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GCSE: Aqueous Chemistry

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The rates of aqueous reactions

  1. 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. 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. 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. 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.
  5. 5 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

  1. 1 The two most important equations to learn are:

    moles = mass / Mr and moles = volume x concentration
  2. 2 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. 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. 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. 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. 1 Anything that is dissolved in an aqueous solution will have the state symbols (aq). For Na+(aq)
  2. 2 If your reaction is dissolved in water, then water will have the state symbol (l), for “liquid”.
  3. 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. 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. 5 The most important equation reaction to remember is acid + base = salt + water. This crops up all of the time in exams!

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  1. To determine the concentration of a solution of ethandioic acid.

    Clean and rinse your graduated flask. Clean a burette and rinse with distilled water until the water drains cleanly from the inverted burette. 2. Fill the burette with the NaOH solution until the 'zero' mark with the aid of a funnel. Using a white tile placed behind the burette, at eye level, make sure the bottom of the meniscus touches the point zero. 3. Place the volumetric flask under the burette tap and fill the flask with 9-11 cm3 of NaOH solution.

    • Word count: 846
  2. An experiment to show the lowest concentration of copper (II) sulphate solution needed to bring about full denaturation of egg albumen.

    Another reason for the opaqueness is that the positive copper ions change the polarity of the albumen; this increases its insolubility and causes it to precipitate out of the solution. List of apparatus Colorimeter I have chosen this method of measuring the opaqueness of the egg albumen because it is a lot more accurate than eye and will give me figures that I can use in graphs, tables or charts. Distilled water this is use rather than tap water because it contains less impurities that could affect the experiment (e.g. copper ions from copper pipes.) results.

    • Word count: 617
  3. Finding out How Much Acid There Is in a Solution.

    Wash out the funnel with distilled water and place the water into the volumetric flask. Repeat this twice to ensure all powder is in the volumetric flask. Mix the sodium carbonate and water so that there is no trace of the powder. Add some distilled water and mix again. Repeat this until there is 250cm3 of the solution in the volumetric flask. Close the flask with the rubber bung, and turn it around to make sure all the powder has dissolved. Mix thoroughly. You now have a 0.5 moldm-3 solution on sodium carbonate. 3. Clamp the burette to the lab stand, and clamp the lab stand to the table using the g clamp.

    • Word count: 847
  4. Acid Base Theories: Svante Arrhenius.

    and his defence a third class (c*m laude approbatur - approved with praise). Essentially, he got a grade of D for the dissertation and a C for his defence. He could not obtain a job within his native Sweden, but he did get a travel grant and worked outside the country for several years. He did return in 1891, but even in 1895, his elevation to Professor of Physics was bitterly opposed as was his overdue election to the Swedish Academy of Sciences in 1901.

    • Word count: 704
  5. Problems with old age.

    One of the most dangerous aspects of life in this Day in age is fire. Many people know that the danger in fire is the smoke and I think if can be detected before it gets really bad it can be attended to with ease. I know that there are smoke alarms on the market but I don't have one at home so I thought I would make one instead of having to buy an expensive one.

    • Word count: 434
  6. Does caffeine affect heart rate?

    Method * Cut sections from a single beetroot. Cut eight, 1cm length slices from these sections. * Place the slices in a beaker of distilled water. Leave overnight to wash away excess dye. * Next day, place eight labelled boiling tubes each containing 5cm3 distilled water into a water baths at 0, 10,20,30,40,50,60 and 70 degrees. Leave for 5 minutes until the water reaches the required temperature. Place one of the beetroot sections into each of the boiling tubes. Leave for 30 minutes in the water baths.

    • Word count: 912
  7. Who's cheating on the vinegar?

    It is a weak acid with a pH of 3. Alkalis have a pH of 8 or above. We will be using Sodium hydroxide which is a strong alkali of 14. An indicator is something which is one colour in an acid and another in an alkali. This means you use it to show what pH value a soultion is. Common indicators are, litmus and methyl orange but we will be using Phenolphthaleins. This is colourless in an acid but it goes bright pink in an alkali. This means that the solution will turn pink when it turns from an acid to an alkali.

    • Word count: 710
  8. To find the accurate concentration of Sulphuric (VI) Acid that has a concentration between 0.05 and 0.15 mol dm.

    This is done by using the mass of 1 mole (calculated in step 1) and multiplying it by 0.1. I am finding the concentration of 0.1 as the concentration of the Sulphuric Acid is thought to be between 0.05 and 0.15 mol dm� and 0.1 is an average of these two concentrations. 3. The mass that was calculated in step 2 would make up the mass if the solution was 1000cm�, but its not as I am using 250cm� as this the total volume of the Volumetric flask I am given. So to change this so that it will be the mass of 250cm� divide the calculation in step 2 by four.

    • Word count: 627
  9. Bacterial Leaching.

    The bacteria convert sulphide minerals into a solution containing Cu2+, Fe2+, Fe3+, and SO42- ions in an aqueous solution. The impermeable base layer means that it is easy to drain off the solution containing the copper ions. The solution then flows to an open pond where the Fe2+ ions are oxidised into Fe3+ ions by the thiobacillus ferro-oxidants. This recharges the leaching solution, which can then be pumped back to the top of the pile and reused. The copper ions are extracted from the leaching solution by a process called 'ligand exchange solvent extraction.'

