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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. ## Biology Practical Investigation to find the lowest concentration of Copper Sulphate solution that will denature egg albumen.

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The third bond is the hydrogen bond, which occurs between hydrogen and oxygen atoms within the polypeptide chain. Hydrogen bonds are not strong on their own, although a large number of them together makes them very strong. The primary structure is the linear sequence of amino acids stablised by peptide bonds. There are an endless number of different possible primary structure The secondary structure is the sequence of amino acids arranged as either an alpha helix of a beta pleated sheet stabilised by peptide s.

• Word count: 804
2. ## Back Titration Lab Report. In my experiment, I hoped to find the amount of calcium carbonate in some mineral limestone using the back titration method

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250 cm3 volumetric flask (� 0.2 cm3) 50.0 cm3 burette (� 0.05 cm3) 25. 0 cm3 pipette (� 0.1 cm3) 3 x conical flasks Clamp and retort stand 1.0 mol dm-3 hydrochloric acid, HCL 1.5 g of limestone phenolphthalein indicator 0.1 mol dm-3 Sodium hydroxide, NaOH Method: When I had all this, I started my investigation by weighing 1.5 g of limestone on the electric balance. After obtaining the weighed crystals I dissolved them with 1.0 mol dm-3 hydrochloric acid, in the beaker provided and stirred the mixture till bubbling stopped.

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3. ## Analysis of Neutralisation of NaOH

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If there were more hydroxide ions than hydrogen ions then once every hydrogen ion joined with 1 hydroxide ion there would be hydroxide ions left meaning the solution would become alkaline. When an acid contains more hydrogen then there are a greater number of hydrogen ions per ml than in an acid containing less hydrogen so it will be stronger. For example in sulphuric acid (H2SO4) there would be more hydrogen ions than in the same amount of hydrochloric acid (HCl), twice as many because there are twice as many in the formula.

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4. ## The aim of the experiments was to test food samples to see which food group the sample belongs to. I also did tests to determine what type of carbohydrate an unknown carbohydrate was.

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* Pipettes Benedict's Test for non-reducing sugars * Benedict's reagent * Non-reducing sugar sample e.g. sucrose * Test tubes * Water bath or heating apparatus * Pipettes * Hydrochloric Acid * Alkali powder (sodium hydrogen carbonate) Starch Test * Starch Sample * Iodine * Tray * Pipette Emulsion Test * Ethanol * Lipid Sample * Water * Test Tubes Methods The Biuret test 1. Put about 2cm3 of the test sample into a test tube 2. Put an roughly equal amount of biuret's reagent into the same test tube using a pipette 3.

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5. ## My aim for this experiment is to investigate the solubility of salt

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Scientific Knowledge Salts contain positive and negative ions, which are held together by the strong force of attraction between particles with opposite charges. When one of these solids dissolves in water, the ions that form the solid are released into solution, where they become associated with the polar solvent molecules. H2O NaCl(s) Na+(aq) + Cl-(aq) We can generally assume that salts dissociate into their ions when they dissolve in water. Ionic compounds dissolve in water if the energy given off when the ions interact with water molecules compensates for the energy needed to break the ionic bonds in the solid and the energy required to separate the water molecules so that the ions can be inserted into solution.

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6. ## equilibrium constant

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acid present. 4. A few anti-bumping granules were added to the flask, and it was attached to a water-cooled reflux condenser. It was refluxed for 1 hour. The flask and its contents in an ice bath was cooled. 1.0 cm3 sample was removed from the flask for titration with the 0.50 M sodium hydroxide solution as before. The titre needed was recorded (V3)and was corrected for the sulphuric(VI) acid. 5. Refluxing was continued for an additional half hour, and was then cooled and was titrated another 1.0 cm3 sample.

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7. ## Oserving the properties of water. Place a drop of water on a smooth plastic sheet or on the bench. Look at it closely from the side.

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Experiment #2: Fill a clean 250 ml. beaker with water to about 1 cm. below the top. Carefully float a small filter paper on the surface. Carefully drop a needle, exactly horizontal, on the paper. Wait until the paper becomes soaked and sinks. Observe the needle carefully. After you have observed it, add one drop of detergent with a glass or plastic rod. * the piece of paper floats on the water and then it sinks because it get too wet.

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8. ## Handling Experiments,Observations and Data

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Heat the contents of the crucible gently at first and then strongly. 4. Remove the crucible from the burner when all the water of crystallization is removed from the copper sulphate crystals. 5. Allow the contents of the crucible to cool down. 6. Weigh out the crucible with its contents again until a constant reading is obtained. Table of Results Substance to be Weighed Weight in Grams Beaker alone 50.00g Beaker + copper sulphate before heating 52.50g Beaker + copper sulphate after heating 51.44g Observation: * The beaker was not directly over the fire and the blue copper sulphate crystals at the bottom of the beaker begin to turn white.

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9. ## To determine the concentration of a limewater solution

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Moles = Mass RMM Calcium = 40 Oxygen = 16 Hydrogen =1 = 1 = 1 40+(16�2)+(1�2) 74 = 0.0135 moles of calcium hydroxide The formula which the calcium hydroxide will react with the hydrochloric acid is: Ca(OH)2(aq) + HCL CaCl2(aq) + H2O(l) When balanced= Ca(OH)2(aq) + 2HCL CaCl2(aq) + 2H2O(l) The ratio in which the calcium hydroxide reacts with hydrochloric acid is 1:2. Therefore, to work out the mole of hydrochloric acid needed for this investigation is shown below: Ca(OH)2 + 2HCL Ratio = 1 : 2 Moles = 0.0135 : (0.0135�2)

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