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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. ## Period 3 Elements.

* Table salt. Magnesium (Mg) Magnesium is silvery white in colour and is a solid at room temperature. It is conductive to both heat and electricity. It has a melting point of 922 K and a boiling point of 1378 K. There are many minerals containing magnesium including magnesite and dolomite. Sea water also contains plenty of magnesium. Magnesium is the eighth most abundant element in the earth's crust although not found in it's elemental form. Magnesium tarnishes slightly in air, and finely divided magnesium readily ignites upon heating in air and burns with a dazzling white flame.

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2. ## Investigate the heat of neutralisation when an acid and an alkali (a soluble base) are reacted together.

Neutralisation happens when all the H+ and OH- ions are turned into water. Procedure I will carry out the experiment as follows: 1) I measured 50cm3 of the desired alkali into a conical flask. 2) Then placed the alkali in a polythene cup. 3) The polythene cup was then placed inside a beaker, in case if the cup leaked it wouldn't spill all over the bench. 4) I then measured 10cm3 of acid using a measuring cylinder. 5) I poured the acid in the cup and measured the temperature. 6) I do the exact same thing as in step 5 until I have added 90cm3 of acid, measuring the temperature each time. 7)

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3. ## Investigate the effect of changing the hydrogen peroxide concentration on the rate of reaction of the break down of hydrogen peroxide by catalase.

The volume of catalase 4) The amount of time the experiment will go on for 5) The apparatus I will use during the experiment. I must make sure I use the same apparatus each time. *The One factor that I will deliberately change. 1) The concentration of the hydrogen peroxide. I will lower its concentration each time by adding it with measured amount of distilled water. I will change the concentration 11 times. *The factors that I will keep constant (Fair Test)

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4. ## To find the resistance of wire.

To make the experiment a fair test I am going to keep the temperature, the thickness, the voltage, the current and the type of wire all the same. By doing this my results will be kept controlled and none of my results will be influenced by other things such as thickness or current. Prediction I predict that when I change the length of the wire the resistance will @-)---- After researching using books and the internet I have found more detailed scientific knowledge to explain my prediction: In order for things to react together their particles must collide with each other and must be charged with enough energy.

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5. ## This experiment will show how the temperature and concentration affects the rate of reaction between sodium thiosulphate and hydrochloric acid.

However in 50cm3 of sodium thiosulphate there would be more molecules present so the chance of collision is higher meaning the reaction would be subsequently quicker. My final reason for my prediction brings the kinetic theory into my experiment this theory tells us that the higher the temperature a substance is the greater kinetic energy it has, which in a liquid means the molecules can move around quicker. This relates to our experiment because if the molecules are moving around faster they will collide more often meaning the reactions will happen more rapidly.

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6. ## An Experiment to Determine the Enthalpy Change for the Decomposition of Calcium Carbonate.

CaCO3(s) CaO(s) + CO2(g) ?H? CaCO3(s) CaO(s) + CO2(g) R2 + 2HCl acid + 2HCl acid R1 CaCl2(aq) + CO2(g) + H2O(l) From here I can clearly see two different routes in which I will conduct my experiments from (route 1 and route 2). ROUTE 1 Diagram for Route 1 Apparatus Needed The apparatus, equipment and chemicals that is needed for this experiment is: 1. 100cm� measuring cylinder 2. 250cm� beaker 3. Polystyrene beaker and lid 4. A weighing bottle 5. Thermometer Substances Needed 1. Calcium Carbonate (CaCO3) 2. Hydrochloric acid-HCl (2.0 mol dm� �) The amount of substance I chose to use was 5.0 grams of calcium carbonate because from the equation CaCO3(s)

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7. ## An investigation into how changing one variable influences the rate of reaction between marble chips and hydrochloric acid.

If you double the strength of the solution, the rate of reaction will double. 2. A list of variables I will attempt to keep constant. * I will attempt to keep the temperature constant by doing my experiment in the same area and doing all the experiments at a certain time of day so there will not be many or any temperature fluctuations. I made sure of this by keeping a thermometer present at all times to check whether there were any temperature fluctuations.

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8. ## The aim of this investigation is to investigate the time that it takes the jelly block to completely dissolve in water.

If there are more water molecules in the container that means that there will be more molecules that will bombard the jelly mass. Therefore one jelly molecule will be pulled out by more water molecules than before producing a stronger pull between the water molecules and the jelly molecule. This means that the more water, the quicker the time for the jelly to dissolve. If there is less water then there will be less water molecules so the dissolving will be much more slower.

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9. ## To see how fast magnesium reacts in different molarities of Hydrochloric Acid.

We started the stopwatch just as the Mg strip was put in, to be certain of the time. For the first experiment Method: - 1. First of all I will gather all my apparatus in to one place. 2. Then I will place the conical flask on top of a white paper, this will make the image clearer. 3. I will then use emary paper to take away all impurities from the magnesium strips, and then cut them in to 3cm strips.

