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# GCSE: Aqueous Chemistry

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Meet our team of inspirational teachers Get help from 80+ teachers and hundreds of thousands of student written documents ## 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!

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1.  ## Chem MC analysis. In which of the following cases may it obtain a complete neutralization? (1)25.0 cm3 of 0.120 M sulphuric acid and 50cm3of 0.120M sodium hydroxide solution (2)50.cm3 of 0.5 M Sodium hydroxide and 0.025 moles of aqueous ammonium chlorid

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?Number of moles of solute (mol) = Molarity of a solution M or mol dm-3X Volume of solution (dm3) Number of moles of H2SO4 given: 0.12 X (25.0 /1000) = 0.003mol Number of moles of NaOH given: 0.12 X (50.0/1000) = 0.006mol Mole ratio of H2SO4 : NaOH = 0.003 /0.006 = 1:2 Therefore, option (1) is correct. Option 2 : NaOH(aq) + NH4Cl (aq)--> NaCl(aq)+ NH3(g) + H2O(l) Mole ratio of NaOH : NH4Cl = l :1 ?Using the formula, Molarity of a solution M or mol dm-3 = Number of moles of solute(mol) / Volume of solution (dm3)

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2.  ## To determine the amount of ammonia in a sample of household cleaning product, 'cloudy ammonia', in the form of NH4OH through the process of volumetric analysis.

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The end point of a titration is the stage at which the chosen indicator (methyl orange) changes colour to show that a reaction e.g. neutralisation has occurred. In theory, the equivalence point should equal the end point. Materials: * 1x 10ml Pipette * 1x 20ml Pipette * 1x Burette * 2x 250ml Volumetric flask and stopper * 3x Conical/Titration flask * Sodium Carbonate (Na2CO3) * 1x Electronic balance * Distilled water * Hydrochloric Acid * Methyl orange indicator * 1x Clamp and stand * 10ml of cloudy ammonia * 1x Glass dropper * 1x 50ml beaker * 1x Glass funnel

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3.  ## Conductivity Lab. Purpose: To determine which substances are ionic and which are molecular based on their ability to conduct electricity

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Also, ionic compounds dissociate while most molecular compounds don't 3. What does it mean when something "dissolves" in water? Is this the same as "dissociate"? When something dissolves in water, the substance bonds with the liquid. It is not the same as dissociation because dissociation is when the ionic bonds separate from each other. 4. Complete the table below based on the definitions given above and your understanding of ionic and molecular compounds. Material to be tested Prediction: will it conduct electricity? Why? Tap water Yes It is a common saying . Distilled water Yes It is probably has the same properties as tap water.

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4.  ## Types of Chemical Reactions

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Methods and Materials This experiment called for numerous testing, using a variety of different laboratory tools in addition to a few different substances and materials to perform reactions with. The first experiment (Reaction A), which was performed to become familiar with a synthesis reaction, involved the use of magnesium ribbon and heat provided by a laboratory burner. The magnesium ribbon was placed a crucible while the laboratory burner was in use. Forceps were used to hold the magnesium ribbon while the reaction was occurring.

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5.  ## ANALYSIS OF ASPIRIN BY BACK TITRATION

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INTRODUCTION Aspirin is an acid and can be determined analytically by the method of back titration. However aspirin is not soluble in water so cannot be titrated directly with an alkali. So the aspirin is reacted with an excess of sodium hydroxide, which produces a water soluble salt of aspirin. (The ester group also reacts, so two moles of sodium hydroxide are required to react with one mole of aspirin.) The excess alkali (which was left over from the above reaction) may then be determined by titration HCl + NaOH NaCl H2O The amount of alkali which is used up in the initial reaction with aspirin may be calculated, and this can be related to the quantity of aspirin.

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6.  ## Investigating The Rate Of Reaction Between Sodium Thiosulphate And Hydrochloric Acid

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The concentration of either Sodium Thiosulphate or Hydrochloric acid can be changed, I have chosen to change the concentration of the Hydrochloric Acid, I will change the concentration by adding the correct amount of water. I have decided to use a range of 5 different concentrations of Hydrochloric Acid 50-0cm3 going down in steps of 10. To change the concentration I am going to add water 0-50cm3 going up in steps of 10. The amount of Sodium Thiosulphate will be fixed at 10cm3.

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7.  ## Thermometric Titration Investigation

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Also to increase accuracy we used two molar instead of one molar reactants. This is because otherwise the differences in temperature would be hard to read to an accurate scale by eye off a mercury thermometer. It may of course be feasible with electronic digital thermometer which measures to several decimal places, which of course, with smaller changes from the room temperature, less inaccuracy would come from heat being lost. Energy Change = Temp Rise X mass of liquid X 4.2 (Joules)

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8.  ## The Haber Process

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However, if the conditions of the reactions such as temperature, pressure and concentration are modified, then the position of equilibrium may be changed. Using the graph, I am going to calculate the mass of Ammonia produced at various temperatures. This is the balanced equation used for the Haber Process: N2 + 3H2 2NH3 Using this balanced equation, I will calculate the 100% mass of Ammonia. I will begin by working out the Atomic Mass of the reactants within the balanced equation.

