I wanna prepare 100mM cacl2 solution,help plz?

Question

I wanna prepare 100 ml Cacl2(100mM-mili Molar) solution ,how much Cacl2 should I weight and add too 100 ml water?how should I calculate?

Answer 1

First: Calculate the molar mass of CaCl2: 40.078+(35.453*2) = 110.984g

Second:You want a mM solution, so you must divide this mass by 1000 = 0.11098g

Third: This is the mass that should be diluted to 1000ml, but you want only 100ml, so you must divide again by 10 = 0.0111g.

Answer: dissolve 0.0111g CaCl2 in 100ml solution and you will have a mM solution.

Note: This is a very theoretical answer. It is very difficult to weigh out 11mg of any compound, and CaCl2 is even more difficult because it is very hygroscopic. In a practical laboratory you would prepare a stock solution with concentration of , as an example, 0.1M by diluting 11.1g of CaCL2 which you have weighed out rapidly and reasonably accurately. Then dilute to 1000 ml. Take 10ml of this solution and dilute again to 1000ml . This is a mM solution. But note that this is not a standard solution and you would have to standardise it by titrating against a standard AgNO3 solution to determine the exact concentration. It is really impractical to make an exact 100ml mM solution of CaCl2 directly