Chemical quantities (AS)
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I have given the planning exercise for finding the solubility of calcium hydroxide by titrating it with HCl. Scale given for calcium hydroxide solution is 1.5g/1dm3. Now my question is how do you find the concentration of HCl for this titration?
I have tried to research this question on the site and I did see some relevant information but still my concept has not been clear. I would really appreciate if you explained how do you find the concentration when you have only the equation given.
110208
Corrie writes ....
First of all you need to work out the approximate concentration of the calcium hydroxide solution in mol dm-3, using the mass of 1.5 g/dm3 and the formula mass for calcium hydroxide. I presume you can do this?
Now let's assume, for the moment, that the calcium hydroxide and the HCl react in a 1:1 mole ratio in the titration. If the HCl used had a similar concentration, then the volumes of calcium hydroxide and HCl solution in the titration would also be in a 1:1 ratio. For example, if you titrated 25 cm3 calcium hydroxide solution, it should need 25 cm3 of HCl solution to neutralise it.
On the other hand, if we assume that HCl and calcium hydroxide react in a 2:1 mole ratio (you'll have to figure out or look up the balanced equation yourself to decide on the correct ratio), then 25 cm3 of calcium hydroxide solution would need 50 cm3 of HCl of the same concentration to neutralise it - a burette full!
In a titration one usually tries to pick a concentration for the known solution (HCl here) so that the titration value is of a similar volume to the volume of the unknown solution taken. Knowing the approximate calcium hydroxide concentration and the balanced equation, you should be able to select a value for the concentration of the HCl solution that willl give you titration values, based on the volume of calcium hydroxide taken, that are neither too small (a few cm3) or too big (more than a burette full).
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updated: 12 February 2008
