Question G5 7th Edition

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Max Hayama 4K
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Joined: Fri Sep 28, 2018 12:16 am

Question G5 7th Edition

Postby Max Hayama 4K » Mon Oct 01, 2018 2:33 pm

A student prepared a solution of sodium carbonate by adding 2.111g of the solid to a 250.0mL volumetric flask and adding water to the mark. Some of this solution was transferred to a buret. What volume of solution should the student transfer into a flask to obtain (a) 2.15 mmol Na+ (b) 4.98 mmol CO3^-2 (c) 50.0mg Na2CO3

Having trouble understanding how to solve part A, especially since each formula unit has 2 sodiums. Can someone explain?

Brian Hom 2F
Posts: 60
Joined: Fri Sep 28, 2018 12:24 am

Re: Question G5 7th Edition

Postby Brian Hom 2F » Mon Oct 01, 2018 4:20 pm

So to solve part A, we want to find out what volume of solution is needed to have 2.15mmol Na+.

First we want to find out the concentration of Na+. 2.111g Na2CO3 divided by 105.99g Na2CO3 (molar mass). Then take that and multiply it by 2 since for every one Na2CO3 there are 2 Na+. Finally divide this answer by 0.2500L in order to find the concentration. You should get 0.1593M Na+.

Second we divide 2.15x10^-3 Na+ by the concentration we got (0.1593 M Na+) and get the answer 0.0135 L of solution.

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