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GCSE: Aqueous Chemistry
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The rates of aqueous reactions
- 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 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 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 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.
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
The two most important equations to learn are:
moles = mass / Mr and moles = volume x concentration
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 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 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 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 Anything that is dissolved in an aqueous solution will have the state symbols (aq). For Na+(aq)
- 2 If your reaction is dissolved in water, then water will have the state symbol (l), for “liquid”.
- 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 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 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
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 chlorid5 star(s)
?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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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.5 star(s)
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
- Word count: 1805
Biology Practical Investigation to find the lowest concentration of Copper Sulphate solution that will denature egg albumen.5 star(s)
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.
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You can now read off the volume of base you've added. From this you can workout the concentration of the acid. As I know all the concentrations of the acids and alkalis given I can do another experiment, which is to measure the heat of neutralisation otherwise known as the enthalpy of neutralisation. Enthalpy is the measure of energy usually heat energy that a substance has. You can't measure enthalpy directly, but you can measure the change in enthalpy when a reaction happens.
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Investigation into the effect of acid/alkali strength on the heat change when acids and alkalis are mixed5 star(s)
When the acid and alkali of the same volume are mixed, this will cause the process of neutralisation to occur. Neutralisation is the reaction between an acid and a base. It is the formation of a bond between H+(aq) from the acid and OH-(aq) from the base. These are known as the reacting ions. This is because in the solution the ions are dissociated and thus independent. H+(aq) + OH- (aq) H2O (l) As this is a bond forming process it is known that it will liberate energy, thus all reactions between acids and bases are exothermic.
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Conductivity Lab. Purpose: To determine which substances are ionic and which are molecular based on their ability to conduct electricity4 star(s)
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.
- Word count: 1012
Back Titration Lab Report. In my experiment, I hoped to find the amount of calcium carbonate in some mineral limestone using the back titration method4 star(s)
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.
- Word count: 737
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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In any state, the particles present will have a very wide range of energies. For gases, this can be shown on a graph called the Maxwell-Boltzmann Distribution which is a plot of the number of particles having a particular energy. This graph below only applies to gases, but the conclusions that we can draw from it can also be applied to reactions involving the liquids. The area under the curve is a measure of the total number of particles present.
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Pour 5cm cm� of special indicator containing starch into the 10 cm� measuring cylinder. 7. Pour all the liquids into the 100 cm� beaker and start the stop clock. 8. Stir the solution until it turns a blue/black colour and the cross below is not visible. 9. Record the time it took for the solution to change colour. 10. Wash your apparatus. 11. Pour 30 cm� of potassium iodide and 40 cm� of sulphuric acid into the 100 cm� measuring cylinder and also 5 cm� special of indicator.
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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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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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Investigate the effect of changing the concentration of sodium hydroxide (alkali) on the volume of hydrochloric acid needed to neutralize a fixed volume of alkali by measuring the temperature and noting colour changes of the solution mixture.4 star(s)
Those with a pH of 8-14 are alkaline. PH 7 represents a neutral solution. Indicators are dyes which change colour to indicate weather a substance is acidic, alkaline or neutral. Some indicators such as the universal indicator are made of mixtures of dyes. Acidic substances turn the indicator red and those that are alkaline change the indicators colour to blue. Substances that are neutral change the indicator to green. In this experiment the most suitable indicator that should be used would be the universal indicator. This is because at the point of neutralization the indicator will give a specific colour change to show that the mixture has been neutralized.
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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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Within each hair strand the keratin chains are also linked with ionic, salt and hydrogen bonding. Hydrogen bonding occurs from the attraction between the electronegative oxygen atoms on the CO groups and the electropositive H atoms on either the OH or NH groups. Although they are individually weaker than disulphide bonds, hydrogen bonds are in much higher proportions to the disulphide bonds making them important in maintaining the tertiary structure of the protein. Hair is very resilient and has elastic properties.
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The longer you leave the heater on the hotter the water will get. I don't want to do number 2 because variable power supplies are not precise enough for the level I want to investigate this to and so therefore the test could be unfair. So I have chosen number 1 because I can use scales with the degree of accuracy of 1/100th cm3. Varying the mass of the water will give me and array of varied results and I can be accurate in my method.
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I intend to use five different concentrations of hydrochloric acid and they will be: > 1 m > 0.8 m > 0.6 m > 0.4 m > 0.2 m DEPENDANT VARIABLE: The factor I will measure during the experiment, will the temperature change in the solution of the alkali and acid? I will do this by: Measuring the initial temperature of the solution Adding the alkali - sodium hydroxide Measure the temperature after 1 minute preferably after the reaction has taken place.
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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.4 star(s)
* 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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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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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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To see how the concentration of acid, reacting with potassium carbonate, affects the rate of reaction4 star(s)
This is because as the reaction starts it is very quick and as the chemicals continue to react the reaction produces less CO2 per 10 seconds so it slows down gradually resulting in a curve, This is because after some time there are fewer acid and potassium carbonate particles so the reaction slows down. I predict that the reaction will go slower when the concentration of the acid decreases. This is because the rate of reaction increases with the concentration.
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be neutral; the baking soda solutions will be acidic; the "green" cleaner will be basic; the household cleaner will be acidic; the Lemon Juice will be acidic. Materials: For this lab we need pH paper, a spot plate, water (distilled, if available), and substances with varying pH. Safety: In this lab we must were goggles and aprons to avoid skin contact with all chemicals that are going to be used in this experiment.
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A catalyst could also not be used as these were forbidden in school. Strategy Deciding which reactants to use Experiment One For the first experiment I chose to use calcium carbonate chips and hydrochloric acid. I used 50 ml of hydrochloric acid and 3 calcium carbonate chips and recorded how long it took for the reaction to take place. This took 23 minutes and 43 seconds. Experiment Two For the second experiment I made a sodium thiosulphate solution, by placing sodium thiosulphate crystals into a beaker with a measured amount of water in it.
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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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What are the possible applications of the heat of neutralisation? 4) What are the possible ways to reduce the heat of neutralization in case a patient taking antacids is sensitive to heat? 5) Does the heat of neutralisation depend on the type of Acid Base combination? 6) Does the heat of neutralisation depend on the temperature of the surroundings? 7) How would the physical states of the reactants affect the heat of neutralisation? 8) How would miscible impurities affect the heat of neutralisation?
- Word count: 968