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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. ## I have been supplied with an unknown organic compound containing one of the following functional groups: Alkene Primary alcohol Tertiary

Indication of a positive test The orange solution turns green, as the orange dichromate (VI) ion, is reduced to green chromium(III) ion. 3) Test for the presence of a tertiary alcohol Heat the unknown organic compound gently (reflux) with acidified potassium dichromate (VI), which is an oxidising agent, and concentrated H SO in distilling apparatus. Indication of a positive test No formation of an aldehyde or a ketone, as tertiary alcohols cannot be oxidised. 4) Test for the presence of a carbonyl group 2,4-dinitrophenylhydrazine (DNPH) test shows a positive test for aldehydes and ketones It reacts with the carbonyl group of the aldehydes and ketones.

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2. ## The objective of this experiment is to calculate the % purity of aspirin, by first neutralizing the acetylsalicylic acid with excess sodium hydroxide, and then back titrate the excess

25 cm3 of the above solution was pipetted into a conical flask. 5) A titrating burette was then set up. First of all it was rinsed with the 0.1 M HCl, before the whole burette was filled with the acid. 7) Three drops of phenolphthalein to the conical flask. The solution is now pink in colour. 6) The base solution in the flask was the titrated with the HCl till the colour became colourless, which is the end point.

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3. ## Preparing benzoic acid from benzylalcohol

After the some time, we filter it through a B�chner funnel before it is recrystallized and filtered again. The mass was recorded as it was dry. By adding sodium carbonate, we will now test whether what obtained is benzoic acid or not, because one can observe bobbles if it is an acid. After that we burn it to test if it is aromatic. Soot would be possible to obtain if it was to be aromatic. Data Collection Mass of benzylalcohol 3.991 grams Mass of flask (before adding benzoic acid) 95.47 grams Mass of flask (after adding benzoic acid)

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4. ## Huddling sheep In this experiment I plan to do 10 different tests, to discover the effects of huddling.

on some blue tack (blue tack is used to reduce conduction through the base of the test tube). * If more than 1 test tube is used place an elastic band round them (to reduce the chance of the test falling over) * Fill each test tube with boiling water, placing a thermometer in the centre tube (when water has been added).

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5. ## I am to determine the concentration of limewater solution by Titration method.

* Distilled water * Methyl orange used as an indicator Firstly put the alkaline calcium hydroxide solution in the flask and the hydrochloric acid in the burette. Next you need to construct the relevant equation: Ca(OH)2 + 2HCl ----> CaCl2 + 2H2O The above equation tells us that 1 mole of calcium hydroxide reacts with exactly 2 moles of hydrochloric acid, so we should try to make the solution of HCl about twice as concentrated as the Ca(OH)2, so that when we measure out, shall we say, 10 cm3 of the calcium hydroxide solution into the flask we should need to add approximately 10 cm3 of hydrochloric acid from the burette.

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6. ## Experiment to measure the Specific Heat Capacity of Water

* The current was measured in the ammeter and recorded. * Water was left to heat for 10 minutes. * The final water temperature was recorded. Results and Calculations Voltage, (V) 12 V Current, (A) 1.3 A Time, (S) 600 s Energy, (J) (VxTxI) 9360 J Mass of water, (Kg)

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7. ## Osmosis Project

We will change the strengths of the solution and then weigh the carrots to see if they are heavier and have absorbed more water and solution. We can change the strengths of the solution by adding water to the solution to weaken it meaning the more water the weaker the solution. We will record our results and then repeat the experiment to make sure the results are correct and accurate. I will put different strengths of solution into five beakers and then put five equally cut carrots into the solutions.

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8. ## Effect of temperature on rate of reaction

Method: The experiment has to be done five times for the five different temperatures of the sodium thiosulphate. The temperatures are: 20�C, 30�C, 40�C, 50�C and 60�C To start the experiments fill the flask with 50cm� of sodium thiosulphate into the large beaker. Fill the large beaker up with the water of right temperature that is required for the experiment. Put the thermometer into the flask with sodium thiosulphate and check the temperature is right for the experiment. If the water is too cold, in the large beaker pour in some more hot water or if it is too hot pour in some cold water to reach the required temperature for the sodium thiosulphate.

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9. ## AIMIdentify anions present in various salts by chemicals testing

These substances are dangerous with material like sugar, wood, clothes and etc. these solution ignite easily burn vigorously when dry. This should not be made available in the lab with concentrated sulphur. Iron chloride Sodium sulphate Harmful if swallowed. Irritant to eyes skin and respiratory system. Calcium carbonate Irritant to eyes. Avoid raising and it also irritant to eyes. Keep it away from water it could cause water to boil if because of the salt. Contact with combustion material may cause fire. Lead carbonate Harmful if inhaled or swallowed. Danger of cumulative effects.

