Question

A 14.3 g sample of HF is dissolved into 250 mL of solution. The concentration of the solution is *

A. 2.86 M
B. 0.14 M
C. 7.1 M
D. 3.6 M

Answer 1

The concentration of the solution is 2.86 M

Step-by-step explanation:

Molarity is a unit of concentration based on the volume of a solution. It is defined as the number of moles of solute that are dissolved in a given volume. In other words, molarity is defined as the number of moles of solute per liter of solution.

The Molarity of a solution is determined by the following expression:

`Molarity (M)=(number of moles of solute)/(Volume)`

Molarity is expressed in units (
`(moles)/(liter)`).

In this case, you must then know the number of moles of HF, for which you must know the molar mass. Being:

• H: 1 g/mole
• F: 19 g/mole

the molar mass of HF is: HF= 1 g/mole + 19 g/mole= 20 g/mole

Then the following rule of three applies: if 20 g of HF are available in 1 mole, 14.3 g in how many moles will they be?

`moles=(14.3 g*1 mole)/(20 g)`

moles= 0.715

So:

• number of moles of solute: 0.715 moles
• Volume: 250 mL=0.250 L (being 1 L=1000 mL)

Replacing:

`Molarity=(0.715 moles)/(0.250 L)`

Solving:

Molarity= 2.86
`(moler)/(liter)`=2.86 M

The concentration of the solution is 2.86 M