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9.  ## Rates of Reaction - Chemistry

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It was held in place with a clamp stand. We had to ensure that there were no air bubbles in the cylinder or the measurements that we took would be inaccurate because it wouldn't have begun with zero gas in the cylinder. We placed the end of the tube and bung into the cylinder and measured out the appropriate amount of hydrochloric acid and poured it into a boiling tube. Next, we cut a strip of magnesium down to 2cm long and put it into the boiling tube, placing the bung in immediately and starting the stopwatch.

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10.  ## Rate Of Reaction

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State of division: If you had lots of little chips and only a few big chips the smaller chips would react faster because there is more surface are, thus more particles, therefore more collisions take place. Catalysts: A catalyst is something that is used to speed up a reaction. It makes the bonds weaker, therefore its easier for a reaction to happen. With weaker bonds there is less energy to make the reaction work. Concentration of Reaction: As the concentration of a reaction increases, then there lots of colliding particles and the collisions being more successful and the rate of reaction increasing.

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11.  ## RATE OF REACTION

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This is because increasing the concentration increases the probability of a collision between reactant particles because there are more of them in the same volume so therefore increases the chance of successful collisions forming more products when reacting with other elements, in this case when Hydrochloric Acid reacts with Calcium Carbonate, Carbon Dioxide is the has given off so the Higher the concentration of Hydrochloric Acid the higher the volume of Carbon Dioxide produced. Increasing the concentration of any of the reactants will increase the frequency of successful collisions as more particles will collide and the concentration of Hydrochloric Acid will increase and therefore increase the speed of products being formed.

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12.  ## Determine the solubility product of calcium hydroxide

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Ksp is also known as the course of the equilibrium constant, and is constant at constant temperature. As predicted in the Le Chatelier's Principle, precipitate of solid Calcium Hydroxide will form when Ca2+ or OH- ions is added into a saturated solution of Calcium Hydroxide. Therefore, from the concentration of the Ca (OH) 2 in the saturated solution, we will be able to determine both the Ca+ and OH- concentration in the saturated solution. OBJECTIVE 1) To determine the solubility product of calcium hydroxide APPARATUS Burette, Pipette, Erlenmeyer flask, Beaker, Retort Stand, Filter paper, Funnel PROCEDURE Solution I : A saturated solution of Calcium Hydroxide in deionized water.

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13.  ## Heat of Neutralisation - I am going to investigate the heat of neutralisation between acids and alkalis.

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The experiments will always be carried out at room temperature so the initial temperature is the same. I will also repeat the experiments to obtain good results, if the results vary in any way I will calculate the average. Apparatus Measuring Cylinders Pipettes Thermometers Polystyrene Cup Safety To ensure the experiments are carried out safely I will always wear a lab coat and goggles. My hair will be tied up. I will make sure my work area is tidy and will observe all other laboratory rules. Method 1. Measure 25cm3 of acid into a polystyrene cup and take temperature. 2.

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14.  ## The effetct of copper nitrate on the germination of mustard seeds.

these copper tolerant grasses have evolved due to selection pressuresbeing placed on the plants, which has inturn led those who are better adapted, copper tollerant, to survive providing them with a selective advantage. Prediction For this reason i predict copper nitrate will inhibit germination and growth of mustard seeds, especially at relativly low concentrations of copper nitrate as copper nitrate is toxic. if some of the mustard seeds do grow, this will only be due to chance or a mutation giving them a selective advantage in the environment.

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15.  ## To determine the concentration of limewater

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Diluting hydrochloric acid: My first task for this experiment is to dilute the hydrochloric acid. To do this I first needed to work out how many moles I wanted for hydrochloric acid. For this part of my calculation I choose to use text book Calculations for chemistry to help me. Page..... Ca(OH) 2 (aq) + HCl (aq) --------> CaCl2 (aq) + 2H2O (l) 1gdm of Ca(OH) 2 Number of moles of limewater Mr of lime water= 40.1 + (16 x 2) + (1 x 2) = 74.1 Mass of lime water=1g Moles of lime water =mass(g)/Mr So 1/74.1=0.13 mol dm-3 Molarities of limewater solution: Morality = no.

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16.  ## Anti-acids

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A catalyst breaks down a substance to provide a larger surface area to speed up the process. The Rate of Reaction The amount of time the reaction occurs. Magnesium + hydrochloric acid --> Magnesium Chloride + Hydrogen This equation gives me two possible methods of recording the rate of reaction: * Recording how fast hydrogen is produced from the reaction. * Or an alternative you can record how long it takes for the magnesium disappears on the reaction. There are three different factors that can influence the rates if reactions * The strength or concentration of the chemicals.

