How many ml of concentrated HCL (36% HCL by mass, density= 1.18 g/my) are required to produce 10L of a solution that has a pH of 2.05?

Answer 1

To solve this, we will work backwards.

Step 1: find the molarity of the desired solution. The concentration of H+ in the solution is equivalent to the molarity of the solution.

[H+] = 10^(-pH)

[H+] = 10^(-2.05) = 0.0089125 M HCl desired

Step 2:

Now we can use the 10L volume to find out the moles of HCl in the solution

Molarity = moles/Volume

0.0089125 = moles /10

moles = 0.089125 mol HCl

Step 3: Let’s figure out how many grams this is by multiplying by the molar mass of HCl

H: 1.008 g/mol

Cl: 35.45 g/mol

Molar mass HCl = 36.458 g/mol

0.089125 mol * 36.458 g/mol = 3.249 grams HCl

Step 4: Find the mass of the concentrated solution. We know the solution is 36% HCl by mass, and we know that the mass of HCl we need is 3.249 grams. Let’s set up an equation to find the total mass. (remember we have to use a % as a decimal when putting it into an equation -> it will be 0.36)

Mass * 0.36 = 3.249 divide by 0.36 on both sides

Mass solution = 9.026 grams

Step 5: Convert grams to mL using the given density.

The density of the solution is 1.18 grams/mL and in general,

Density = mass/volume

We know how many grams of solution we have, so we will be solving for the mL.

1.18 = 9.026/volume multiply both sides by volume

1.18* volume = 9.026 divide by 1.18 both sides

Volume = 7.65 mL of concentrated solution. ANSWER

You will measure 7.65 mL of concentrated solution, then pour enough water in so that your final solution is 10L in volume. This solution will have a pH of 2.05. :)