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Question

An aqueous solution of hydrobromic acid is standardized by titration with a 0.119 M solution of barium hydroxide. If 24.1 mL of base are required to neutralize 26.8 mL of the acid, what is the molarity of the hydrobromic acid solution?

Answer 1

Hi Alexandria,

Neutralization in Chemistry means that there is no excess of H⁺ or OH^- ions present in solution, as the chemical reaction between an acid (HBr) and a base (Ba(OH)₂) yields a salt and water. In this case a base of known molarity was used to standardize an acid of unknown molarity, meaning the base was used to determine the molarity of that acid.

The problem states that 24.1 mL of Ba(OH)₂ was used to neutralize 26.8 mL of HBr. This means that 24.1mL of Ba(OH)₂ solution provided enough OH^- ions to react with the H⁺ ions provided by the acid to form water, HOH (H₂O). Here is how we determine the molarity of the acid from the information provided about the base.

1. Convert the volume of the base from units of mL to L by dividing by 1000, as follows: 24.1 mL of Ba(OH)₂ ---> 0.0241 L of Ba(OH)₂. We do this because the rest of the solution uses units of molarity, which is moles/L.
2. Use the given molarity and volume of Ba(OH)₂ to determine the number of moles of Ba(OH)₂: 0.0241 L Ba(OH)₂*(0.119 mol/L of Ba(OH)₂) --> 0.002868 mole Ba(OH)₂ . Once you multiply the molarity (mol/L) by the volume (L) of Ba(OH)₂, you end up with units of moles of Ba(OH)₂.
3. For every Ba(OH)₂ molecule, there are 2 OH^- ions, as you can see by the chemical formula of Ba(OH)₂. So, to find the total moles of OH^-, we multiply the number of moles of Ba(OH)₂ by 2, as follows: 0.002868 mole Ba(OH)₂* 2 --> 0.005736 mole OH^-
4. In this step, we use the moles of OH^- ions to determine the moles of the H⁺ ions. To make water, HOH, we use 1 H⁺ for every OH^-. Because they are in equal parts, this means that the number of moles of H⁺= the number of moles of OH^-. So the number of moles of H⁺ ions are the same as the number of moles of OH^-, which is 0.005736 moles.
5. At this step, we have determined the number of moles of H⁺ in solution from the acid HBr. From the equation of HBr, we see that we have one molecule of H⁺ for every molecule of acid. This means that the number of moles of H⁺ equals the number of moles of the HBr acid molecules. Now we have the number of moles of the acid, HBr.
6. Finally, to obtain the molarity of HBr, we must divide the number of moles of acid with the volume of the acid. We know that we have 0.005736 moles HBr, and from the problem statement, we know that we have 26.8 mL of acid. After converting the 26.8 mL of acid to units of liters and obtain 0.0268 L of HBr, we can divide the moles of HBr with its volume to determine the molarity of the HBr, as follows: 0.005736 mol HBr/0.0268L HBr = 0.214 mol/L HBr

From these calculations, we determined that the molarity of the acid is 0.214 M.

Answer 2

First, write chemical equation:

2 HBr + Ba(OH)2= BaBr2+ 2H2O

as we can see, acid react with base in ratio 2:1

Let's find out, how many mol of base is in 24, 1 mL or 0.024 L solution:

0..024 L x 0.119 L/mol = 0.003 mol

Now, we are looking for, how many mol of HBr react with the base

2 mol x 0.003 mol= 0.006 mol HBr

so, in 26, 8 ml or 0.027L of solution of acid dissolved 0.006 mol of acid

therefore, in 1 L of solution dissolved 0.22 mol ( 0.006 mol/ 0.027 L) = 0.22 mol/L

M= 022