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I have a chemical formula with $27\%$ $\ce{CaCl2.6H2O}$ and $43\%$ water with the balance of $30\%$ being other chemicals.

I want to convert the $\ce{CaCl2.6H2O}$ and water percentage to $\ce{CaCl2.2H2O}$. I understand molecular weight percentage of $\ce{CaCl2}$ is higher in $\ce{CaCl2.2H2O}$ so I expect the percentage of calcium chloride will increase but I'm unable to calculate by how much.

Can you please show me how to calculate?

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Do you understand that you're trying to do $\ce{CaCl2.6H2O -> CaCl2.2H2O + 4H2O}$? Just assume that in the beginning you had $\pu{100 gm}$ of the total mixture. So that makes the weight of $\ce{CaCl2.6H2O}$ present in the intial mixture to be:

$27\%$ of $\pu{100 gm = 27gm}$.

Next, calculate the number of moles of $\ce{CaCl2.6H2O}$ you had in the beginning by:

dividing the mass you've just obtained by the molecular mass of this compound.

Now according to the stoichiometry of the reaction I've given you, when $1$ mole of $\ce{CaCl2.6H2O}$ converts, you get $1$ mole of $\ce{CaCl2.2H2O}$. Can you calculate the mass of $\ce{CaCl2.2H2O}$ thus obtained? So now you've the mass of $\ce{CaCl2.6H2O}$ and $\ce{CaCl2.2H2O}$.

To calculate the percentage of $\ce{CaCl2}$ in $\ce{CaCl2.2H2O}$ all you've got to do is:

$\displaystyle \frac{\text{Mass of } \ce{CaCl2}}{\text{Mass of } \ce{CaCl2.2H2O}} \times 100\%$

You can carry out this step for $\ce{CaCl2.6H2O}$ on your own and then finally calculate the percentage change.

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  • $\begingroup$ Hi Berry,Thank you so much for your really well laid out answer. $\endgroup$ – jane May 27 '17 at 2:32
  • $\begingroup$ Hi @Berry Holmes,Thank you so much for your really well laid out answer. OK bear with me as i'm new at this. Is the number of moles of Cacl2.6H20 27/219 =0.123 ? To calculate mass of CaCl2.2H20 147 g .? therefore is the % of cacl2 in cacl2.2h20 111/147? = 75% ? And so is the % of cacl2 in cacl2.6h20 108/219 = 49.3%. So therefore75%/49.3% = 1.52. Does this mean Berry to convert 27% ofCacl2.6H20 to a % of Cacl2.2H20 = 27% * 1.52 = 41.07 % Cacl2.2h20 = 27% Cacl2.6H20 ?????. Thanks for your efforts Berry I really appreciate it :) $\endgroup$ – jane May 27 '17 at 2:43
  • $\begingroup$ @jane If your calculations are correct I see no flaw in your reasoning, and that's a good method; I hope you're getting a correct answer! Also, I'm pretty sure you're running low on time, but the next time you ask a question here please add whatever you've done (that's called showing your effort) and we'll all be glad to help you! $\endgroup$ – Berry Holmes May 27 '17 at 14:40
  • $\begingroup$ thank you for your reply and feedback. I still feel like I am fumbling my way through. Was my calculation figure above of 75/49,3 = 1.52 the correct figure to convert CaCl2. 6H20 to CaCl2.2H20 ? $\endgroup$ – jane May 29 '17 at 11:59
  • $\begingroup$ Thank you so much. You see even if my reasoning and hopefully calculations are correct i dont know if they are actually correct. Hope to hear from you and sorry to waste your time Berry $\endgroup$ – jane May 29 '17 at 12:02

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