesium chloride solution is electrolyzed what substance will form at the cathode

A

Hydrogen will form at cathode as it is less reactive than magnesium

19
Q

Observation of the electrolysis of copper sulfate solution with carbon electrodes

A

copper and oxygen are produced.

Copper forms as a reddish brown coating on the cathode
Oxygen forms as colorless gas bubbles on the anode

The solution becomes paler blue as copper ions are discharged

20
Q

What happens of the electrolysis of copper sulfate solution with copper electrodes

A

Cu2+ ions gain two electrons and are discharged at the cathode. Copper atoms are formed and the mass of the electrode increases

At the node copper atoms lose two electrons and Cu2+ ions are formed.
The anode dissolves and loses mass

21
Q

Why does the concentration of Cu2+ ions in the electrolysis of copper sulfate solution stay the same

A

because rate of production of cu2+ ions at the anode is exactly balanced by the rate of removal of Cu2+ ions at the cathode. It is an important reaction in refining copper

22
Q

How is copper ore refined

A

Copper is extracted from its ore by reduction with carbon but the copper produced is not pure enough for its uses like electrical cables.

It can be purified using electrolysis with copper electrodes

23
Q

Electroplating involves using

A

electrolysis to coat an object with a thin film of metal

24
Q

Electroplating is

A

a good way of improving appearance of metals and preventing their corrosion

25
Q

How does electroplating work

A

Placing the metal to be electroplated at the negative electrode (cathode) and coating the metal at the positive electrode (anode)

26
Q

We use copper, steel and aluminum for electroplating

A

We use them for things like electric cables as they are metals that are good at conducting electricity.

27
Q

Why do we use electroplating

A

to coat cheaper metals with more expensive metals

28
Q

Aluminum is extracted from the ore

A

bauxite

29
Q

Aluminum oxide is extracted from bauxite by

A

purification

30
Q

What are the conditions of extracting aluminum

A

First we have to purify the aluminum oxide from bauxite

Since aluminum is insoluble in water and has extremely. high MP. We dissolve it in molten cryolite at 950 C to make it easier and more energy efficient.

It allows ions to move when an electric current is passed through

31
Q

How do we test for oxygen and hydrogen produced via electrolysis

A

squeaky pop test - hydrogen
relit splint - oxygen

Litmus paper test
Blue - oxygen as it is alkaline
Red - hydrogen as it is acidic

32
Q

In extracting aluminum what forms at the cathode and anode

A

Overall equation:
2Al2O3 ==> 4Al + 3O2

C + O2 ==> CO2

Cathode: Aluminum
Al3+ + 3e- ==> Al

Anode: oxygen
2O2 ==> O2 + 4e-

33
Q

Why do the rods need to be constantly replaced in the extraction of aluminum

A

because oxygen reacts with the carbon anodes to form CO2 which escapes.

34
Q

Why is the extraction of aluminum not common

A

because it is costly and requires loads of energy and electricity.

35
Q

When do we decide whether to make a ionic compound molten or dissolved in water during electrolysis

A

When an ionic compound is insoluble like most metal oxides we turn them into liquid with heat.

Soluble ionic compounds can just be dissolved in water

36
Q

Why we can’t do electrolysis of solid aluminum oxide

A

as the ions are fixed in place and electrolysis only occurs with free flowing ions

37
Q

What process manufactures sodium hydroxide, hydrogen and chlorine

A

electrolysis of concentrated sodium chloride solution (brine)

38
Q

What type of cell is used for the electrolysis of concentrated sodium chloride

A

membrane cell

39
Q

Uses of sodium hydroxide

A

Bleach
Paper
Soap

40
Q

Uses of chlorine

A

Sterilizing drinking water
Bleach
Hydrochloric acid

IGCSE Chemistry (16 decks)

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