Question

What is the molarity when 40 grams of HF is added to water to make a 500 ml solution?

Answer 1

Answer:

molarity is 4M

Explanation:

Given

mass(m) = 40g

Volume (V) = 500mL = 0.5 L

Molar mass of HF = 1 + 19 g/mol

= 20 g/mol

No. of mole = mass/molar mass

= 40/20 mol

= 2mol

Molarity(M) = no. of mole/volume of solution(L)

= 2/0.5 mol/L

= 4 mol/L

Answer 2

Given,

A solution contains 40 grams of HF added to water.

Amount of the solution = 500 mL

To find,

The molarity of the solution.

Solution,

We can simply solve this numerical problem by using the following process:

As per the principles of chemistry;

Molarity of a solution

= (moles of solute)/(volume of the solution)

The molar mass of HF

= atomic mass of H + atomic mass of F

= 1 gram + 19 grams

= 20 grams

Now, as per stoichiometry;

20 grams of HF is equivalent to 1 mole of HF

(As 1 mole of any compound weighs equal to its molar mass)

=> 1 gram of HF is equivalent to 1/20 moles of HF

=> 40 grams of HF is equivalent to 2 moles of HF

And, the solution in the question has HF as the solute and water as the solvent.

Now, according to the question;

The molarity of the solution

= (moles of solute)/(volume of the solution)

= (moles of HF)/(volume of the solution)

= 2 moles/500 mL

= 2 moles/0.5 L

= 4 mol/L = 4 M

Hence, the molarity of the solution is equal to 4 mol/L, that's is equal to 4M.