    • Word count: 791
  10. Investigating an equation .

    , this will keep the depth of the solution the same each time so that the optical properties of the liquid to not change . Using a burette to make up the desired concentration of sodium thiosulphate diluting with distilled water if required , pipette 50 cm into a conical flask . Pipette 20 cm of HCl into a test tube , pour the contents of the test tube into the conical flask . When the last of the HCl enters the flask I will start a stop watch , recording the amount of time it

    • Word count: 561
  11. Acid rain - With this experiment we want to show how gases that are dissolved in water will turn the water into an acid.

    Then we placed a match in a clean beaker and lighted it. We covered the beaker with a lid. When the match had burned out we added bromothymol blue solution from the test tube to the beaker. Afterwards we shook the beaker to make sure it mixed. In the cupboard we heated a spatula of lead nitrate in a test tube. We observed how the lead nitrate decomposed to lead(II)oxide, PbO, and nitrogen dioxide, NO2. When heavy fumes of nitrogen dioxide occurred we immediately poured them into a clean beaker. Again we added bromothymol blue solution from the test tube to the beaker and shook it vigorously.

    • Word count: 559
  12. To determine the percentage of hydrochloric acid in a sample of diluted concrete cleaner.

    Discussion Questions: 1) The manufacturer states there is 33% w/v HCl in the concrete cleaner. This is equivalent to 330g of HCl per 1L of solution. Therefore stoichiometry can be used to determine the expected molarity of the acid. 2) The mass of concrete cleaner is the mass of the volumetric flask with the sample in it subtracted from the weight of the clean dry volumetric flask.

    • Word count: 567
  13. To find if changing the concentration of an acid will increase or decrease the rate of the reaction when marble is dissolved in hydrochloric acid.

    I will use Marble chips all of which will be weighed for 3g for each different concentration. The amount of acid concentration I have decided on is 50cm3 I will firstly select the first concentration of acid, which will be the lowest concentration solution, which is 40cm3 acid and 10cm3 water and measure that out. Place the marble chips in the flask and then as quickly as possible place the acid concentration into the flask and apply the stopper, which is connected to the tube.

    • Word count: 878
  14. In a neutralisation reaction between an acid and an alkali, water is formed. Experiment to prove this.

    In the experiment I am going to use Sodium Hydroxide and Hydrochloric Acid. Therefore my formula is: NaCl(aq) + HCl(aq) = NaCl(aq) + H2O(l) There must be equal amounts of hydrogen ions (from the hydrochloric acid) and hydroxide ions (from the sodium hydroxide) for the solution to be neutral. Prediction: After some preliminary tests, I believe that as the concentration of alkali increases the amount of acid needed to neutralise it will increase. This is because there are less hydroxide ions in 25cm of sodium hydroxide then there is hydrogen ions in 25cm of hydrochloric acid.

    • Word count: 480
  15. Chemical reactions of the elements - Reaction of titanium with air.

    + 2H2O(g) TiO2(s) + 2H2(g) Reaction of titanium with the halogens Titanium does react with the halogens upon warming to form titanium(IV) halides. The reaction with fluorine requires heating to 200�C. So, titanium reacts with fluorine, F2, chlorine, Cl2, bromine, I2, and iodine, I2, to form respectively titanium(IV) bromide, TiF, titanium(IV) chloride, TiCl, titanium(IV) bromide, TiBr, and titanium(IV) iodide, TiI. Ti(s) + 2F2(g) TiF4(s) [white] Ti(s) + 2Cl2(g) TiCl4(l) [colourless] Ti(s) + 2Br2(g) TiBr4(s) [orange] Ti(s)

    • Word count: 535
  16. This is an experiment to determine relative rates of hydrolysis of the halogenoalkanes.

    Aim The task is to design an experiment that would be suitable for investigating whether the electonegativity of the halogen or the bond polarity and strength affects the rate of hydrolysis. Therefore, which halogenoalkane reacts faster? Equipment * 6 test tubes * Rubber bands * Teat Pipettes * Beaker * Thermometer * Measuring cylinder * Stop clock * 1 - Chlorobutane * 1 - Bromobutane * 1 - Iodobutane * Ethanol * Silver nitrate solution The rate of reaction can be followed by carrying it out in the presence of silver ions.

    • Word count: 835
  17. The Relative Formula Mass of an Unknown Acid.

    Add 3-4 drops of phenol red indicator to the sodium hydroxide solution. (The indicator changes from pink in alkaline solution, to yellow in acid solution. The endpoint is reached when the solution first changes colour to orange.) 4. Run the acid solution from the burette into the flask, with continuous swirling, until the solution just loses the pink colour and goes orange. This first result may be used as a trial run because you will probably overshoot the endpoint on the first attempt. Record the final burette reading. 5. Refill the burette with the acid solution, again to 0cm3.

