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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. Does the concentration of hydrochloric acid affect its rate of reaction with calcium carbonate?

A catalyst will not be used in this reaction, however. * Mass of marble chips - the mass of the marble chips is a way of measuring the quantity of chips being used. * Temperature - an increase in temperature adds energy to the reaction by increasing how quickly the particles move. By doing this, temperature affects the number of affective collisions. * Light intensity - the light intensity has a very small affect on the experiment so will not be measured in this experiment. Key Element to keeping this a fair test It must be ensured that all the variables must be kept at a specific level, apart from the one variable that I will be investigating the effect of.

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2. Making a Halogenoalkane

NaHSO4 + HBr There is also an unwanted side reaction that takes place at this stage. That is the oxidation of the product we want, the HBr into water and bromine: 2HBr + [O] ? H2O + Br2 (It does serve some purpose in colouring the halogenoalkane, which later on will be useful). The oxidising agent is the sulphuric acid, which is reduced to sulphur dioxide amongst other things. As I will explain later, the conditions of the first reaction will have to be configured so that production of HBr is maximised, and so that the oxidation of HBr is minimised.

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3. Investigate whether the concentration of acid effects the speed of the weathering of limestone

I will keep all bags tucked under the desks so no-one trips over them. I will always wear goggles and an overall while handling acids, as they can be corrosive and dangerous. If I do spill any acid on myself, I will wash it off immediately without coming into contact with anyone else.. I will make sure that I conduct the experiment in the middle of the bench so that it cannot be knocked off the edge. I will try make sure that the experiment is performed with great care and that all safety regulations are followed.

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4. Investigating the effect of a chosen factor on the activity of Lipase

Secretion of Bile salts and Lipases into the stomach, 2. Emulsification of Lipids with the Bile salts 3. The enzymatic hydrolysis of the ester linkages in the triglycerides with the Lipases 4. The formation of lipid containing bile salt micelles which transport the lipids to the cells for resynthesis or oxidation The use of Bile salts is required because lipids form non-polar structures that are insoluble in water. As water is the main medium of digestion in the lumen, this will pose some difficulty as the water soluble enzymes will not be able to digest the lipids efficiently unless they are somehow broken up in the water mechanically so that there is greater surface area to react with.

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5. An Experiment Into the Thermal Decomposition of Metal Carbonates

This is the equation for the thermal decomposition of Copper carbonate. CuCO3 + heat energy = CuO + CO2 The Factors affecting the experiment are: 1. Temperature The temperature must be kept constant throughout the entirety of the experiments. This means using the same Bunsen burner on the same setting on the same gas tap for each experiment. The flame should be at a blue flame, but not roaring, as this can break the boiling tubes, broken glass is a hazard. Another reason is that if it is on a roaring flame, the reaction will take place too quickly for you to be able to take a desired amount of readings.

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6. The Biology and Diversity of Extant Reptiles.

Adaptations to withstand desiccation Unlike amphibians reptiles are able to tolerate dryer conditions and avoid desiccation. This allowed them to exploit more niches and therefore achieve greater radiation. They did this in a number of ways: 1 Skin. Reptilian skin is impermeable to water due to its unique structure. It has a thick dermis and a thick epidermis. The relative thickness of these layers helps somewhat in water conservation but it is the components of the epidermis that make the skin waterproof. See diagram: The ?-keratin makes up the lower layer and is softer and more pliable then the darker harder �-keratin layer.

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7. Investigating the Chemistry of Group 1 and 2 Elements

The thermal stability of the carbonates of Group 2 elements increases as you move down Group 2 with Magnesium carbonate being the most unstable Group 2 carbonate tested and Barium Carbonate being the most stable Group 2 carbonate tested. e) The general equation for the thermal decomposition of Group 2 Carbonates, where M stands for a Group 2 element is; MCO3 MO + CO2 f) Limewater is used as a partially quantitative test for Carbon Dioxide. When Carbon Dioxide is passed through Limewater, Calcium Carbonate is produced in the form of a white precipitate Calcium Hydroxide + Carbon Dioxide Calcium

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8. Reactivity of metals Investigation

* Dilute bench acid (Hydrochloric acid - HCL) The above apparatus will be cleaned out before use to create a fair test. Safety For safety reasons I will need to wear safety spectacles at all times when conducting my experiments. I will set up the apparatus on a Bunsen burner mat so that no chemicals leak onto the bench. This is because we will be dealing with hot substances and acid. Hydrochloric acid can be: Explosive Flammable Corrosive Harmful Method I set up the apparatus and placed it on a Bunsen burner mat so chemicals wouldn't leak onto the bench.

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9. Investigation into the effects of concentration of reactants on the rate of reaction.

I am also going to use a 5ml syringe to measure the acid in. Equipment that that I will use in actual experiment that wasn't available for trial run are: Burettes, stop watches (not stop clocks), a syringe for the acid and a water bath to help keep temperature constant throughout all reactions. Control of variables The following variables will be controlled: - Temperature- If the temperature is increased or decreased the rate of the reaction would increase or decrease with the temperature.

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10. An Investigation of the weathering of limestone.

Safety: In the experiment I will be as safe as possible. I will tie back my hair to keep it from falling into the experiment, wear my overall to protect my clothes from the acid and wear goggles over my eyes to protect them, also from the dangerous acid. I will make sure that stools and bags are carefully stowed away so that we do not trip over them. I will also make sure that the experiment is in the centre of the table so nothing will be able to easily get broken or fall on my toes!

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11. What Factors Affect the Rate of Reaction Between Hydrochloric Acid and Calcium Carbonate?

are exposed to any substance it may contact. The molecules on the right are the original solid divided into smaller pieces. There are the same number of molecules but all of them are exposed. Another factor which will affect the rate of a reaction, is the concentration of the substances, in this case hydrochloric acid. The acid solution being used is made from concentrated hydrochloric acid, diluted with water and then halved continually with more water, until the correct concentration is obtained. The concentration of acid is measured in moles/litre 1 Mole =The atomic mass of the substance's formula in grams per 1000cc of solution, the rest being water.

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12. 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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13. 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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14. 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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