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17.  ## Formula of a hydrated salt

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Mass = 0.79 g RFM = (1 x 2) + 16 = 18 Therefore 0.79 / 18 = 0.043888888889 mol To find the value of (x) in the formula FeSO4.xH2O you need to find the formula ratio. To do this you divide the moles of H2O by the moles of FeSO4. So 0.043888888889 / 0.004673512375 mol = 9.39 (3sf) = 9.4 (2sf) Therefore the ratio I have found is 1:9 for FeSO4:H2O. The 9.4 has to be rounded down because it is not possible to have 0.4 of a molecule, you have to make it an integer so you have a whole number of molecules.

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18.  ## How oil is obtained, used and effects our world.

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This is known as fractional distillation. This shows the different heat at which some of the fractions boil at. As you can see the boiling points range from 20? to 400?. The different boiling points are important because this means that you can separate out the crude oil for the desired separate fraction. Some of the fractions are; Kerosene- a liquid hydrocarbon usually used to power aircraft or for heating. Naphtha- this is used to create a high octane gasoline.

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19.  ## concntraion of calium hydroxide

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Since we are provided with a solution there is no particular danger. * When in contact with skin wash of with soap and water. Apparatus: * 250cm3 volumetric flask * 5cm3 graduated pipette * burette * pipette filler * white tile * clamp and stand * funnel * conical flask 250cm3 * 100cm3 beaker Balanced equation: Ca(OH)2 + 2HCl CaCl2 + 2H2O Dilution: Firstly I will calculate the approximate concentration of the calcium hydroxide in mol dm-3 Moldm-3 = gdm-3/Mr = 1/74.1 = 0.014 (3.d.p) Now I will use the balanced equation to work out the approximate concentration of HCl needed.

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20.  ## Identification of an Organic Unknown.

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Universal indicator is a mixed indicator i.e. it is several indicators with different pH values mixed together. When added to solutions of different pH, different indicators change colour as above. The colour you see is a result of colour mixing. The colour has been linked to a specific pH and a colour chart provided. SAFETY: Follow general safety procedures and be aware that universal indicator can be dangerous so always make reference to the hazcards. 2. Test with Bromine Water EQUIPMENT: Test tube Pipette Bromine water PROCEDURE: Add several drops of bromine water into a test tube which if filled with 1cm� of the unknown substance.

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21.  ## Rate of Reaction Investigation

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These below are the five best dilutions we came up with: Vol of Hydrochloric acid (cm�) Vol of Sodium Thiosulphate Solution (cm�) Vol of Water (cm�) Concentration (g/l) 1 10 50 0 40 2 10 25 25 20 3 5 50 5 40 4 5 25 5 20 5 2.5 12.5 7.5 10 After choosing my best five solutions we started to time each dilution. We repeated the method three times with the same solutions. This made my results more reliable and I was able to attain an average time for each dilution. Before doing my final experiment I tried different solutions to decide which one was the best to use and which was the most reliable every time by looking at the results for my final experiment.

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22.  ## An Investigation of Titration

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The indicator will change colour when neutralisation occurs, also the temperature will stop rising. Choosing an Indicator I will find the best indicators to use in my experiment, the three indicators that I will compare are: Phenol Phtalein Methyl Orange Universal Indicator I will find which indicator is more beneficial for my experiment by filling a test tube with about 1/3 of Sodium Hydroxide and then adding a small amount of an indicator in, the first indicator I used was the Universal Indicator. As I added the hydrochloric acid to the sodium hydroxide it became neutralised and the colours kept changing as the substance changed from acid to alkali, it was very difficult to establish when you have reached neutralization as the colour changes to easily.

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23.  ## How does the concentration of an acid affect the fate of reaction?

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There are four major factors that affect the speed of a reaction; Temperature, Concentration, Catalyst and Pressure/Concentration. In this experiment, the effect that a Concentration has on the speed of a reaction will be tested. This means, however, that the other variables will have to remain unaltered throughout all the tests. If they were to vary, the tests could not be considered reliable. I will make sure the temperature does not vary by checking that the room is at room temperature. I will not use catalysts, and make sure that all equipment is not contaminated by any other chemicals. I will use the same equipment in each experiment to make sure that the pressure/concentration does not vary.

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24. ## Chemistry Concerntration Analysis

This method is extremely precise but is a lot more expensive and a lot harder work. A Colorimeter typically retails at around �800 and they also need to be calibrated and adjusted before the experiment, the colour also need to be measured every few seconds, and the results can only be interpreted in graphs. Collision Theory- What is Reaction Rate? Reaction Rate is defined as how fast a reaction takes place. It is a measure of how fast a Chemical Reaction occurs.

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25.  ## Investigation of aqueous electrolytic cells.For this experiment, we are to test an aqueous solution, choosing from the four selections given: sodium chloride, copper sulfate, copper chloride and hydrogen sulfuric acid.

Hypothesis (including reason): If the voltage increases, the amount of solid discharged from the electrode will increase as well. I predict that the solid discharged from the electrode will increase as the voltage increase in the circuit because as the voltage goes higher, the more energy will be produced and the faster the solid will be discharged from the electrode. And hence, the mass of the electrode will gradually become heavier as the voltage increases. Variables: Independent variable: voltage For the independent variable, it is the voltage, because I have to change it as we finish the experiment every time, meaning the input of the experiment.

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