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?


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.

  • $\begingroup$ 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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