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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!
10) Work out the mean result. 11) Repeat steps (1) - (9) but change your material each time. Preliminary Results (1) All results to 2 decimal places (2.d.p) In this preliminary, I used three different balls which two of them were roughly the same size and weight except for the lead, even though it was about the same size, it was about 1000g heaver than the brass and copper. I dropped it in the same viscous liquid to test how long it took for them to drop to the bottom of the measuring cylinder. It has shown that on average the lead ball dropped to the bottom the fastest with the average speed of 48.64 seconds.
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Rub sand paper on both the electrodes, wash with de-ionised water, ethanol and finally propane and then let them dry. 2. Then weigh the electrodes, handling them carefully to prevent them from becoming greasy. Record your readings. 3. Take copper (II) sulphate solution in a beaker and place the electrodes in it. 4. Set up the following circuit: 5. Switch the circuit on and quickly adjust the variable resistor on the power pack so that the ammeter displays a reading of 0.10 amp. 6. Allow the current to flow for a measured period of time. Maintain the constant current. 7.
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similar to a battery and produces electricity while the reactants are supplied continuously from an external source. Fuel is fed continuously to the anode while the cathode is being feeding the oxidant. The electrolyte layer that acts as a doorway allows ions to pass through however no electrons because they are being forced into the external circuit creating a chemical reaction. One important factor about the hydrogen fuel cells is that it will continue to supply fuel until the fuel (hydrogen being an unlimited resource) has finished. Hydrogen fuel cells do not require electrical recharging and can generate power almost indefinitely as well.
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Experimental Results: 3.1 Data Table CLASS DATA Raw Data - Concentration Data Reaction Time Avg time (s) Reaction mL H2O2 ml I- Run A Run B Run C 1 5 5 839 1300 1245 1128 2 7.5 5 379 594 796 590 3 10 5 632 447 764 614 4 12.5
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Barium Chloride * Silver Nitrate * Potassium Thiocyanate * Dilute Nitric Acid * Iron (II) Iron (II) Sulfate Sodium Hydroxide Color change to mossy green. Precipitate is heavy and gathers at the bottom. Barium Chloride * Silver Nitrate * Potassium Thiocyanate * Dilute Nitric Acid * Iron (III) Iron (III) Chloride Sodium Hydroxide Color change to orange. Precipitate is formed. Barium Chloride * Silver Nitrate * Dilute Nitric Acid * Potassium Thiocyanate * Iron (III) Iron (III) Chloride Potassium Thiocyanate Color change to bloody red.
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Record your result in Table 2. Note that mixing of coloured solutions can give another coloured solution. Furthermore, apart from the vanadium ions, other coloured products may be also be formed. (If you suspect iodine to be produced, test by adding about 3cm3 of 0.2M sodium thiosulphate solution into test tube.) 6. Data Treatment No. of mole of ammonium metavanadate = 2.5x10-3 mol Mass of ammonium metavandate = 2.5x10-3x (14+4+50.9+16x3) = 0.29225g Mass of ammonium metavandate used = 0.29g Table 1 Chemical mixed Observation NH4VO3+ H2SO4 The color of mixture turns to pale yellow.
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Competition reactions in aqueous solutions * In displacement reaction, a more reactive metal will displace a less reactive metal from a solution of its salt. c. Identifying metal ions * When an alkali dissolves in water, it produces hydroxide ions. * Most metal hydroxides are insoluble.. * If hydroxide ions from a solution of an alkali are added to a solution of an metal salt, an insoluble often colored metal hydroxide is precipitated from solution. * In some cases the precipitate dissolves in excess hydroxide, owing to the amphoteric nature of the metal hydroxide.
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tensile strength - required for large bridges Manufacture of Na2CO3 - the Solvay process Used to manufacture soaps, detergents, dyes, drugs Na2CO3 = CaCO3 + NaCl + CO2 + NH3 in a Solvay tower, the centre of reactions CO2 and NH3 are recycled continuously Indirect uses of limestone Lime manufacture When CaCO3 is heated, it breaks up reversibly to form CaO and CO2. CaCO3 - CaO + CO2 .Thus reaction can go in either direction, depending on the temp and the pressure and takes place in a lime kiln.
