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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!

1. ## Testing Acids To Use For De-Scaling Coffee Machines

This means that it needs to be dissolved in a liquid before it can be used. It also works better if you use boiling water as there is more energy to be used for the reaction. However, it is still not as effective sulfamic acid Advantages of sulfamic acid: This acid is the fastest de-scaler. It separates into hydroxonium ions more readily in watery liquids than the other acids. Therefore there are more atoms to react with the calcium in limescale. This acid does not produce any harmful and toxic gases such as chlorine. Disadvantages of sulfamic acid: Sulfamic acid is very irritating to some people?s eyes and skin and is also the most expensive.

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2. ## Plan to investigate the factors that affect the rate of reaction between sodium thiosulfate and hydrochloric acid

This increases the rate of reaction, as there are more successful collisions per second while a lower temperature would decrease the rate of reaction. Changing the concentration of the reactants - This would affect the results of the experiment because the concentration is a measure of the number of particles per unit volume. As the concentration of a solution increases, there are more reactant particles in the same volume and this increases the chances of particles colliding with each other.

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3. ## Separation Of A Mixture of Salt, Sand and Iron Filings

Some metals are magnetic, meaning that they can be turned into or attracted to magnets. This quality means that a magnet can be used to separate substances such as iron that are separatable from non-magnetic substances. However, other materials can be dissolved in water, to form a solution. Another method of separating mixtures is through evaporation. This method is often used to extract an un-dissolved material (such as salt) from a mixture containing water. In this case, if a mixture containing sand and water were left at room temperature, the water would evaporate, leaving only the sand at the bottom.

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4. ## Decomposing Malachite. Purpose: To test the assumption that a chemical reaction is stoichiometric.

oxide once Malachite has decomposed. Controlled: Temperature Malachite is heated to Time Heated (Until Malachite completely decomposes) Method: Note: For safety reasons, wear a protective mask while experimenting with the decomposed copper (II) oxide as it is toxic when inhaled. 1. A varying amount of malachite is added to a dish 2. The malachite is stirred until it becomes a powder with an even composition. 3. While continuing to stir, heat the malachite on a hot plate to 200 degrees Celsius. Continue heating until the green malachite fully decomposes (indicated by the completely black colour of copper (II)

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5. ## How does temperature affect the dissolving rate of a sugar cube?

We tested this by filling a beaker with different temeperature's ranging from 0 degrees celecius to 100. We recorded the time range of the dissolving sugar cube. This is how we tested our question. I expected the results that were gotten. Hypothesis: If temperature increases than the dissolving rate of a sugar cube will increase.

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6. ## AIM: To study the effect of solid impurities on boiling point of water and find the Molal Elevation Constant (Kb) and to calculate the percentage difference from accepted value for Kb.

I am making this project not only for marks but to also increase my knowledge. THANKS AGAIN TO ALL WHO HELPED ME. INTRODUCTION Boiling Point On heating a liquid its temperature rises gradually till a stage comes when the temperature does not rise further and the liquid starts boiling. The fixed temperature at which a certain liquid boils is termed as the boiling point of liquid. The boiling point of water is 1000C or 373 K. In terms of vapour pressure the boiling point of a liquid is the temperature at which vapour pressure of the liquid becomes equal to the atmospheric pressure and the liquid changes into a vapor.

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7. ## Ethanoic Acid Titration

The commercial vinegar was diluted by pipetting 25.0mL of the vinegar into a 250mL volumetric flask. The mark was later met with demineralised water by using a small glass pipette for accuracy. The 250mL volumetric flask was then mixed thoroughly by shaking it with inversion and swirling. The 25.0mL pipette was rinsed thoroughly with demineralised water. It was then rinsed with the diluted vinegar solution. 25.0mL of the diluted vinegar solution was pipetted into each 100mL conical flask with 4 drops of phenolphthalein indicator. The burette and plastic funnel were rinsed with the sodium hydroxide solution.

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8. ## Chemistry revision notes - 4 methods of making salts.

+ Mg(s) ? MgCL2(aq) + H2(g) Hydrochloric Acid + Magnesium ? Magnesium Chloride + Hydrogen Method 2 : Acid + Insoluble Base 1. Neutralisation reaction 2. When Acid and Base react ? Salt and Water is formed 3. The salt made depends on the acid used and the metal in the base/alkali - (e.g.

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