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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!
Finally, the density of solids of irregular shape can be determined by added the solid to a liquid in a volumetric container, taking note of the change in liquid level. Methods and Materials The measure of density can be determined in each of the three states that an object may exist in -solid, liquid, or gas. In this experiment, the determination of density is applied to regular and irregular solid samples, liquids, and solutions. When measuring the density of regular solids, a simple geometric formula may be used to determine the measurement.
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The metal powder easily forms a compound with the non-metal ion of the compound and more energy is given out. When the total energy given out is more than the energy used, the reaction is exothermic and its product is a very stable compound. For this experiment, the four metal powders given are magnesium, zinc, aluminium and iron. They have to take part in a reaction with copper sulphate which is an aqueous solution and its metal ion is copper.
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- The concentration of the substances which are reacting. - The size of the particles - The temperature - Whether or not a catalyst is present. The first two variables do not affect the Maxwell-Boltzmann Distribution. The way they increase the rate of reaction is by increasing the probability of a collision. If the concentration of a solution is increased then there are more reacting particles in the same volume and so there is a greater chance of them colliding with each other. Similarly, if the reacting particles are bigger, then there is a greater chance they will collide. However, the last two variables do affect the Maxwell-Boltzmann Distribution.
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The molar ratio of acid to alkali is now 1:2, so for every Hydroxide ion released from the Sodium Hydroxide, two Hydrogen ions will be released from the sulphuric Acid, and so only 0.5 mole H2SO4 will be needed to neutralise 1 mole NaOH. For the gas collection experiment, I shall again react firstly a monoprotic acid, then a diprotic acid and compare the amounts of gas collected. My first reaction will be between Hydrochloric Acid (monoprotic) with Magnesium Carbonate.
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Collect hydrogen gas evolved using an inverted measuring cylinder 3) Measure the volume of hydrogen evolved at 40-second intervals Results: Time/s Volume/cm� 0 0.0 40 1.25 80 2.25 120 3.0 160 3.2 200 3.4 240 3.6 280 3.8 320 3.8 Observation: As the calcium reacted with the water, I observed the calcium effervescing, and the calcium moved up and down in the cylinder during the reaction. As the reaction progressed, the piece of calcium gradually dissolved smaller and smaller until it was completely dissolved in the water.
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To investigate the rate of reaction between Sodium Thiosulphate (-Na - _2 S_(2 ) O_3) and Hydrochloric acid (HCl)?
I will be doing this investigation in many different ways such as varying the temperature or the concentration of the hydrochloric acid and also I will use a calorimeter which will give me an accurate reading of how much light is absorbed and when the solution has turned cloudy and no light can transmit through it. This is the word equation for this reaction: Sodium Thiosulphate + Hydrochloric Acid Sulphur Dioxide + Sulphur + Water + Sodium Chloride The reaction can also be expressed as a symbol equation: Na2S20 3 + 2HCl SO2 + S + H20 + 2NaCl Apparatus: 1.
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This statement can be supported by both of Faraday's Laws. Faraday's First Law of electrolysis states that: "The mass of any element deposited during electrolysis is directly proportional to the number of coulombs of electricity passed" Faraday's Second Law of electrolysis states that: "The mass of an element deposited by one Faraday of electricity is equal to the atomic mass in grams of the element divided by the number of electrons required to discharge one ion of the element." Another piece of scientific theory we can use to support our predictions is: At the anode (+): Cu (r)
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Use the same sample and heated up the sample to burn off humus. Sample left to cool down. Burned off the humus of soil in the fume cupboard. Evaporating dish for the soil on the hot plate. Got the temperature for the hot plate and fume cupboard. Balance was used in this experiment for accuracy because the balance gives accurate readings. TASK 3 (D4) Accuracy was assured throughout the experiment by not leaning on the benches so it wouldn't affect the readings on the balance. The measuring equipment was the balance, it was set up before using it, to take readings.
