Question

A solution is prepared by dissolving 15.0 g of NH3 in 250.0 g of water. The density of the resulting solution is 0.974 g/mL. The molarity of NH3 in the solution is ______. A) 60.0 B) 3.24 C) 0.882 D) 0.00353 E) 3.53

Answer 1

Step-by-step explanation:

Answer: B

First we need a plan to solve this problem. Ultimately we want to get to our equation of molarity= moles of solute ÷ volume of solution (L). In order to get the volume of solution, we can use: Density = mass ÷ volume. So, 0.974g/mL=
`(265.0g)/(Volume (mL))` . Then we can solve for volume and get 272mL of solution. We then need to convert mL to L in order to use this in our molarity equation so 272mL(
`(1L)/(1000mL)`) = 0.272L of solution.

Now we need to find moles of NH3 by converting grams to moles using molar mass. The molar mass of NH3 is 17.031g/mol and we have 15.0 grams. Therefore 15.0g(
`(1 mol)/(17.031g)`) = 0.881mols of NH3.

Finally we can plug this into our molarity equation: Molarity =
`(0.881mols)/(0.272L)`= 3.14mols/L of NH3.