    • Word count: 769
  18. The dehydration of Cyclohexanol to form Cyclohexene.

    Because of this all products collected in the vented receiver below 340K were discarded. In order that water was not present inside the vented receiver or any other component of the apparatus before the experiment began, all components were cleaned with acitone. Once the experiment had been set up the mixture was heated with a Bunsen burner to a temperature of around 363K where it was kept in order to increase the speed at which the Cyclohexene was collected in the vented receiver.

    • Word count: 817
  19. The Percentage Purity of an Unknown Acid.

    Titration no. 1 2 3 4 5 Initial reading 0.00cm3 0.05cm3 22.30cm3 1.05cm3 0.00cm3 Final reading 23.15cm3 22.25cm3 44.60cm3 23.55cm3 22.30cm3 Titre value 23.15cm3 22.20cm3 22.30cm3 22.50cm3 22.30cm3 Analysis To calculate the mean titre value I simply added the last four values together (2-5) and divided by four. I decided to exclude the first value as this wasn't concurrent with the others and was most likely only a trial run (to get a rough estimate to work towards). The rest were all within quite a small range and so using this first value could lead to inaccuracies in calculations carrying on through the investigation from the very start.

    • Word count: 895
  20. Determination of the relative atomic mass of lithium

    Ar = 0.10 / 0.016 = 6.383 (3dp) Calculations - method 2 LiOH + HCl LiCl + H2O 1 mole 1 mole 0.10 34.96 / 1000 = 0.003496 moles = 0.0035 (2sf) moles in 25cm�of LiOH 0.003496 x 4 = 0.013984 moles = 0.014 (2sf) moles in 100cm� of LiOH Ar = 0.10 / 0.013984 =7.15 (2dp) Evaluation Overall both of the procedures for finding the relative atomic mass of lithium were relatively successful although none of them were 100% accurate: * The biggest percentage error was in the weighing of the lithium because the scale only weighs to 2 decimal places therefore the mass could have been as much as 0.10g plus or minus 0.005g which gives a 5 percent error margin.

    • Word count: 607
  21. Titration Theory - Titration is a laboratory technique by which we can use to determine the concentration of an unknown solution using a standard concentration of another solution that chemically reacts with the unknown.

    We also pre-measure the volume of the unknown. We then titrate with the standard from a burette into the container with the measured unknown and the chemical indicator until the indicator either turns colour or a precipitate indicates that the end point or the equivalence point has been reached. Having the initial and final readings of the titrant burette gives us the volume of the titrant used.

    • Word count: 598
  22. An investigation into how the concentration of a substance effects the reaction time

    But if more units of water are exchanged for units of the solution the reaction will slow down. The more water that the solution contains the longer the reaction will take due to the particles are more spread out and will take longer to collide. After comparing my ideas with the results I have seen on the Internet I can safely say that my prediction is correct. Apparatus Conical Flask Hydrochloric acid Picture of a black X Stop Clock 3 Measuring Cylinders Water Beaker Goggles Sodium Thiosulphate Diagram Sodium Thiosulphate Hydrochloric acid X (underneath the Conical Flask)

    • Word count: 718
  23. Determination of the relative atomic mass of Lithium using Titration.

    Collect the gas evolved. Record the final volume. KEEP THE SOLUTION IN THE CONICAL FLASK FOR METHOD 2 Diagram for method 1 Result table START (water in measuring cylinder) cm3 FINISH (water after gas was produced) cm3 DIFFERENCE (Gas was collected) cm3 36 176 176-36 = 140 Calculation Assuming that I mole of gas occupies 24 000cm3 at room temperature and pressure 2Li(s) + 2H20(l) 2LiOH(aq) + H2(g) (2 moles) (1 mole) (44.8dm-3) (24 000) 2Li : H2 Therefore the ratio is 2 : 1 1. No. Of moles of hydrogen = 140/24 000 = 0.0058 moles 2. No.

    • Word count: 834
  24. Acid Rain Analysis

    By 70ml it had dropped by 3.2ml. From 80ml-100ml it began to fall at a steady rate again. Processed Evidence: Using the line of best fit on the graph, I can conclude that at 45ml oxygen volume would be about 7.3ml, and at 75ml the oxygen volume would be 2.3ml. This further backs my theory that the rate of oxygen fell at a steady pace between 10ml and 40ml, but drastically dropped between 50ml and 70ml. Conclusion: From the graph I have come to the conclusion that the acid concentration did affect the rate of oxygen produced.

    • Word count: 646
  25. The determination of the Ar of Lithium.

    Mass = Ar Number of moles 0.10g = 6.452 0.0155 Titration LiOH(aq) + HCl(aq) ? LiCl(aq) +H2O(l) In the Titration there were 0.0139 moles of HCL (Hydrochloric Acid). Concentration x Litres = Number of moles 0.1 x 0.139 = 0.0139 moles There were 0.0139 moles of LiOH (Lithium Hydroxide). Concentration x Litres = Number of moles 0.1 x 0.139 = 0.0139 moles In 100cm3 of the solution from method 1 there were 0.139 moles of LiOH (Lithium Hydroxide)

    • Word count: 534

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