Q. G5

[Moris 1H]

Could someone help me with this question? It's about molarity and dilutions. I understand how to find the molarity of the solution but how do you find specific volumes to obtain specific moles? I don't really understand the concept behind it either.

Question:
A student prepared a solution of sodium carbonate (Na₂CO₃) by adding 2.111g 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) 2.15 mmol Na⁺; (b) 4.98 mmol CO₃^2-; (c) 50.0 mg Na₂CO₃?

[hannahtweedy]

a) First, you convert the mmol to mol - keeping in mind since there's 2 Na in Na2CO3 the molarity will be doubled. Then you can divide the values in the formula: 0.002015/0.16 --> 0.013 L