C6 REVISION

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What is electrolysis?
A chemical reaction in which an ionic liquid is decomposed into its elements using an electric current formed from moving ions from both the anode and cathode (electrodes).
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What happens to ions in an ionic substance (solution or molten) and an ionic solid?
Ionic solids are fixed and can't move whereas ions that are molten or in solution are free to move.
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In terms of the Anode and cathode, which are positive and negative?
The Anode is positive and the cathode is negative.
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What is the ionic substance called and what state must it be in to work?
Electrolyte and molten or in solution.
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What happens during electrolysis?
Cations move to the Cathode as they are positive and Anions move to the Anode as they are negative. They discharge here and electrons are removed from the negative ions. They flow around the circuit to the Anode and are passed to the positive ions.
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What is the amount of substance made in electrolysis determined by?
The size of the current and the length of time it flows for.
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How can the quantity of electricity passed in electrolysis be calculated?
Quantity of Electricity = Current x Time
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What happens to Copper (II) Sulfate solution when an electric current is passed through it?
The positive electrode bubbles as oxygen is made and the mass decreases as ions move from it. The negative electrode becomes plated with copper as the ions move to it. The electrolyte will decrease in blueness as it decomposes.
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Why are Hydrogen and Oxygen produced when decomposing aqueous solutions via electrolysis?
Because it is often easier to decompose the water than to decompose the compound.
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What are fuel cells?
Cells in which hydrogen reacts exothermically with oxygen to make an electric current.
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What happens in a fuel cell under alkaline conditions?
The hydrogen is oxidized at the anode. (H2 + 2OH- - 2e- => 2H2O) At the cathode, oxygen gets reduced as it gains electrons. (O2 + 2H2O + 4e- => 4OH-)
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What happens in a fuel cell under acidic conditions?
Each hydrogen atom loses an electron at the anode, to form a hydrogen ion. This is an example of oxidation. then the hydrogen ions move through the electrolyte towards the cathode. The electrons travel around the circuit and the oxygen gets reduced.
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What are the advantages of using a fuel cell?
They produce less pollution, they are very efficient, They transfer energy directly, only have a few stages and are easy to construct. They are also lightweight and compact and have no moving parts.
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What are the disadvantages of using a fuel cell?
They often contain poisonous catalysts which must be carefully disposed of. To make the hydrogen fuel, energy is needed and this energy may come from burning fossil fuels.
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How does rust form?
When iron or steel combines with both oxygen and water.
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What is a redox reaction?
A reaction that involves both oxidation and reduction. (Oxidation being the gain of oxygen and reduction being the removal of oxygen)
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What is an oxidizing agent?
A chemical that removes electrons from another substance.
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What is a reducing agent?
A chemical that gives electrons to another substance.
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Why is rusting a redox reaction?
Because Iron loses electrons (oxidation) and oxygen gains electrons (reduction).
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What are methods of protecting iron or steel from rusting?
Galvanising, Alloying, Tin Plating and Sacrificial Protection.
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What is galvanizing?
Coating iron or steel with zinc that prevents water and oxygen from reaching the iron.
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What is Tin Plating?
Is a barrier between the iron and air and water. If the tin plating is scratched, the iron is likely to corrode and lose electrons.
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What is sacrificial protection?
Placing a more reactive metal in front of the iron or steal, so that will corrode instead. Magnesium or Zinc is usually used.
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What are displacement reactions?
When a more reactive metal will displace a less reactive metal in a reaction. For example, Magnesium will displace zinc.
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Why is displacement a redox reaction?
Because the metal ion is reduced by gaining electrons and the metal is oxidized by losing electrons.
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What are alcohols?
A family of organic compounds containing hydrogen, carbon and oxygen.
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What can ethanol be used for?
To make alcoholic drinks, to make solvents, as fuel for cars.
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How is alcohol made via fermentation?
Yeast is used with glucose solution to form ethanol. Fractional distillation can be later used to extract the pure ethanol from the mixture.
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What are the best conditions for fermentation?
A temperature between 25 degrees and 50 degrees for a few days. There must be an absence of air (oxygen) to prevent the formation of ethanoic acid.
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Describe the process of making ethanol by hydration.
This hydration is a reversible reaction . Ethene can be hyrdrated to make ethanol by passing it over a heated phosphoric acid catalyst.
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What are the benefits and disadvantages of Fermentation?
Benefits = Renewable, Sustainable, higher percentage yield, better for the evironment. Disadvantages = Slower (batch process) not reversible, requires very exact conditions.
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What are the benefits and disadvantages of Hydration?
Benefits = Ethene is available in high quantities due to cracking in oil refineries, is a continuous process, quicker, 100% atom economy. Disadvantages = non-renewable process, must be purified before use, is expensive, not be used to make drinks.
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What is ozone?
A type of oxygen found in the stratosphere.
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Other cards in this set

Card 2

Front

What happens to ions in an ionic substance (solution or molten) and an ionic solid?

Back

Ionic solids are fixed and can't move whereas ions that are molten or in solution are free to move.

Card 3

Front

In terms of the Anode and cathode, which are positive and negative?

Back

Preview of the front of card 3

Card 4

Front

What is the ionic substance called and what state must it be in to work?

Back

Preview of the front of card 4

Card 5

Front

What happens during electrolysis?

Back

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