How many grams of na2s do we need to dissolve in 200ml of water to get a solution that is 0.2 m?

We know that the molarity of a solution is calculated by the following equation:



That being said we are given two of the 3 things that we need: Volume of water, as well as the molarity of the solution. Let's plug those in to the equation to find how many moles of  that we need:

=>

This means that we have 0.04 moles of .

In order to calculate the number of grams that we need for this solution, we must first calculate how many grams of are in 1 mole. We do this by taking the atomic masses of each element from the periodic table and adding them together.

Na = 22.99 g
S = 32.06 g

We have 2 Na's, and we have 1 S. So lets add them together:

2(22.99) + (32.06) = .

Since we need 0.04 moles of , we can multiply the molar weight of the molecule times the amount of moles needed to find the total grams that we need for the solution:



Now we know that in order to make a 0.2 M solution of , we must use 3.1216 grams.