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concetration of limestone

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AS Chemistry Coursework - To Determine the Concentration of a Limewater Solution Aim To determine the concentration of a limewater solution using hydrochloric acid with a known concentration of 2.00 moldm-3. Introduction The initial idea of how to carry out this task is with a titration, however before this can be achieved other tasks have to be carried out. We know the limewater has a concentration of approx 1g dm-3 and the HCl has a concentration of 2.00 moldm-3 so the concentration of HCl has to be reduced. The second issue with the titration is which indicator to use. The indicator will be used to show the point where the solution becomes neutral when all of the base has been reacted. From Understanding Chemistry, for the indicator it is important that: * The indicators colour change is sharp so one drop of acid will cause the colour to change instantly rather than it changing gradually as more acid is added. * The colour change happens at the equivalence point which is the point where the amount of hydroxide ions equals the amount of hydrogen ions. * The colour change is distinct which would make it easier to see when the solution has been neutralised; a good example of this is phenolphthalein. ...read more.


& Pipette pump * Standard Flask (500cm3 capacity) * Beaker (500cm3 capacity) * 50cm3 of HCl solution of concentration 2.00mol dm-3 * 900cm3 of de-ionised water 1. Use the pipette and pipette pump to transfer 50cm3 of HCl solution into the standard flask. Fill the pipette to the fill line indicated; the bottom of the meniscus is the level of the solution. If the capacity of the pipette is only 25cm3 then this must be done twice to transfer the full 50cm3. 2. Fill the standard flask with 450cm3 of the de-ionised water, the fill line is also indicated, this must be exact, if the level goes over this line, the preparation of the HCl must be started over. Shake the flask with the lid on to ensure the solution is mixed. 3. Empty out the flask into the beaker then wash out the flask. 4. Move 50cm3 of the new HCl solution from the beaker into the flask using the same method as in Step 1. 5. Repeat step 2. 6. Empty out the beaker and wash out and then transfer then solution from the flask to the beaker. ...read more.


To convert from cm3 to dm3, divide by 1000. For the calculations V will be used to represent this volume in dm3. Known information: HCl Ca(OH)2 Moles / moles ? ? Volume / dm3 V 0.025 Conc. moldm-3 0.02 ? Moles can be worked out using the equation Concentration = Moles / Volume Moles = Concentration x Volume = 0.02 x V The reaction shows that two moles of HCl react with one mole of Ca(OH)2 so in the neutralisation there must have been twice as many moles of HCl than Ca(OH)2 . Therefore moles of Ca(OH)2 must be (0.02 x V) / 2 = 0.01 x V Again using Concentration = Moles / Volume : Conc. of Ca(OH)2 = (0.01 x V) / 0.025 = 0.4 x V The number of moles in dm3 will be concentration x1 which is 0.4 x V x 1 = 0.4 x V. The mass of the Calcium Hydroxide in the solution can now be worked out using Moles = Mass / Mr --> Mass = Moles x Mr Mr(Ca(OH)2) = 40 + 2(16 + 1) = 74 Mass of Calcium Hydroxide in dm3 = 0.4 x V x 74 Therefore the concentration of the Limewater in gdm-3 will be: 0. ...read more.

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