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# GCSE: Aqueous Chemistry

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## The rates of aqueous reactions

1. 1 The rate of reaction can be increased by increasing the concentration of the solution. This will mean there are more molecules in the same amount of space, so there will be more collisions.
2. 2 The rate of reaction can be increased by increasing the temperature of the solution. This will give the molecules more energy, making them move faster and collide more. It will also mean they stand a better chance of having the activation energy.
3. 3 The rate of reaction can be increased by increasing the pressure of the solution. This will mean there are more molecules in the same amount of space, so there will be more collisions.
4. 4 Adding a catalyst to the solution will increase the rate of reaction. This is because the catalyst lowers the activation energy needed for the solution to react.
5. 5 The definition for rate of reaction is “change in concentration of product or reactant over time”.

It has the units mol dm-3 s-1

## How to calculate the number of moles in a solution

1. 1 The two most important equations to learn are:

moles = mass / Mr and moles = volume x concentration
2. 2 If you know the moles of one chemical in your balanced equation, you can find out the moles of anything else by looking at the “big number” ratios. For example:

2NaOH + H2SO4 = Na2SO4 + 2H2O

If you had 10 moles of H2SO4, because there is a 2:1 ratio, you would have 20 moles of NaOH.
3. 3 Your volume MUST be converted into dm3 before you use it in your equation. To convert cm3 into dm3 divide your number by 1000.
4. 4 Do not forget to round your answer to a sensible number of significant figures (usually the least amount of significant figures that the question itself goes to).
5. 5 Your Mr can be found by looking at the mass number on the periodic table (this is the bigger of the two numbers- the smaller one is called the proton number

## Top tips for aqueous reactions

1. 1 Anything that is dissolved in an aqueous solution will have the state symbols (aq). For Na+(aq)
2. 2 If your reaction is dissolved in water, then water will have the state symbol (l), for “liquid”.
3. 3 If the question says that your reaction is done under standard conditions, then it means at 1 atmosphere of pressure, at 25'C.
4. 4 When constructing balanced reactions, do not forget to balance your charges when making salts. For example: HCl + Mg = MgCl + 0.5H2 would be wrong. The correct answer would be 2HCl + Mg = MgCl2 + H2.
5. 5 The most important equation reaction to remember is acid + base = salt + water. This crops up all of the time in exams!

• Marked by Teachers essays 36
• Peer Reviewed essays 19
1. ## Investigation into the effect of acid/alkali strength on the heat change when acids and alkalis are mixed

5 star(s)

When the acid and alkali of the same volume are mixed, this will cause the process of neutralisation to occur. Neutralisation is the reaction between an acid and a base. It is the formation of a bond between H+(aq) from the acid and OH-(aq) from the base. These are known as the reacting ions. This is because in the solution the ions are dissociated and thus independent. H+(aq) + OH- (aq) H2O (l) As this is a bond forming process it is known that it will liberate energy, thus all reactions between acids and bases are exothermic.

• Word count: 2282
2. ## The Effect of pH on the Strength of Keratin (hair protein).

4 star(s)

Within each hair strand the keratin chains are also linked with ionic, salt and hydrogen bonding. Hydrogen bonding occurs from the attraction between the electronegative oxygen atoms on the CO groups and the electropositive H atoms on either the OH or NH groups. Although they are individually weaker than disulphide bonds, hydrogen bonds are in much higher proportions to the disulphide bonds making them important in maintaining the tertiary structure of the protein. Hair is very resilient and has elastic properties.

• Word count: 2268
3. ## An investigation into the factors affecting the temperature rise of water heated electrically.

4 star(s)

The longer you leave the heater on the hotter the water will get. I don't want to do number 2 because variable power supplies are not precise enough for the level I want to investigate this to and so therefore the test could be unfair. So I have chosen number 1 because I can use scales with the degree of accuracy of 1/100th cm3. Varying the mass of the water will give me and array of varied results and I can be accurate in my method.

• Word count: 2653
4. ## Investigating The Energy Change During A Neutralisation Reaction.

4 star(s)

I intend to use five different concentrations of hydrochloric acid and they will be: > 1 m > 0.8 m > 0.6 m > 0.4 m > 0.2 m DEPENDANT VARIABLE: The factor I will measure during the experiment, will the temperature change in the solution of the alkali and acid? I will do this by: Measuring the initial temperature of the solution Adding the alkali - sodium hydroxide Measure the temperature after 1 minute preferably after the reaction has taken place.

• Word count: 2119
5. ## To see how the concentration of acid, reacting with potassium carbonate, affects the rate of reaction

4 star(s)

This is because as the reaction starts it is very quick and as the chemicals continue to react the reaction produces less CO2 per 10 seconds so it slows down gradually resulting in a curve, This is because after some time there are fewer acid and potassium carbonate particles so the reaction slows down. I predict that the reaction will go slower when the concentration of the acid decreases. This is because the rate of reaction increases with the concentration.

• Word count: 2989