Question

We take 100 cc of a solution with a pipette from a bottle of hydrochloric acid with 30% of mass and density 1,15 g/cc. How many moles of hydrochloric acid are there in this volumen of hydrochloric acid?

Answer 1

0.945 moles of hydrochloric acid are there in this volume of hydrochloric acid.

Step-by-step Explanation:

Given:

• Volume taken = 100 cc
• Mass % of Hydrochloric acid in bottle = 30 %
• Density of the Hydrochloric acid solution = 1.15 g/cc

To be Found:

Number of moles in that volume of acid

Concepts used:

• Mass % is a way of representing the quantity of various components in a mixture.
• If we have a mixture of A and B, and we say that A has mass % to be 20%, we mean that for 100 g of the mixture, it contains 20 g of A substance.
• 1 mole of any compound has a mass equal to its Molecular mass
• The Molecular mass of $HCl =$ atomic mass of $H$ + atomic mass of $Cl$ = $1+35.5=36.5 \hspace{1 mm}g$

We can see in the question that we took 100 cc of the acid mixture. Since, the density is given and we know the volume, we can find out the mass of 100 cc of the solution.

$density= mass / volume\\or, mass = volume * density$

So, $mass= 100 * 1.15 = 115 \hspace{1 mm} g$

Now we know that the solution contains 30 % of $HCl$ by mass.

So, mass of $HCl$ = $30\% * 115\hspace{1 mm} g= 0.3 * 115\hspace{1 mm} g= 34.5 \hspace{1 mm} g$

Now let us apply unitary method to find the number of moles in this mass of acid.

36.5 g of $HCl$ occupies = 1 mole

⇒ 1 g of $HCl$ occupies = $1/36.5$ mole

⇒ 34.5 of $HCl$ occupies= $34.5/36.5 = 0.945$ moles

So, 0.945 moles of hydrochloric acid are there in this volume of hydrochloric acid.