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10. ## Flame test AIMCarry out test on different compounds and write down what it looks like.

Keep it away from water it could cause water to boil if because of the salt. Contact with combustion material may cause fire. Lithium sulphate Reacts violently with water and acids liberating a highly flammable gas (hydrogen). Can cause burns and it reacts vigorously with water to form lithium hydroxide which is corrsive.it reacts dangerously with nitric acid and ignites on contact with metal. Irritant to eyes and skin also harmful by ingestion in quantity and effect of ionic balance in the blood. Sodium carbonate Irritant to eyes skin and respiratory system. Potassium chloride Explosive when mixed with combustion materials. Never use fabric gloves to handle substance.

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11. ## To Determine the Concentration of Limewater

Tie back long hair ? Wipe any spillages with a bench cloth ? Rinse well with water any skin in contact with undiluted HCl. ? Wash your hands when you have cleared away Method: Diluting: 1.) Rinse the volumetric pipette, flask and stopper, a 100cm3 beaker, funnel and teat pipette with distilled water. 2.) Rinse 100cm3 beaker with HCl and pour into a labelled waste beaker.

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12. ## To investigate the effect of temperature on the volume of a gas

Variables: * Input(Independent): Temperature T/?C * Output(dependent): length of air column, L/cm * Controlled Variables: pressure and mass of gas inside capillary tube. Materials Needed: Clamp Stand Beaker 500ml Distilled water Bunsen burner 30 cm ruler Concentrated Sulfuric acid Glass tube Syringe needle Thermometer Method: * Heat the end of the glass tube so as to close it. The tube's end will melt and close. Make sure the end is blocked very well. * Using a syringe needle, inject approximately 1cm� of Sulfuric acid into the blocked glass tube.

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13. ## Hydrogen atoms can react with oxygen atoms forming different compounds. There are mainly two types, one is water and the other is hydrogen peroxide

For water at 1 atm, the melting point and boiling point is 0�C and 100�C respectively. Water reaches the maximum density at 4�C. The density of ice is lower than that of water. The molecules are in constant motion and the strong hydrogen bonding leads to the closed packing of water molecules. The melting curve of water in the phase diagram has an unusual negative slope. When the pressure of water increases, its melting point decreases. This is because high pressure reduces the volume of water and this is achieved by changing ice to liquid water.

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14. ## In the first experiment we noticed how Phenolphthalein, thiosulfate and copper (II) sulfate changed their physical properties once mixed with NaOH, Iodine and Ammonia

The amounts calculated according to stoichiometry are called theoretical yields whereas the actual amounts are called actual yields. The actual yields are often expressed in percentage, and they are often called percent yields. In this experiment we combined sulfuric acid and aqueous barium chloride to produce a precipitate, barium sulfate and hydrochloric acid. The precipitation was isolated by filtration and theoretical yield was calculated. We predicted the limiting reactant and verified our hypothesis in the lab. II. RESULT ANALYSIS DATA TABLE Table 1 Trial 1 Trial 2 Assigned volume of BaCl 30 mL 5 mL Actual mass of BaSO isolated 0.7g 0.17g Table 2.

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15. ## "Examine the impact that weathering has had on human activity."

This rain has then fallen on buildings such as St. Paul's Cathedral and increased chemical weathering leading to deterioration on its surface. Also, if cracks and joints present will have allowed this rain to enter and chemically weather there as well as on the surface. This chemical weathering has also been enhanced due to the extremely large presence of birds in the area, particularly pigeons whose faeces contribute to the chemical weathering. Very recently this has had an impact because it has been such an economic cost of �40 million to restore the western front of the building.

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16. ## The group two elements consist of Beryllium, Magnesium, Calcium, Strontium, Barium and Radium

The chemical properties of Group 2 elements are dominated by the strong reducing power of the metals. The elements become increasingly electropositive on descending the Group. The last element in Group 2, Radium, is not yet definite in terms of melting points or density due to its very strong radioactivity emission. Beryllium is used for X-ray windows (Beryllium transmits X-rays 17 times better than aluminium), as a 2% alloy with nickel for springs, electrodes and non-sparking tools. Beryllium (2%) alloyed with copper gives a hard strong alloy with high resistance to wear used in gyroscopes, computer parts, and instruments.

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17. ## To determine the concentration of a sodium carbonate solution

The apparatus needed for dilution of the acid:- * Labels- so we can tell which beaker contains what. * 2x Beakers- to hold the acid. * 1x 10cm� pipette - to pipette the acid with. * 1x Filter funnel - to pour the dilute hydrochloric acid through. * 1x Standard flask- to hold 250cm� of solution * 1x Dropping pipette- to put water in and drop it in to the standard flask if needed. * 1x Safety glasses- to protect eyes (from chemicals etc).

