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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!
==>==> When Sodium Thiosulphate reacts with an acid, a yellow precipitate of sulphur is formed. Diagram: As you can see, the higher the concentration, the more collisions between particles will happen Variables: During the experiment I will keep the amount of Hydrochloric Acid the same and the total volume will always add up to 60cm3 to make it a fair test. I will change the amount of Sodium Thiosulphate from 50cm3 and decrease each time by 5cm3 and increase the amount of water to investigate whether concentration affects reaction time.
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There is one type of quantitative analysis used which is Titration. The experiment which I am undertaking is finding out the volume of HCL needed to neutralise (1 mol dm -3) NaOH. I will then make a brief record on the results.
* I used a pipette to measure out 25 cm3 of sodium hydroxide solution (1 mol dm-3) using a graduated pipette (with pipette filter) into a 250cm conical flask that had been rinsed out with distilled water. * I added 3-4 drops of Phenolphalein indicator. * I held the burette in a clamp and stand, I washed a burette twice with a few cm of the hydrochloric acid whose concentration had to be found. * I cautiously poured the (1 mol dm-3) of hydrochloric acid being cautious by bringing the burette down to my eye level and used a filter funnel lifted slightly from the top of the burette to allow air to escape.
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Then put on your safety goggles. We set up the equipment. Then added the amount of thio, hydro and water. We stirred it 10times. Then started the timer. We waited till the solution was cloudy. To make sure it was the same each time we put a black cross underneath it and recorded when you couldn't see the black cross. We carried out all the different volumes of solutions then recorded it into out tables. The different volumes depended on which test we were doing.
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A neutralised solution has a pH of 7. In this experiment I am going to measure the pH of the acidic solution when certain amounts of lime are added, lime is a basic substance. When a base neutralizes an acid, Acid + Base Salt + Water According to this theory, I expect that the vinegar, which is an acid in the experiment, will be gradually neutralized by a base. When it is being neutralized, the pH will be higher, so I expect the color will change towards the neutral color of pH 7, which is green, then the pH will be higher again and gradually turns to purple, which presents a high pH.
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out 4 cm cubed of milk and put it in a test tube Repeat this once more putting the milk in another test tube Measure out 4 cm cubed of rennet and put this in a different test tube again Repeat this one more putting the rennet in another test tube There should still be 2 clean test tubes Heat the milk in one test
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We found that universal indicator gave us the most varied results and was the closest to the neutralisation point. Prediction I predict that the higher the concentration of the acid the more alkali will be needed to neutralise the acid. Hypothesis an equal amount of the same strength acid and alkali will neutralise each other, so if there is 100ml of 1 mole acid and 100ml of 1 mole alkali mixed together the solution would become neutral. Variables the variables are: The strength of the acid. This will affect the amount of alkali needed to neutralise the acid, the stronger the acid the more alkali will be needed.
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Investigating the no. of moles of water of crystallization, in one mole of hydrated ethanedioic acid.
First you put 50 ml of distilled water into a beaker, and then you add the 1.5 g of acid, and dissolve it whilst stirring with a glass rod. When dissolved, you then put this solution into a conical flask, and make the solution up to 250 cm�, adding distilled water. When you have the 250 cm� of a solution, you put it into a volumetric flask, using a filter funnel. 3. Rinse a 25 cm� pipette with this solution, then pipette 25 cm� of the solution using pipette filler, into a conical flask.
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I predict that if the concentration is doubled the rate of reaction will double. This is because they are directly proportional to each other. Twice the concentration means twice the amount of Thiosulphate particles there are. So collisions happen twice as often which means all the Hydrochloric acid and Sodium Thiosulphate will react twice as fast. Sodium Thiosulphate + Hydrochloric acid � Sodium Chloride + Sulphur + Sulphur dioxide + Water Na2S2O3 (aq) + 2HCl (aq) � 2NaCl (aq) + S (s) + SO2 (g) + H2O (l) Ionic Equation: S2O3 (aq) + 2H (aq) � H2O (l) + S (s) + SO2 (g) Results Volume of Sodium Thiosulphate (cm�) Volume of Water (cm�)
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Use caution when dealing with chemicals. Hot boiling tubes and beakers can cause burns. Do not move around the lab during the experiment (stay at your work station) Scientific information on solubility The solubility of a solute in a solvent at a given temperature is the number of gram of that solute which can dissolve in 100g of solvent to produce a saturated solution at that temperature. In this experiment I will see how the solubility of potassium chlorate (KClO3) changes as the temperatures changes. Procedure I will explain my procedure in bullet points * Set up the Bunsen burner, tripod, gauze and the rest etc.
