Fundamentals G.5 (part a)

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Fundamentals G.5 (part a)

Postby kellyz_1C » Tue Apr 10, 2018 8:19 pm

The question is this:

A student prepared a solution of sodium carbonate by adding 2.111 g of solid to a 250.0-mL 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 mm Na+; (b) 4.98 mmol (CO3)^2- ; (c) 50.0 mg Na2CO3?

The solutions manual calculated part a without including the final volume; I'm not quite sure what they did. They also divided by 2 mol of Na+, but I'm not sure why that's necessary. I tried solving this question just by using MiVi = MfVf but got a different answer.

Can anyone explain?

Posts: 31
Joined: Fri Apr 06, 2018 11:05 am

Re: Fundamentals G.5 (part a)

Postby princessturner1G » Tue Apr 10, 2018 10:54 pm

Remember that M= mol/liters or Liters= mol/M so to calculate the volume we would have to find M first.
You can find this by 2.111g/(105.99gmol^-1)(.2500L) = 0.07967 M
Now that you have M you can solve for volume by plugging into in V= mol/M
V= (2.15*10^-3 mol Na+)/ (0.07967 molL^-1 Na2CO3)(2mol Na+)
You then get 1.35*10^-2 L.

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