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GCSE Chemistry > C10 Electrolysis Of Aqueous Solutions > Flashcards

C10 Electrolysis Of Aqueous Solutions Flashcards

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1
Q

Electrolysis first aqueous solutions using carbon electrodes

A

. The cation that is less reactive is reduced
. If the Mattel is higher in the reactivity series you get hydrogen
produced instead of the metals.
. If the metal is below hydrogen in the reactivity series you get the
metal.
. If you have halides (group 7 ions) you get the halogen. With other common negative ions you get oxygen (OH- ions are oxidised and oxygen and water are produced.

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2
Q

During the electrolysis of water:

A

H+ ions are attracted to the cathode, gain electrons and form hydrogen gas
OH- ions are attracted to the anode, lose electrons and form oxygen gas

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3
Q

Ions in water

A

Pure water can conduct electricity because a small proportion of its molecules dissociate into ions. The two ions formed in water are, hydrogen ions, H+, and hydroxide ions, OH-.

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4
Q

Electrolysis of dissolved ionic compounds

A

An electrolyte formed by dissolving an ionic compound contains two pairs of negative and positive ions:
positive hydrogen ions from the water, and positive ions from the compound
negative hydroxide ions from the water, and negative ions from the compound
The ions compete at each electrode to gain or lose electrons.

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5
Q

At the cathode

A

Whether hydrogen or a metal is produced at the cathode depends on the position of the metal in the metal reactivity series:
the metal is produced at the cathode if it is less reactive than hydrogen
hydrogen is produced at the cathode if the metal is more reactive than hydrogen

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6
Q

Electrolysis of copper sulfate solution: aim

A

To investigate the electrolysis of copper sulfate solution using inert (unreactive) electrodes.

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7
Q

Electrolysis of copper sulfate solution: setup

A 
. Copper sulfate solution
. Oxygen gas
. Electrolysis cell
. Carbon electrodes
. Positive  electrode (anode)
. Power supply
. Negative electrode (cathode)
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8
Q

Electrolysis of copper sulfate solution: method

A
  1. Pour some copper sulfate solution into a beaker.
  2. Place two graphite rods into the copper sulfate solution. Attach one electrode to the negative terminal of a dc supply, and the other electrode to the positive terminal.
  3. Completely fill two small test tubes with copper sulfate solution and position a test tube over each electrode as shown in the diagram.
  4. Turn on the power supply and observe what happens at each electrode.
    5.Test any gas produced with a glowing splint and a burning splint.
    Record your observations and the results of your tests.
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9
Q

Electrolysis of copper sulfate solution: results

A

Observations:
Negative electrode: A brown/pink solid forms
Positive electrode: Bubbles of a colourless gas form
Gas test:
Negative electrode:
Positive electrode: The gas relights a glowing splint

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10
Q

Electrolysis of copper sulfate solution: analysis

A

copper metal is formed at the negative electrode

oxygen gas is formed at the positive electrode

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11
Q

Investigation using copper electrodes: aim

A

To investigate the electrolysis of copper sulfate solution using non-inert electrodes.

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12
Q

Copper electrodes take part in the reactions and are described as non-inert:

A

at the positive electrode, copper atoms lose electrons and form copper ions, Cu2+
at the negative electrode, copper ions gain electrons and form copper atoms
This process is used industrially to purify copper.

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13
Q

Investigation using copper electrodes: equipment

A 
. Power supply
. Ammeter
. Copper electrodes
. Copper sulfate solution
. Variable resistor
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14
Q

Investigation using copper electrodes: method

A
  1. Pour some copper sulfate solution into a beaker.
  2. Measure and record the mass of a piece of copper foil. Attach it to the negative terminal of a dc supply, and dip the copper foil into the copper sulfate solution.
  3. Repeat step 2 with another piece of copper foil, but this time attach it to the positive terminal.
  4. Make sure the electrodes do not touch each other, then turn on the power supply. Adjust the power supply to achieve a constant current as directed by your teacher.
  5. After 20 minutes, turn off the dc supply.
  6. Carefully remove one of the electrodes. Gently wash it with distilled water, then dip it into propanone. Lift the electrode out and allow all the liquid to evaporate. Do not wipe the electrodes clean. Measure and record the mass of the electrode.
  7. Repeat step 6 with the other electrode. Make sure you know which is which.
  8. Repeat the experiment with fresh electrodes and different currents.
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15
Q

Investigation using copper electrodes: evaluation

A

The gain in mass by the negative electrode is the same as the loss in mass by the positive electrode. So the copper deposited on the negative electrode must be the same copper ions that are lost from the positive electrode.

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16
Q

Purifying copper by electrolysis

A

Copper is purified by electrolysis. Electricity is passed through solutions containing copper compounds, such as copper sulfate. The anode (positive electrode) is made from impure copper and the cathode (negative electrode) is made from pure copper.

17
Q

Purifying copper by electrolysis

A
  1. A beaker with pure and impure copper rods dipped into copper sulfate solution
  2. The pure copper rod is connected to the negative terminal of a battery and the impure rod is connected to the positive terminal
  3. The pure copper rod has increased in size while the impure rod has deteriorated, leaving a pool of anode sludge at the bottom of the beaker
18
Q

Which electrode gains/losses mass

A

During electrolysis, the anode loses mass as copper dissolves, and the cathode gains mass as copper is deposited.

19
Q

The purification of copper by electrolysis (ions)

A
  1. Four Cu ions are attached to the rod on the right, and four Cu²+ ions are floating in the space between the rods
  2. A battery is connected between the rods and the Cu ions are pulled towards the left rod
  3. There are now four Cu ions attached to the left rod, with four Cu²+ ions floating in the middle

GCSE Chemistry (25 decks)

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