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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!
Find out the accurate concentration of an aid solution thought to have a concentration of between 0.05-0.15 mol dm3 by using the titration method...
Remember that alkalis can be just as corrosive as acids so take care. 2. Use a pipette and pipette filler to transfer 25.0 cm3 of the acid sample to a 250cm3 conical flask. Add 4 drops of methyl orange indicator. 3. Make 250cm3 0.1 mol dm3 sodium carbonate solution. To do this I will need to measure out 2.6g of powdered Na2CO3. This quantity has been calculated by the following method: 1 mol Na2CO3 = 106g, (Na= 2 x 23 = 46) + (C=12) + (o=16 x 3 = 48) = 106g. I only require a 0.1 mol solution so 106/10 = 10.6g.
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So that is why I am testing these metals, so that the blade will last for a long time and so that it would not deteriorate while the person is skating. Apparatus These pieces of equipment will be needed to carry out my experiment, to a good standard: * Test tubes (x15) * Test tube rack * Acid (hydrochloric acid) * Alkaline (sodium hydroxide) * Water * Different metals (zinc, aluminium, copper, iron, magnesium) * Pipette * Measuring cylinder Safety * Make sure that when dealing with the acid, handle it with care.
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Then place the loop in the hydrochloric acid and then place in the flame. * Place the loop in the salt and then place it in the flame. * Record the colour of the flame * Repeat the test for the other four salts and record what colour the flame becomes. * In between each test sterilise the loop so the test will not get contaminated. Safety * When suing the Bunsen burner make sure there that there is nothing close to your working area which is flammable. * Wear gloves and goggles to protect your eyes and hands.
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The aim of this investigation is to see how fast a reaction occurs between sodiumthiosulphate and hydrochloric acid when we change important factors such as concentration of the solution
The other three variables will be kept the same to ensure a fair test. Concentration of the solution affects the speed of a reaction by the way the particles are spread out. If there is a higher concentration of acid, the particles will be densely packed resulting in a chance of a collision hence a faster reaction. If there is more distilled water the acid particles are more spread out lowering the chance of collision, therefore a slower reaction. The formula for this reaction is shown below. Na2S2O3+2HCI~NaCL+SO2+S+H2O Equipment * BEAKER FOR THIOSULPHATE * TUBE FOR ACID * PAPER WITH CROSS ON IT * STOPWATCH * REACTION VESSEL Method As I have chosen to change the concentration of the solution I will need to change the levels of both distilled water and thiosulphate.
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Determining the concentration of a limewater solution. This procedure will require a titration of an unknown concentration of limewater using a precisely known concentration of hydrochloric acid
Method: Firstly add 25.0ml of the sample limewater to a conical flask. Place the flask on a white tile, to make the change in colour more noticeable. Add 5 drops of indicator to the flask any appropriate indicator could be used in this titration such as ?-naphtholbenzein or thymol blue, I am going to use phenolphthalein . This will be the indicator to tell me when the titration is complete. Fill the burette with the dilute HCl. I will talk about the dilution later. Firstly carry out a rough titration and record the hydrochloric acid level at which the indicator turns colourless.
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Chemistry - What is the atomic mass of lithium? Method one: The first method involves reacting a known mass of lithium with a known volume of distilled wa
1. This was my rough titration, I did this to find, where the titration became neutral. 2. This titrated was very close but I think went too far. 3+4 where very close titrations which is really what I expected. It is easy to see from my table tat the results I have recorded do not following 3 significant figures like the rest of my results. I have done this for a deliberate reason. This section is so crucial that I think it is reasonable to get the highest degree of accuracy I can find.
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CH3COOH CH3COO- + H+ Aim: To find out the concentration of different vinegars by titration. Prediction: Equation of neutralization: REACTANTS PRODUCTS Acid + Base � Salt + Water CH3COOH (aq) + NaOH (aq) � CH3COONa (aq) + H2O (l) Acid and base are electrolytes, so when they dissolve in water they dissociate and produce ions. The acid produces H+ ion and the alkali produces OH- ion. Equation: H+ (aq) + OH- (aq) � H2O (l) Ethanoic acid is a weak acid so it has less H+ ions as less of the acid molecules disassociate to form ions.
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To distinguish between the 5 aqueous solutions there are a number of tests and experiments that can be carried out. The tests are best explained as a method and a detailed analysis of the reactions is added further on
The one goes milky (white precipitate) from colourless is the Calcium hydroxide so this can be eliminated. Label it. 2) The remaining 4 samples are still useable for the next test so, add 10cm3 of silver nitrate to all 4 of the solutions. One solution should give a cream precipitate (Bromide) and another should give a white precipitate (Chloride). 3) Separate the two samples and to these, add excess ammonia. The one which dissolves is silver chloride. Potassium Bromide and Sodium Chloride have now been eliminated. Label them. 4) The remaining solutions should be disgarded (the ones with silver nitrate in)
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Sodium sulphate * Tap water HEALTH AND SAFETY - Hydrochloric acid is corrosive and may cause burns must be handled with care. - Nitric acid is corrosive and can cause severe burns should be handled with care when in use - Barium chloride is toxic should not be inhaled in large quantity - Silver nitrate causes burns so should be handles with care. - Potassium is highly flammable must not be used near flames and handled with care. - Iron is irritant and harmful to eyes and skin should be handled with care - Sodium is highly flammable and corrosive, should be handled with care and avoid using near flames.