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Therefore we can say that the effective collision frequency also increases and thus increases the rate of reaction. Variables: Independent * The concentrations of hydrochloric acid. * Volume of water * Volume of Hydrochloric acid Dependent * Time taken for the cross to disappear. * Colour change of the sodium Thiosulphate and hydrochloric acid. * Change in temperature after the reaction is over. Constant * Volume of hydrochloric acid used. * Volume of sodium Thiosulphate used. * Concentration of sodium Thiosulphate * Surroundings * Room temperature Molar calculations to calculate the concentration of HCl after diluting it with water: The molar value of HCl in a solution can be calculated for each dilution.
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Overall a rise in temperature helps to form more products. Catalyst: The word catalyst means an added substance, in contact with the reactants, that changes the rate of a reaction without itself being chemically changed. Catalysts increase the rate of a reaction by helping break chemical bonds in reactant molecules and provide a 'different pathway' for the reaction. This effectively means the Activation Energy is reduced, irrespective of whether it's an exothermic or endothermic reaction. Surface area: A solid in a solution can only react when particles collide with its surface.
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This therefore allows them to act as catalysts. As there are more spaces for electrons to be lost and gained the reaction can take place faster and better. The general equation for the experiment is: CATALYST 2H2O2 O2+2H20 From the equation it can be seen that Oxygen is produced in the reaction and this is what is being collected and measured in the gas syringe. Prediction: The transition metal oxides MnO2 (Manganese oxide), ZnO (Zinc Oxide) and CuO (Copper Oxide) will be compared with SiO2 (Silicon Oxide), A12O3 (Aluminium Oxide)
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I completed this experiment to test my method and gather an initial set of set of results. After I successfully completed my preliminary experiment I set out to collect my official set of results. I planned to make this series of tests more accurate so I could therefore collect a more reliable set of data. Method 1. Set up the conical beaker on a laminated cross, and two sets of burettes, one to measure out distilled water, and the other for measuring sodium thiosulphate.
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Apparatus and reagents * Bromine Water * Test tubes/Test tube racks * Acidified Potassium Dichromate (VI) (K2Cr2O7) * 2, 4-Dinitrophenylhydrazine (2, 4-DNP) * 5% Aqueous Sodium hydrogen carbonate (NaHCO3) * Water Cooled condenser * Clamp and stand * 20 ml - 400 ml Beakers * Measuring Cylinder * Bunsen burner * Phosphorous Pentachloride (PCl5) * Ethanoic acid * Iron (III) Chloride (FeCl3) * Sodium metal (Na) * Tollens Reagent * Sulphuric Acid * Jones's reagent (CrO3-H2SO4 in H2O) * Water bath * Bunsen burner/heating Mantle * 1 ml of 0.5 mols hydroxylamine hydrochloride * Sodium Hydroxide (NaOH)
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For my investigation I am going to investigate the reaction rate of sodium thiosulphate and hydrochloric acid. The chemical reaction between sodium thiosulphate and hydrochloric acid is: Sodium + Hydrochloric Sodium + water + sulphur + sulphur Thiosulphate acid chloride dioxide 2HCl(aq) + Na2S2O3(aq) 2NaCl(aq) + SO2(g) + S(s) + H2O(l) When sodium thiosulphate reacts with hydrochloric acid a cloudy precipitate is formed, this is the sulphur held in a suspension of water and sodium chloride. A precipitate is a solid formed from a reaction between two solutions.
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Remove the excess of Iron (Fe) by filtering the mixture into an evaporating dish 6. The light green solution in the evaporating dish is dilute Iron (II) Sulphate (FeSO4) 7. Heat gently by the Bunsen burner and evaporate filtrate (until only one-third left). 8. Let the solution cool down naturally after a few days 9. Filter to obtain crystals and wash with distilled water 10. Press crystals lightly between pieces of filter paper and air-dry or use IR light for 1-2 minute.