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18. ## Burning fuels investigation

of alcohol before experiment Fair Test To make it a fair test: * I made sure I put the same amount of water in the copper can. * I made sure that the water started with the same temperature with the same alcohol. * I made sure that the height was the same from the water to the thermometer. Health and Safety * Wear goggles * Hide tie in the shirt * Keep bags under the table Method I first got all the apparatus that I needed and set it up.

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19. ## How changing acid concentration changes the rate of reaction.

Apparatus 1 Conical Flask 2 Beakers 3 Measuring Cylinders Paper with a black cross on Stopwatch Nitric Acid Sodium Thiosulphate Water Safety Glasses Method For my experiment I will measure out 25cm� of Sodium Thiosulphate and put it in a conical flask. I will put the flask on top of a piece of paper that has a black cross drawn on it. I will then measure 15cm� of Nitric Acid and add this to the Sodium Thiosulphate in the conical flask.

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20. ## Preparation of Primary Standard and Acid Base Titration

Clean all the glassware involved in this experiment (e.g. burette, pipette, conical flasks, weighing bottle, volumetric flask, etc.) with deionized water as directed by the teacher. 2. Weigh by difference to collect the required mass (2 to 2.5g) of ethanedioic acid-2-water crystals. 3. Pour the weighed crystals into a dry clean 100 cm� beaker and add deinoized water to dissolve the crystals. 4. Wash the weighing bottle with deionized water and pour the rinse into the beaker also to ensure no loss of acid crystals. 5. Pour the content of the beaker in a clean 250 cm� volumetric flask and add up to the mark with deionized water. 6.

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21. ## Preparing a solution of sodium Chloride

spilt on floor: Scoop up and clean surface If spilt on skin or clothing: Wash off Hazard sign reads: Irritating Method and Materials 1. Using a set of scales I weighed out 14.625 grams of sodium chloride on a piece of filter paper 2. I then transferred the sodium chloride in to a 250ml beaker. 3. I then rinse the filter paper with distilled water to make sure that all the sodium chloride was in the beaker by collecting the washings.

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22. ## Experiment: To determine the correct equation for the decomposition

Cu2O (s) + 2CO2 (g) + 1/2 O2 (g) Equation 2: CuCO3 (s) CuO (s) + CO2 (g) I will do this by decomposing the copper carbonate. I will need to calculate if the volume of carbon dioxide produced is equal to what the equation suggests. Equipment: * Heatproof mat * Bunsen burner * Boiling tube * Bung * Delivery tube * Water bath * Measuring cylinder (250 cm�) * Digital weighing scales * Spatula * Clamp and stand * One molar copper carbonate (1 gram)

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23. ## I am going to investigate how concentration and temperature affects the rate of reaction between magnesium ribbon and hydrochloric acid.

Planning The equipment I will need is: * Goggles for eye protection * Beaker to put acid and water in * Stop clock for measuring the time * Magnesium strips to put in the solution the magnesium strip will be 3cm * Acid to mix with the water * Water to mix with the acid * Measuring cylinder to make the experiment accurate VARIABLES When I do my experiment I will change the concentration of the acid but when the acid and water are mixed together I will always keep the concentration 50ml3 I will keep magnesium strips the same size which is 3cm long.

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24. ## Determination of the relative atomic mass of lithium

H2 (g) I am going to calculate the number of moles of hydrogen, H2 that I had collected: No. of moles = V� 24000 V = amount of hydrogen collected 1: 173�24000 = 0.0072083mols (Li) 2: 176�24000 = 0.0073333mols (Li) I will now deduce the number of moles of lithium that reacted: 2 x molls of H2 1: 0.0072083 x 2 = 0.0144166mols 2: 0.0073333 x 2 = 0.0146666mols Now I have these results I will calculate the relative atomic mass of lithium. RAM = mass of lithium � no. of moles 1: 0.09 � 0.0144166 2: 0.09 � 0.0146666 = 6.24 (3s.f)

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25. ## The Effect of Concentration on the Rate of a Reaction

MEASUREMENTS * Magnesium ribbon = 4cm each time * HCl solution= 1. 20ml of 2M HCl 2. 15ml of 2M HCl, 5ml of water 3. 10ml of 2M HCl, 10ml of water 4. 5ml of 2M HCl, 15ml of water 5. 20ml of water (this is the control) DIAGRAM RESULTS These are the results we obtained for the experiment: TIME TAKEN FOR MAGNESIUM TO STOP FIZZING (S) SOLUTION TRIAL 1 TRIAL 2 AVERAGE 20ml of 2M HCl 36.30 36.98 36.64 15ml of 2M HCl, 5ml of water 44.75 67.40 56.075 10ml of 2M HCl, 10ml of water 128.59 89.14 108.865 5ml of 2M HCl, 15ml of water 700.65 670.08 685.365 20ml of water (magnesium did not dissolve)

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