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Precipitation. The purpose of this experiment is to become familiar with precipitation reactions. According to the textbook, precipitation is the process where a chemical reaction leads to the formation of a solid, which is called a precipitate.
Methods and Materials This experiment required the mixture of several different substances, followed by observation of the results. To perform these tests, a microtiter plate was used to contain the individual drops of substances. The substances provided included the following solutes: sulfuric acid, hydrochloric acid, silver nitrate, sodium carbonate, sodium chloride, potassium chromate, lead acetate, sodium sulfate, and barium chloride. Using pipets, these solutes were carefully mixed on the microtiter plate, which was used as a reaction chamber. Carefully, the reagents were dispersed and mixed, while the reactions observed and recorded. To discover the results of the reactions, it was necessary to use solubility rules to predict the reactions.
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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 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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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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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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(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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?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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I filled the burette to about 1 cm above the 0 cm3 mark, and then ran a little through the tap until the level was on 0. If the level fell below this, I recorded the precise volume (to the nearest 0.05 cm3) 7. I titrated slowly with the sodium hydroxide solution, with constant swirling and added 2-3 cm3 at a time. 8. When the liquid began to have swirls of yellow, I added the acid one drop at a time.
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Measure a small amount of sodium chloride in a test tube add a few drops of concentrated sulphuric acid. Do this in the fume cupboard and make sure you are wearing gloves. 2. Note the effervescence (bubbling) as hydrogen is produced. Blow across the mouth of the test tube and note the misty fumes. 3. Test the gas with moist universal indicator paper. Then dip a dry, clean glass rod into concentrated ammonia solution in the fume cupboard and hold the rod over the mouth of the test tube. Note the white smoke. 4. Put the test tubes in a rack and leave in the fume cupboard.
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Preparation Before the titration can take place, the correct concentration of HCl must be found and prepared. Using certain equations, this can be achieved. Reaction Ca(OH)2(aq) + 2HCl(aq) --> CaCl2(aq) + 2H2O(l) 1 mole of Calcium Hydroxide reacts with 1 mole of Hydrochloric Acid. Concentration of Limewater (Ca(OH)2(aq)): Conc. approx = 1g dm-3 Mr(Ca(OH)2) = 40 + 2(16 + 1) = 74 Moles = Mass / Mr Moles = 1 / 74 Conc. approx = 1/74 moldm-3 = 0.0135 moldm-3 Concentration of Hydrochloric Acid (HCl(aq)): Original Conc.
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PLANNING (B) Requirements: - 3 aspirin tablets (Acidium acetylsalicylium 500 mg) - pipette (25 cm3) - safety filler - burette (25 cm3) and stand - small beaker - 2 standard flasks (250 cm3) - 3 conical flasks (250 cm3) - small funnel - lime water - Bunsen burner - Tripod and gauze - 1.0 mol dm-3 sodium hydroxide solution (30 cm3) - 0.10 mol dm-3 hydrochloric acid (150 cm3) - phenolphthalein as indicator - eye protection Method: A known amount of standard sodium hydroxide solution is used in excess to hydrolyse a known mass of aspirin tablets.
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Hypothesis: If the temperature of a given substance is known, we may calculate the enthalpy of this substance. Prediction: The results of this experiment will probably be similar for sets of different acids and hydroxides. Different concentrations of the same acid will not influence the enthalpy of neutralisation. Assumptions: The density of acids is equal to the density of water and amounts to 1.00 g cm-3 Key variables: m - mass of a substance in grams s - specific heat capacity in J g-1 K-1 ?T - the amount by which the temperature is increased in K PLANNING (B)
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High Low Chemical reactions only occur when reacting particles collide with each other with sufficient energy to react. Before two particles can react, they must have the minimum collision energy required for a reaction to take place. The minimum collision energy required for any given reaction is called its activation energy. The faster a particle is moving the more kinetic energy it has and so the more collisions will take place therefore speeding up the reaction producing the products faster.
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