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The activation energy is the height of the potential barrier (sometimes called the energy barrier) separating two minima of potential energy (of the reactants and of the products of reaction). This can be interpreted through the diagram to the left: This graph also illustrates what happens to the reactants within the reaction, as you can see from the graph the reactants remain stationary, it then increases as you can see a dramatic rise of the line; though successful collisions only take place where the activation energy is shown, the deterioration of the line shows the reaction is thus coming to an end and there is a lowering of the collision frequency making successful collisions less frequent.
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Experiment on The Use of Analytical Balance in Determining the Water Content of a Given Hydrated Salt
To find the mass of the water, we weighed the hydrated salt and then heat the hydrated salt in order to obtained the mass of the dehydrated salt, then the mass of the hydrated salt minus with the mass of dehydrated salt. To weigh the mass of the salt accurately, we use analytical balance and the two-decimal balance to check the accuracy of the mass obtained. Analytical balance is an instrument used to measure mass to a high degree of precision.
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(Biology - A functional approach - M B V Roberts) Enzymes are organic catalysts which speed up chemical reactions in organisms. There are several reasons why the presence of enzymes is so important, these are; * Without enzymes in cells, all reactions within would be so slow they would practically stop completely. * They not only speed up the metabolic processes they also control them As many as 1000 different reactions take place within an individual cell, a mere 20 micrometres in diameter.
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Results and Calculations: Mass of succinic acid used = 1.1 g Aqueous Layer (0.49 M NaOH used) Ether Layer (0.1231 M NaOH used) Final Burette Reading / cm3 11.4 10.5 7.4 12.8 Initial Burette Reading / cm3 2.9 1.9 2.4 7.4 Result / cm3 8.5 8.6 5.0 5.4 Mean Titre / cm3 8.55 5.2 Table 1 Since succinic acid is a dibasic acid, its reacts with NaOH with the following reaction: 2 NaOH(aq) + H2A(aq) Na2A(aq) + 2 H2O(l) where H2A is succinic acid.
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of the blood. All body fluids have buffers that defend the body against pH changes. A process that affects buffers in the blood is exercise. The muscles require more oxygen (O2) whilst exercising as the metabolism is increased and produce CO2 and H+. This then sets a concentration gradient in opposite direction from the oxygen O2 gradient allowing CO2 and H+ to flow from muscles into the blood. Buffering of haemoglobin then picks up excess hydrogen ions (H+) and CO2.
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We cannot depend on just looking at the result that we got from the experiments to settle the more significant method, so I will work out the %errors for both experiment methods to see by what percentage my results were from the expected result. % error of experiment = difference between result & expected x100 Expected result Method1: (1.8 � 24.3) x 100=7.4% Method2: (5.4 � 24.3) x 100= 22% The percentage errors for both methods are quiet high, so this suggests that maybe both methods were not very significant.
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How long the magnesium piece is left in - Temperature of solution and surroundings I will have to keep these the same so to keep the whole experiment as fair as possible. As any of these variables would have an unwanted affect, e.g. if the surface area was different for each magnesium piece, we would assume that the rate of reaction would occur greater in the magnesium piece with the larger surface area, resulting in the whole experiment becoming inequitable.
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?T will be measured in the following experiments. Chemicals: * Calcium metal * Powdered calcium carbonate * 1 M hydrochloric acid Apparatus: * Electrical balance � 1 * Measuring Cylinder � 1 * Beaker � 1 * Thermometer � 1 * Plastic Cup � 1 Procedures: A. Reaction of Calcium with Dilute Hydrochloric Acid 1. About 1 g of calcium metal is weighed out accurately and the weighing is recorded. 2. Using a measuring cylinder, 100 cm3 of hydrochloric acid is placed in a plastic cup. Stirring carefully with the thermometer, the temperature of the acid is then recorded. 3.
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As you increase the concentration of the acid, there are more acid particles in the same volume. Therefore there is a greater chance of acid particles colliding, and reacting, with particles on the surface area of the magnesium ribbon. Here is an example of how the rate of reaction will increase if the concentration gets higher: With this in mind it is clear to see that as I decrease the concentrate of the acid by adding water to it I will be decreasing the rate of reaction.
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