- Word count: 655
Acid-base indicators - explore some of the properties of selected acid-base indicators and measure the pH of some common solutions.
Methyl orange, phenolphthalein, universal indicator, litmus and bromothymol blue.) 2. Set up five test tubes in a rack, and then add about 2 ml of dilute hydrochloric acid (0.1 M) to each. To the first test tube add two drops of methyl orange and not any colour change. To the second tube add two drops of phenolphthalein and not the colour change. Continue for each indicator. Record your results in the table provided. 3. Repeat step 2using vinegar (which contains acetic acid), pure water (neutral), then 0.1 M sodium hydroxide (an alkali)
- Word count: 655
Halogenoalkanes react with an aqueous solution of hydroxide ions according to the equation: RX + OH- ? ROH + X- (X = Cl, Br or I) The following experiments examine the effect on the rate of hydrolysis when (a) the halogen is changed and (b) primary, secondary and tertiary halogenoalkanes and a halogenoarene are used. Ethanol is used as a common solvent for the halogenoalkane and for the silver nitrate solution. Water (from the silver nitrate solution) is used as hydrolysis agent in place of hydroxide ions, which tend to react too quickly for comparisons to be made.
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Result: Volume of NaOH used is recorded below: Trial (cm3) 1st time (cm3) Initial burette reading 3.55 18.4 Final burette reading 22.8 36 Titre 19.25 17.6 pH Chloroethanoic acid 3.0 Dichloroethanoic acid 2.2 Ethanoic acid 4.6 pH of chloroethanoic acid and dichloroethanoic acid is given by the teacher. Calculation: Ka = 1. It is reasonable to make the following assumptions: [HX] ??total acid concentration [X-] ??total salt concentration because CH3COOH is a weak acid which is only slightly ionized and thus contributed only a little bit to total salt concentration. Therefore [HX] tends to total acid concentration, and [X-] is mostly contributed by the salt resulting from neutralization.
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the solution would turn yellow, then a negative test with Tollen's Reagent, where no reaction would occur, showing that the compound cannot be oxidised. A carboxylic acid, propanoic acid, can be tested with sodium carbonate, a base, and carbon dioxide would be released, showing that the compound is an acid. This is a valid proof of a carboxylic acid in this group of compounds, as propanoic acid is the only acid. A primary alcohol, propan-1-ol, can be identified by first a negative test with 2,4-dinitrophenylhydrazine, showing it is not a carbonyl compound, then a positive test with acidified potassium dichromate, where the solution turns green.
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The effect of temperature on the rate of a reaction can be studied using the reaction between sodium thiosulphate solution and dilute hydrochloric acid.
Eventually, it is not possible to see a cross through the beaker.
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Oral contraceptives may increase the need for folic acid. Alcohol also can act as an enemy to folic acid absorption. Our bodies absorb the synthetic form of folic acid more easily than the natural form. A diet rich in folate is important, however the average American diet does not supply enough folic acid. For a list of foods rich in folate. Folic acid recommendation SBAA advises the 60 million women of childbearing age not to depend on food alone for folic acid.
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Anti-bumping granules were added to the pear shaped flask in order to prevent the sudden formation of large gas bubbles that lead to 'bumping' or large succussion. 3) A solution containing 5g sodium dichromate, (which is characteristically orange) in 5 cm3 of water and 4 cm3 ethanol was then prepared. The volume of water and ethanol were measured using a 10 cm3 measuring cylinder, whilst the sodium dichromate was weighed on a balance (which gives readings to 2 decimal places).
- Word count: 605
Preliminary experiment-For the preliminary experiment, my aims were; * To see how much Magnesium gives a reasonable time to react? * What concentration gives a reasonable time? * How do I change the concentration? * Can I repeat the experiment reliably? Test Tube Volume Water (cm ) Volume Acid (cm ) Reaction Time(s) 1 5 5 52.07 2 4 5 40.59 3 12 15 42.34 4 4 5 40.72 I chose to use 2cm piece of magnesium because it seems like a reasonable amount to use.
