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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
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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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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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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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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The Effect of Concentration on the Rate of Reaction when you React Hydrochloric Acid with Marble Chips3 star(s)
Collision theory states that the rate of reaction increases depending on how often and how hard the particles collide with each other in order to react. Therefore more collisions increase the rate of reaction because the number of collisions between the reactants increases. So, if there is a greater concentration (more particles between the water molecules) there is a greater chance of collisions. There are other factors that need to be controlled. The temperature can also increase the number of collisions because the particle energy is increased so there is a greater chance of collisions.
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2.2 Modifications: * Lab manual stated that only "plastic" lab ware be used in the experiment, but instead, glass was used during the laboratory experiment and not all plastic. * The sample of magnesium salts were not transferred with washings. 3. Experimental Results: 3.1 Determination of Magnesium Using an EDTA Titration.
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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 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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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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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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I added 2.5 grams of carbon powder and mixed well. 4. I heated the mixture strongly until it turned red. 5. I let the mixture cool. 6. I then separated the copper from the waste by half filling put the copper onto the filter paper to dry it. I measured the test tube with water and poured the mixture into a beaker of cold water. 7. I then left for 2 minutes and then poured off the dirty water.
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Equation Magnesium+ Hydrochloric acid? Magnesium Chloride+ Hydrogen Mg (s) + 2HCl (aq) ? MgCl2 (aq) + H2 (g) I will use this balanced equation to represent the reaction happening and the product being made. The magnesium displaces Hydrogen in the Hydrochloric acid, which produces Magnesium Chloride and Hydrogen. Preliminary Test Trial Table Concentration of 2HCl(M) Trial 1 (s) Trial 2 (s) Trial averages (s) 1.00M 124 132 128 2.00M 33 41 37 I think that if you double concentration e.g. 1.0M to 2.0M, the time for the reaction to finish will decrease heavily, but if you double another concentration you will not see the same multiplication.
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Standard state is the physical state at which an element or a compound exists at standard conditions. Hypothesis: If the temperature of a given substance is known, we may calculate the enthalpy of this substance. Experiment I Part I PLANNING (B) Requirements: - 1 beaker [250 cm3] - 2 test tubes - thermometer - 60 cm -3 of 2 mol dm-3 hydrochloric acid - solid anhydrous sodium carbonate (Na2CO3) [3.75 g] - balance Procedure: We were provided with 2 mol dm-3 hydrochloric acid, solid sodium hydrogencarbonate and solid anhydrous sodium carbonate. 1. One person in each pair measured 30 cm3 of approximately of 2 mol dm-3 hydrochloric acid into the beaker.
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which dissociates in water will lower the freezing point more than a one molal solution of a non-electrolyte (sucrose). The freezing point depression method is used in the preparation of isotonic solutions and also in the determination of molecular weights. Pre Lab Questions 1. What is a colligative property? Colligative properties are the properties of dilute solutions of non-volatile solutes whose values depend only on the concentration of solute particles, not on the type of particles present . 2. What are the molecular weights of: (a) Sucrose 342.3 g/mol (b) Sodium chloride 58.4 g/mol 3. Explain what happens, on a molecular/ionic level, to the following when dissolved in water: (a)
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Heat with water bath in case if necessary. Outcome- A colour change to orange/ yellow indicates that presence of a carbonyl group, which will be aldehyde or a ketone. No colour changes indicate that is an alcohol, carboxylic acid, ester or phenol. Explanation - This is the equation for the reaction of ethanol with 2, 4- dinitrophenylhydrazine is: Equipment, Test tube, Pipette, 2, 4- DNPH solution, 1cm3 of ethanol. 4. Test for an aldehyde Procedure - Put about 1cm3 of 0.05m silver nitrate solution into a test tube and add 3 or 4 drops of sodium hydroxide solution.