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10. ## My Aim is to see how concentration of acid will affect the time it takes for Sodium Thiosulphate to become cloudy and make a cross below it to disappear.

1. Put the black cross underneath the 250cm � Beaker, leave this on the side. 2. Measure out 50cm � of Sodium Thiosulphate in the 100cm � Measuring cylinder and pour into the 250cm � beaker 3. In the other 100cm � measuring cylinder. The volume of Hydrochloric acid +volume of distilled water add up to 10cm �. Here is a table 4. Put the black cross underneath the 250cm � Beaker, leave this on the side. 5. Measure out 50cm � of Sodium Thiosulphate in the 100cm � Measuring cylinder and pour into the 250cm � beaker 6.

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11. ## The aim of this experiment is to determine the rate of reaction between thiosulphate(Na2S2O3) and various concentrations of hydrochloric acid (HCl).

Therefore, the only variable in this experiment will be the ratio of the concentration of the hydrochloric acid and thiosulphate. To vary this, I will dilute the acid with different amounts of water, changing the ratio of acid to water. Below are the ratios I will be using: Acid (ml) Water (ml) 0 50 (All water) 10 40 (Considerably more water than acid) 20 30 (Slightly more water than acid) 30 20 (Slightly more acid than water) 40 10 (Considerably more acid than water)

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12. ## This survey was concerned with looking at the changes in soil and vegetation on a transect located at Dead Mans Hill (See map A). The aim was to record the type and quantity of vegetation and to analyse the quality of soil on the transect.

Surface water was visible which had a brown /orange colour. The only wildlife visible was New Forest ponies, which roam freely over the forest. Signs of a rabbit population were also visible. Heathland is only found in temperate climates in Western Europe below an altitude of 300m and is an important habitat for animals such as the Nightjar, Stone-curlew, Dartford Warblour and Smooth Snake. Heathland is not a natural landscape; there is evidence of it being present as far back as the Bronze Age. Earthworks such as barrows and other structures were sited on the heath so as to be seen from a distance; the soils beneath these earthworks contain podzols, which only form where ling is present on heathland.

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13. ## Finding out how much acid there is in a solution.

Add anhydrous sodium carbonate and leave to react, and then add plenty of water. Sodium carbonate - Irritant (to eyes, skin and respiratory system) - If swallowed wash out mouth with water - If it gets in eyes flood the eye with water for 10 minutes - If solid is spilt, scoop up and rinse area with water. If in solution, cover with mineral absorbent, put in bucket, and rinse the area with water. I will wear a lab coat and goggles to protect my skin, clothes and eyes. To make up a standard solution of 0.100 mol dm-3 sodium carbonate.

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14. ## Thermochemistry - calorimetric determination of the dissociation energy of hydrogen peroxide.

51.46 4. O2(g) + H2(g) ? H2O(l) -285.9 5. H2O(l) ? H2O(g) 44.02 6. H2(g) ? 2 H(g) 436.0 7. H2O(g) ? OH(g) + H(g) 498.8 II. INTRODUCTION Adiabatic calorimetry will be used in this experiment to determine the molar heat of decomposition DHdec of hydrogen peroxide. Adiabatic means that there is no heat flow out of the system. H2O2(aq) ? H2O(l) + O2(g) DHdec (2) In adiabatic calorimetry, the heat change that is caused by the reaction of interest is confined to a reaction vessel called a calorimeter.

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15. ## Urology - Explain the following terminologies and what equipment is required for each:(a) TURP - Trans-Urethral Resection of Prostate.

Can relieve water retention. Equipment; As above - plus a Collins knife. (c) TURT (TURBT) - Trans-Urethral Resection of Bladder Tumour. Again a cystoscope is used to view the bladder. If a raised lesion is detected the resectorscope is used to burn it away, using a diathermy loop, and a rollerball for haemastasis. Equipment; As above (a) (d) Cystoscopy/Cystodiathermy - A Cystoscope is used to examine the the bladder, bladder neck, trigone, prostate, and posterior wall of the bladder, using light and camera on a tower system and monitored on a screen.

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16. ## Determination of the relative atomic mass of Lithium

2Li (s) + 2H2O (l) 2LiOH (aq) + H2 (g) Ar = m � n n = V � 24 = 0.11g � 0.0155 = 0.186dm3 � 24 = 7.096774194 = 0.00775 mols = 7.10 gmol-1 (3sf) (3sf) 2 : 1 0.0155 mols 0.00775 mols Figures in bold type are seen in the results table above. All answers are accurate to 3 significant figures. * To find the volume of hydrogen, I had to substitute the volume (V) to the volume of hydrogen (which I entered in my results table), which was 0.186 dm3 into the formula n = V � 24, in which I got the answer 0.00775 mols.