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Most people are familiar with pH as an indicator of how acid or alkaline a solution is. The pH scale ranges from 0 pH (very acidic) to 14 pH (highly alkaline).
Calibration is a process that allows the digital pH meter to acknowledge if any piece of testing equipment is performing to its up most of use and discharges any problems that it encounters. Like any laboratory instrument, pH meters need to be calibrated so that they provide accurate readings. A Digital pH meter uses an electrode to measure the pH of a solution. 1) Press the mode button to select pH. 2) Press the Set-up button twice, then press the 3)
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Measure the specific heat capacity of ball bearings and state what material the ball bearings are made of.
Apparatus 1. Ball bearings 2. Thermometer 3. Water 4. Beaker 5. Calorimeter 6. Bunsen burner 7. Platform balance 8. hot plate Procedure 1. Measure the temperature of the water using a laboratory thermometer at room temperature, and record the temperature. 2. Measure the mass of ball bearings and calorimeter and record. 3. Connect the balls using a string so as to make them move using the string so there will be no need in touching them. 4. Add water into the calorimeter at room temperature. 5. Add sufficient water into a beaker and place the ball bearings in it and then boil the water to 98�C.
- Word count: 713
Titration - The purpose of our experiment is to find the concentration of a sample of sulphuric acid accurately.
Stand and Clamp Conical flask Sulphuric (IV) Acid (n*50cm3 based on how many repeats are conducted) Prepared Sodium Carbonate Solution Methyl Orange Indicator (10cm3) Funnel Pipette Pipette filler White Tile Method Method for the production of Sodium Carbonate solution 1. Use the volumetric flask to get 250cm3 of distilled water 2. Place 2.65g of sodium carbonate in a petri dish (weighed on the electronic balance). 3. Pour the solid into a beaker. Wash the petri dish with some (perhaps 10cm3) of the 250cm3 distilled water so that all of the solid is used and place the washings in the beaker also.
- Word count: 675
There were 3 different types of water's we had to test for and they were - * Seawater - Na+, K+, Ca2+, Cl-, So42-, Co32- * Lake water - Ca2+, Cu-, Cl- * Bath water - Na+, Co32- Safety points. There were a few safety points that we had to be careful with so that the experiment would go right and that no one would get hurt. 1. Making sure that we wore goggles when doing the experiments. 2. Making sure that we don't get the chemicals onto us.
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In the Kolbe synthesis (also known as the Kolbe-Schmitt reaction) sodium phenoxide is heated with CO2 under pressure and the reaction mixture is subsequently acidified to yield salicylic acid. 2-hydroxybenzoic acid (salicylic acid) can be converted by straightforward reactions into two products, both of which find applications as medicines.
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Once the paste was formed more distilled water could be added so that the solution could be made. This was done to ensure that no lumps of sodium chloride formed. Distilled water was run over the weighing boat and allowed to flow into the beaker so that any sodium chloride which had not fallen out did so. The volumetric flask and the pipette were washed out with distilled water to ensure that there were no impurities. This solution was then poured into a volumetric flask. The beaker was washed out with more distilled water which was than added to the volumetric flask, this was to ensure that any solution that had been left behind was not lost.
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To investigate how different concentrations of acid affect the rate of a reaction with Magnesium ribbon and how long it takes for the magnesium to dissolve.
+ 2HCl (l) MgCl2 (aq) + H2 (g) Prediction: The higher the concentration of the Hydrochloric acid, the quicker it will take for the Magnesium ribbon to dissolve. To test my prediction is correct, I will use 4 different types of Hydrochloric acid concentrations, and these are 0.5M, 1.0M, 1.5M and 2.0M. I will also time how long it takes for the Magnesium ribbon to dissolve, for each of the concentrations. The quickest reaction will be with 2.0M and the slowest with 0.5M; this is because there are more acid particles reacting in the 2.0M.
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The temperature chosen is a compromise between these two factors. Ammonium nitrate is a hygroscopic white solid, which means that it will absorb moisture from the atmosphere. It is an oxidising agent that gives off nitrogen oxides, mainly nitrous oxide, when heated. It is normally made in the form of small white balls, about two millimetres in diameter. Fritz Haber invented the process used all over the world to make ammonia from nitrogen and hydrogen. He also devised gases for the World War effort on Germany's behalf, such as chlorine, phosgene and mustard gas.
- Word count: 516