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Electrochemistry and periodic trends
6 ECAT Chemistry questions with answers and explanations.
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How much charge is needed to deposit 1 mole of copper from Cu2+ ions?
- 1 1 faraday
- 2 2 faradays
- 3 3 faradays
- 4 0.5 faraday
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Correct answer: 2 faradays
Each Cu2+ ion needs two electrons, so one mole needs two moles of electrons, which is 2 faradays.
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In the Daniell cell (Zn and Cu), the anode is:
- 1 Copper
- 2 Zinc
- 3 The salt bridge
- 4 Carbon
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Correct answer: Zinc
Zinc is oxidised, so it is the anode. Copper ions are reduced at the copper cathode.
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Which has the lower first ionisation energy, beryllium or boron?
- 1 Beryllium
- 2 Boron
- 3 They are equal
- 4 Neither has an ionisation energy
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Correct answer: Boron
Boron's outer electron is in a 2p orbital, which is higher in energy and easier to remove than a 2s electron of beryllium.
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Which of these metals reacts most vigorously with water?
- 1 Magnesium
- 2 Lithium
- 3 Potassium
- 4 Calcium
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Correct answer: Potassium
Reactivity increases down Group 1 and potassium is below lithium. It is also more reactive than Group 2 metals in the list.
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What is the oxidation state of chromium in K2Cr2O7?
- 1 +3
- 2 +7
- 3 +2
- 4 +6
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Correct answer: +6
Two K are +2 and seven O are -14. The two Cr must supply +12, so each is +6.
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Which gas is given off when zinc reacts with dilute hydrochloric acid?
- 1 Oxygen
- 2 Hydrogen
- 3 Chlorine
- 4 Carbon dioxide
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Correct answer: Hydrogen
Zinc displaces hydrogen from the acid, giving zinc chloride and hydrogen gas.