Dilution Problem G5 from tetxbook

[alexandralopez 3F]

Hi guys! I'm reviewing the dilution problems from the textbook to prep for the midterm and I'm stumped on what to do for G5:

A student prepared a solution of sodium carbonate by adding 2.111 g of the 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) 2.15mmolNa+; (b) 4.98mmolCO32−; (c) 50.0mg Na2CO3?

I'm currently working on part a and so far I've found the molarity of Na2CO3, which was 0.07967 and the molarity of NA+ by multiplying 0.07967 by 2 but I'm not sure what do after this. Can anyone help?

[Crystal Yu 1D]

The basic way to solve these problems is using the given value in part a and conversion factors and ratios to find out how many ml of the solution is needed to obtain the wanted amount.

Based on what you have so far though, you can use the dilution formula M1V1 = M2V2, where M is the molarity and V is the volume.

I have attached my work for this problem below if it helps!

[Wasila Sun 2I]

For part c, I would begin by changing the mg of Na2CO3 into moles of Na2CO3. This can be done by changing mg into grams by dividing by 1000 and then changing grams to moles by dividing grams by the molar mass of Na2CO3 which is 105.99 g/mol. The resulting asnwer should be around 0.000472 mol Na2CO3. Then to find the volume of the solution we need, we use the v=n/c equation to divide number of moles we found by the molarity.