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However, if there are small particles, and small particles of another compound, then the reaction rate would be slower, because the particles wouldn't collide as easily as they would with particles of a bigger size. The third factor that affects collisions is the temperature. If there is a higher temperature, then the particles are able to move freer and faster, than they would if the temperature was lower. This means that the reaction rate would be faster, because the collisions of the particles are more frequent.
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The purpose of this experiment is to oxide ethanol a primary alcohol and then to test the product to determine whether it has been oxidised to ethanal an aldehyde: CH3CH2OH + [O] → CH3CHO + H2O
This meant that there was an exothermic reaction between the acidified sodium dichromate and ethanol that caused it to continue boiling on its own. After the solution had been bubbling for a while a colourless distillate began to distil over the distillation funnel and was collected into a boiling tube which was held in a beaker with an ice and water mixture in so if the ethanal was produced, it didn't just evaporate away because of its low boiling point.
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My prediction is the higher the concentration of HCL the quicker the Sodiumthiosulphate will react with it.I think this because there are more particles colliding with each other
Measuring cylinder Fair test: To make the experiment fair we repeated it two times on the same day so that the room temperature was the same throughout the test. We cleaned the equipment after the experiment so they were clean and did not have any of the mixed solution left in it. Method: Our method was- * Collect apparatus * Set up apparatus * Pour 25 ml into beaker of HCL * Pour 25 ml Sodiumthiosulphate * Set timer * Start the timer when solutions are together * Record time * Repeat using 1mol * Repeat using 0.5mol * Repeat using 0.25mol * Repeat using 0.125mol * Repeat and record time Results: Test 1 Hcl (MOL)
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To run the synthesis of calcium oxalate via the precipitate from solution containing calcium ion and oxalate ion.2. To do a thermo gravimetric analysis on calcium oxalate.3. Understand and practice the method of homogeneous precipitation
Synthesis of calcium oxalate was done by the reaction between calcium ions and oxalate ion: Ca2+(aq) + C2O42-(aq) CaC2O4(s) In which prepared via precipitation from solution at about pH 5 called homogeneous precipitation. Since calcium oxalate is an oxalic acid, it dissolve in acidic solution, to make the calcium oxalate form precipitate, the solution was adjust to more basic by addition of ammonia, but this is not done by adding the ammonia solution directly into the solution. Conversely, make the ammonia forms slowly within the solution through the reaction of hydrolysis of urea: (H2N)2C=O + H2O 2NH3 + CO2 Urea is a suitable compound in this reaction because it can decomposed easily to form ammonia.During the
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+ 2NaOH(aq.) � Na2SO4(aq) + 2H2O(l) Below is the titration curve of sodium hydroxide and Sulphuric acid: Phenol red, having a pH transitional range of 6.8 to 8.4 is used, because the final pH of the reaction lies between its range. Diagram of the titration This kind of titration is known as back titration, as the excess reactant is titrated in order to find out the number of moles of sodium hydroxide used in hydrolysis. Using the equation no. of moles = molarity * volume used (dm3), the number of moles of Sulphuric acid used can be found out and so does that of sodium hydroxide.
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I have to plan an experiment to find the solubility of calcium hydroxide, Ca(OH)2, in water. I have to make up a solution of calcium hydroxide and carry out a titration using hydrochloric acid solution of the chosen concentration
the experiment I will be using 25cm3 of the solution from the volumetric flask, so the mass of the calcium hydroxide in one titration will be: 0.375 / 10 = 0.0375g Therefore the number of moles of calcium hydroxide: 0.0375 / 74 = 0.0005 moles Ca(OH)2(aq) + 2HCl --> CaCl2(aq) + 2H20(l) As seen from the equation the ratio of hydrochloric acid to calcium hydroxide is 2:1, therefore we need twice as much hydrochloric acid. The number of moles of hydrochloric acid required to react with 0.0005 moles of calcium hydroxide will be: 0.0005 x 2 = 0.001 moles Ideally
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A Thermometer to measure the temperature of the solution to make it a fair test. A Stopwatch to time the experiment to see how long the reaction takes. 2 moler Hydrochloric Acid, this will be the reactant. Water will be used to dilute the acid. Magnesium Strip will be put in the acid to see how long it takes to react. METHOD: To carry out this experiment I will use the equipment listed above. Firstly I will use a measuring cylinder to measure the acid and another to measure the water to dilute it with.
