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GCSE: Aqueous Chemistry
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The rates of aqueous reactions
- 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 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 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 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.
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
The two most important equations to learn are:
moles = mass / Mr and moles = volume x concentration
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 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 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 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 Anything that is dissolved in an aqueous solution will have the state symbols (aq). For Na+(aq)
- 2 If your reaction is dissolved in water, then water will have the state symbol (l), for “liquid”.
- 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 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 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
My aim of this experiment is to find out the concentration of NaOH by titration with standard o.1dm3 Hcl solution.
= 23.9 cm3 to dm3 23.9 ÷ 1000 = 0.0239dm3 First working out the number of moles from the burette Moles = c × vdm3 C = 0.1, v = 0.0239 Moles = 0.1 × 0.0239 = 2.39 ×10-3 Step 2 working out the Concentration of NaOH in the flask C = mole ÷ v dm3 V = 25 cm3 ÷ 1ooo =0.025dm3 C = 2.39 ×10-3 ÷ 0.025 = 0.0956 moledm3 The strongest and weakens of the experiment. During the experiment there are some of the human error that occurred , which include reading the burette wrong or adding the wrong amount of Hcl solution ,this lead us to get a different results .
- Word count: 722
Hydrogen Fuel Cells use two reactants; Hydrogen and Oxygen. These can possibly be sourced from the electrolysis of water, powered by electricity from solar panels, or wind turbines, for a fully emission-free power method. The Hydrogen enters the cell at the anode side of the cell, whereas the oxygen enters at the cathode side of the cell.
- Word count: 465