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Determine the concentration of a limewater solution.

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Introduction

Name: Aisha Trew Candidate Number: 6535 Centre Name: Bullers Wood school Centre Number: 14217 To determine the concentration of a limewater solution Aim: To do an acid based titration to find out the concentration of limewater Introduction In this experiment, an acid-alkali titration will be done between calcium hydroxide and hydrochloric acid to find out the exact concentration of calcium hydroxide. Acid + alkali � salt + water Hydrochloric acid + calcium hydroxide � calcium chloride + water Symbol equation 2HCl(aq) + Ca(OH)2(aq)� CaCl2(aq) + 2H2O(l) I'll be using phenolphthalein indicator because it is good with strong acid and alkalis, it will be added to the hydrochloric acid which will turn the solution pink/red, when the solution is neutralise, therefore the end of the titration the solution will then turn clear. The concentration of the hydrochloric acid given is 2.00 mol dm-3 which is too concentrated to titrate the calcium hydroxide. To find the concentration needed to neutralise the calcium hydroxide which concentration is approximately 1 g dm-3. ...read more.

Middle

* Fill the concentrated hydrochloric acid in the graduated syringe up to 2.5 cm3. * Put the hydrochloric acid from the graduated syringe into a 250cm3 beaker, and add diluted water until the 250cm3 mark and stir with a glass rod. * Then pour into a 250cm3 volumetric flask and fill until 250cm3 mask accurately, this is done by filling up until the bottom of the meniscus measures from the eye level. * Get the 250cm3 of calcium hydroxide from a beaker use a 25cm3 pipette and put it into a conical flask * Place the conical flask on top of a tile * Set up the clamp and stand to hold a burette * Fill the burette with the diluted hydrochloric acid making sure the bottom of the burette is filled with hydrochloric acid. * Put the burette on the clamp, and record the starting point of the acid * Add a few drops of phenolphthalein indicator into the calcium hydroxide and it will turn the solution pink/red * Put the conical flask underneath ...read more.

Conclusion

The moles used per titration = volume x concentration = 0.02 x (31.8/1000) = 0.000636 mol As the chemical equation is: [2HCl(aq) + Ca(OH)2(aq) � CaCl2(aq) + 2H2O(l)] Ratio of HCl and Ca(OH)2 is 2:1 Therefore moles of calcium hydroxide: 0.000636 /2 = 0.000318 Concentration of Ca(OH)2 = moles/volume = 0.00318/(25/1000) = 0.01272 mol dm-3 Concentration of Ca(OH)2 in g dm-3 = concentration x mr = 0.01272 x (40.1+(16 x 2) +2) =0.01272 x 74.1 = 0.94 g dm-3 (2.d.p) Evaluation At the beginning of the experiment, you were told that the limewater given to you was just approximately 1 g dm-3. The answer calculated is 0.94 g dm-3, which is only 0.06 away from the approximated amount. The average concentration found of the limewater solution is 0.76 g dm-3. My results were 0.18 g dm-3 more concentrated than the average. This could be because the titration method as it is difficult to get the exact volume of hydrochloric acid needed to neutralise the calcium hydroxide solution that is why everyone final concentration for calcium hydroxide was slightly different. ...read more.

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