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17. ## Testing Salt Solutions to See What They Contain

in the tube would not interfere with the current tests, and the wire for the flame test should be properly cleaned for the same reason. The exact same method should be used for each similar test, so that the same sorts of results are obtained. Methods For this experiment there are several methods as several tests need to be performed. During this section I shall introduce each test, and how it should be performed. Flame Test: Firstly a bunsen burner will need to be set up, and then a wire on a cork will need to be obtained.

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18. ## What effect does Acid rain have on germination?

A typical seed stores carbohydrates, lipids and proteins. It also stores minerals and vitamins. As a result of 'imbibition' (the initial uptake of water by a seed) and osmosis (water travels from cell to cell in the seed by osmosis) the embryo becomes hydrated and this activates enzymes. The enzymes then break down the food reserves the seed needs for growth. Proteases Proteins Amino acids Carbohydrases Polysaccharides Sugars Amylase Maltase Starch Maltose Glucose Lipases Lipids Fatty Acids + Glycerol The soluble products of digestion then go to the growth regions of the embryo, enabling the seed to grow.

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19. ## Studies On Vitamin C Degradation in Fruit.

The minimum intake in infants to prevent scurvy is around 10mg per day. Workers in very cold climates should have an intake of around 150-250 mg per day. To complete the discussion of biological significance here Ascorbic acid is required for the formation of hydroxyproline and collagen with insufficient hydroxyproline is unstable. The triple helical structure of this tissue is known to fall apart and the protein is rapidly degraded. This results in loss of connective tissue. Early symptoms of scurvy include loss of weight, anaemia and fatigue.

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20. ## Calibrating pH meters

We will make sure the ph meter is calibrated by using a buffer solution to calibrate which has a guaranteed allowance of 0.001 from ph7.The purpose of this experiment is so that we can successfully use and understand pH meters. My aim to receive accurate results and a calibrated pH meter. Safety There are many safety issues that arise when dealing with chemicals and laboratory's that is why when conducting an experiment all safety aspects need to be thought about before carrying out the experiment otherwise someone could occur contamination or a serious injury when conducting the experiment.

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21. ## Deducing the quantity of acid in a solution

I will weigh the first 250cm3 beaker, and reset the balance to 0. 2. I will transfer about 2.65g of solid anhydrous Na2CO3 into this beaker (weighed to the nearest 0.01g). 3. I will put about 50cm3 of distilled water into the second beaker and then carefully transfer the bulk of Na2CO3 from the first beaker into the beaker of water. 4. I will then reweigh the first beaker to find out the amount of remaining Na2CO3. 5. Using a glass rod, I will stir the solid and water in the beaker to dissolve, adding more water as is necessary.

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22. ## The Concentration of Limewater Solution.

of Moles = 6.746 x 10-4 = 3.373 x 10-4 dm3 = 0.337 cm3 Concentration 2 So 0.337 cm3 of 2.00mol dm-3 hydrochloric acid will neutralise 25.00cm3 of the limewater. However, 0.337 cm3 is not a measurable using a burette and is far too small and inaccurate, 30.00cm3 would be a measurable volume using a burette, so I will now calculate how much to dilute the 2.00mol dm3 hydrochloric acid by, to make the approximate volume that will neutralise the 30.00cm3 limewater.

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23. ## Indirect determination of enthalpy change of decomposition of sodium hydrogen carbonate by thermochemical measurement and Hess's Law.

? Should spillage occur, again notify supervisor and dilute with water before mopping up. ? Sodium carbonate is an alkaline metal and poses a hazard. Should it come into contact with skin, wash immediately with copious amounts of water. ? Throughout the experiment safety goggles and a lab coat should be worn. Eyes are a highly sensitive region of the body and care should be taken to protect them. ? Care should be taken when using the thermometer. It is important that it is not broken or damaged, as it contains mercury, and the vapour from mercury is a cumulative poison.

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24. ## Acids, water and oxygen can all weather rocks. They break down the rocks by reacting with, or dissolving, some of the materials in the rock.

It thermally decomposes when heated strongly. Calcium carbonate, in limestone and marble, reacts with acids. For the purpose of our experiment we will be using marble chips and hydrochloric acid. Calcium carbonate + hydrochloric acid ? carbon dioxide + water + calcium chloride Heat is given out in an exothermic reaction. We know this because the surroundings get warm. In an endothermic reaction, energy is taken in from the surroundings. The surroundings then have less energy than they started with, so the temperature falls.

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25. ## I will identify the unknown cations from the alkaline earth metals.

1-cm length of 24 gauge of aluminum wire 16. Centrifuge 17. Hot pads 18. Metal spatulas 19. Medicine droppers 20. Test tube holders V. Procedure: Group I Cations Step 1: 1. Add 0.5 ml 6 M HCl to 3 ml of a sample in the test tube. 2. Stir well and centrifuge. 3. Decant the liquid, which may have ions, into a test tube. 4. Save the test tube for further analysis. 5. Make sure precipitation for Group I cations was complete by adding 1 drop of 6 M HCl into the liquid. 6.

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