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Vitamin C in food can be destroyed by cooking, leaching out from fruits and vegetable during washing, and being oxidized when expose to the air. Thus, food that rich in vitamin C needs to be stored and prepared well. PROCEDURE 1. Standardization of 0.001M 2, 6-dichlorophenolindophenol solution. 25.00mL aliquot of ascorbic acid solution was pipette into a 100mL conical flask. 0.001M 2, 6-dichlorophenolindophenol solution is titrated until a faint colour persisted for at least 15 seconds. The molarity of the dye solution is calculated by the result obtained.
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Put a small amount of aluminium oxide about half way along the boiling tube. Complete the set up of the apparatus as shown in the diagram above. Light the Bunsen burner, adjust it to a blue flame and heat the aluminium oxide. (Make sure the test tube is filled with water when you start to collect the gas produced.) As the aluminium oxide gets hot the heat reaches the ethanol at the end of the tube. The ethanol then changes to vapour, passes over the hot aluminium oxide and is dehydrated to produce ethene gas.
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Also I predict that as the volume of water is increased the amount of sugar that I will able to be dissolve into the water, will also increase because there are more spaces between the molecules of water, because there are more water molecules, for the sugar molecules to fit in between. Diagram Method To set up my experiment first I will set up my scales I will then measure how much the beaker I am using to hold the water weighs, I will then zero the scales and add the water to the desired volume (weight).
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Determining the Identity of an Unknown Contaminant in a Solution through the Use of a Designed Solubility Chart
The spot plate was taken and all the spots were filled with 2 drops of Aluminum ion solution. 3. Even though only seven spots were required, extra was filled for inconclusive results. 4. Then all the anions were tested with one drop of each Acetate, Bromide, Carbonate, Chloride, Hydroxide, Phosphate and Sulfate ions were dropped in each of the spot wells. 5. The results were recorded in Data Table 1.0 with an "I" for insoluble and "S" for soluble.
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The equation below shows what happens when soap is added to water. Again, not all the ions present in the above equation actually play a part in the reaction, the ions that do are: It is important to make sure that all measurements and readings are precise, e.g. the weighing of the sodium carbonate and the cleanliness of the apparatus. Many of these key factors are variables. By using these variable one can ascertain different results. The results of the experiment will be affected by the changing the amount of sodium carbonate or the amount and/or source of the water will affect the results of the experiment, and most of all the cleanliness of the apparatus.
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This is because, as you can see on the diagram at the top right, the outer electron is closer to the nucleus than the other two metals, and so the force holding it is quite large. Sodium, atomic number 11, will be the second most reactive, as its atoms are larger. And finally, Potassium, atomic number 19, will be the most reactive and produce the most energy because its outer electrons are least strongly held by the positive nucleus. Variables Independent - Group one metal (lithium, sodium and potassium).
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* Carbon dioxide - is present if when bubbled through lime water- it goes cloudy. During the experiment I will wear safety goggles, gloves and a laboratory coat throughout the whole experiment as some substances may cause irritant to the skin and be dangerous if in contact with skin and eyes. I will use 8 tests in total to identify the identity of the unknown organic compound. Alkenes Alkenes are unsaturated hydrocarbons and contain at least one double C=C bond. Unsaturated means that additional reactions can occur to break the C=C bond. They have the general formula of CnH2n with the structural formula of: C=C They have a planar shape with bond angles of 120.
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This will then mean all the concentrations needed for the calculations are in the same units:- 1 g/dm� mol/dm�. To work out the concentration of Ca(OH) 2, I will use: Concentration (mol) = Mass(g) / Molecular mass of Ca(OH) 2 = 1g / (40 + (16X2) + (1X2)) = 1/74 = 0.01 mol/dm� of Ca(OH)2 This means we have a 2.00 mol/dm� solution of hydrochloric acid and a 0.01 mol/dm� solution of calcium hydroxide. Dilution Factor I will use 25cm� of limewater solution to give me a reasonable result, which I can accurately measure out using a 25cm� pipette.
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