How many grams of sodium bromide must be dissolved in 400.0 g of water to produce a 0.500 molar solution?

A20.0 g

B52.18

C2.00 g

D20.6 g

D. 20.6g

Explanation:

Molarity is defined as ratio between moles of solute (sodium bromide, NaBr) per liter of water.

As density of water is 1g/mL; volume of 400.0g of water is 400.0mL = 0.4000L.

That means 0.400L of 0.500M solution contains:

0.400L * (0.500mol / 1L) = 0.200moles of sodium bromide.

In mass (NaBr = 102.9g/mol):

0.200mol NaBr * (102.9g/mol) = 20.6g of NaBr

Right answer is:

D. 20.6g