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To use the term "neutral point" in this context would be misleading. The equivalence point is often determined by visual indicators are available for titration based on acid-base neutralization, complexation, redox reactions and is determined by some type of indicator that is also present in the solution. For acid-base titration, indicators are available that change color when the pH changes. When all of the analyte is neutralized, further addition of the titrant causes the pH of the solution to change causing the color of the indicator to change.
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* The indicator solution, will change colour from blue to green and then to yellow when in excess, this is known as the endpoint. Although it will be green at the equivalence point. * The calibration mark on the acid micropipette is read off and will be recorded in a table. * This procedure will then be repeated three times, in which the readings should be with in 0.02cm3 of each other, so that an average can be calculated. * Once this is complete, the base, sodium hydroxide will be titrated against the ethanoic acid.
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at regular intervals is plotted along one axis and the number of moles of added acid or base at these intervals along the other axis; such a plot is called a titration curve and is usually sigmoid (S-shaped), with the inflection point, where the curve changes direction, corresponding to the equivalence point. From the pH at the equivalence point, the dissociation constant of the acidic or basic group can be determined (see chemical equilibrium). If a compound contains several different acidic or basic groups, the titration curve will show several sigmoid-shaped curves like steps and the dissociation constant of each group can be obtained from the pH at its corresponding equivalence point.
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Indicators or are weak acids or bases that undergo dissociation in a known pH range. It is in this range that the acid (or base) is a different color from its conjugate base (or acid). There are many different kinds of chemical indicators. The classic example is litmus paper. I will use methyl orange for my experiment because it is the most suitable indicator for a weak alkali and strong acid. This indicator will change color from red (at pH 3.1) to orange-yellow (at pH 4.4) when acid is neutralised. Equation of the Titration I will be doing: Acid + Base Salt + Water Sodium carbonate + sulphuric acid ===> sodium sulphate + water + carbon dioxide Na2CO3(aq)
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Investigating the Effects of Increasing Copper Sulphate Solution Concentrations on the Germination of Cress Seeds
I will also prepare one of purely water, so that I can compare with a batch that had no copper sulphate whatsoever in the solution. I will use pure distilled water to add to each solution. I am using distilled water in the solution because it means I can control the levels of other macronutrients and micronutrients available. If I remove the other nutrients, it will mean that it is only the levels of copper sulphate available that is changing.
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The aim of the investigation is to find out what speeds up or slows down the effects of rusting in iron. To do this I will place Iron in different solutions
Equipment Equipment list: * * Test tube (x5) * Nail (x5) * Magnesium * Water * Salt * 2 bungs * Drying agent * Oil * Kettle * Test tube rack Method: i. Boil the kettle (for the one that uses boiling water) ii. Put one test tube into each of the sections in the test tube rack. iii. Drop one nail into each of the test tubes (remembering that one of them must be wrapped in magnesium first. iv. Add the liquid/powder into the correct test tubes making sure that they are done at the same time using the same amount of liquid/powder (80mm?).
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Recrystallization - choose the most appropriate solvent to obtain a successful recrystallization of benzoic acid.
Decolorizing charcoal is added if colored impurities are present. 6. The hot solution is filtered through the flute filter paper into the heated flask. The original flask and the filter paper are rinsed with little hot water. 7. The solution of benzoic acid is removed from the hot plate and allows it to cool, undisturbed at room temperature. 8. After several minutes, some crystal is growing in the solution. After 15 minutes, the flask is cooled in the ice bath.
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Aim/Objective: To find out the dissolved oxygen content (in mg dm-3) in a water sample by titration of iodine against thiosulphate solution.
= 24.7mgdm-3 5) Discussion: A number of precautions needed to be carried out in the experiment. First of all, the volumetric flask should be filled completely with the water sample, because if some spaces were spared in the flask, oxygen in the spaces may dissolve into the solution, increasing the calculated dissolved oxygen content in the sample. In contrast, some of the dissolved oxygen in the sample may evaporate into the spaces, giving smaller dissolved oxygen content. Also, when filling any solution into the volumetric flask, no air bubbles could be trapped. This is because any air bubbles may increase the oxygen content in the volumetric flask, increasing the dissolved oxygen content in the sample.
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Determining the atomic mass of lithium from method one. After setting up my apparatus, I went on to measure my Lithium metal
This is to reduce the risk of contamination. Determining the atomic mass of lithium from method one. After setting up my apparatus, I went on to measure my Lithium metal which was stored in paraffin because of it reactive nature. I dried a particle before weighting it. This is because the paraffin can affect the mass and may even affect its reaction. After ensuring the Lithium metal was totally dry from the paraffin; I took the mass of the weighting boat alone which was 1.055g, I then took the mass of the weighting boat with lithium metal 1.148g This gives the mass of the lithium to be 0.093g
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