Dilution Question

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Elle_Mendelson_2K
Posts: 72
Joined: Fri Sep 28, 2018 12:28 am

Dilution Question

Postby Elle_Mendelson_2K » Wed Oct 10, 2018 4:43 pm

Hello! Will someone explain G5, from the 7th edition textbook?
I understand how to find the Molarity of the compound in the solution, I just don't understand why when finding how much volume of the solution to obtain 2.15 nmol of Na+ you multiply the 2.15X 10^3 mol of Na / 0.0796 by 1mol of Na2CO3/ 2 mol of Na +. Shouldn't you multiply it by 2 mol of Na +/ 1mol of Na2CO3?
Thank you!

Diane Kang 2F
Posts: 33
Joined: Fri Sep 28, 2018 12:18 am

Re: Dilution Question

Postby Diane Kang 2F » Wed Oct 10, 2018 5:24 pm

You multiply (1 mol Na2CO3) / (2 mol Na+) instead of (2 mol Na+) / (1 mol Na2CO3) because the Na+ and Na2CO3 do not cancel out if you multiply (2.15 * 10^3 mol Na+) / (0.076 mol Na2CO3 / L).

[(2.15 * 10^3 mol Na+) / (0.076 mol Na2CO3 / L)] * [(1 mol Na2CO3) / (2 mol Na+)] simplifies to
[(2.15 * 10^3 mol Na+) * L] / 0.076 mol Na2CO3 * ((1 mol Na2CO3) / (2 mol Na+)).

Using dimensional analysis, you can find the volume of solution needed.


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