Question

If I collect 14 grams of Ba(OH)2 and add it to water, what kind of solution do you expect to be formed (acidic or basic)?

Suppose that I make up a solution that is 750 ml using this barium salt and add it to my buret. I collect 6 grams of a solid material and titrate it against the barium, and I do this a total of 3 times. The volumes of barium containing solution used were: 22.9 ml, 24 ml, and 19.8 ml.

What is the concentration in the buret, and how many moles of your barium salt were delivered in each of the three trials? How many equivalents (reactive components, either acid pieces or base pieces) were present in the three 6 gram samples?

Answer 1

Barium hydroxide is a base, it produces (OH^-) hydroxyl ions in water, so that it is a dibasic base.

Weight of the Ba(OH)2 = 14 g

Molar mass of Barium hydroxide = 171.34 g/mol

Moles of itself = weight /Molecular weight = 14/171.34 = 0.0817 moles

Concentration of solution = no of moles / Volume x 1000

= 0.0817 x 1000 / 750 = 0.109 M

Concentration of hydroxyl ion [OH^-] = 2 x 0.109 M = 0.218 M

Weight of the unknown = 6 g

Trail 1:

Volume of Barium hydroxide consumed = 22.9 ml

Concentration of Basic solution = 0.218 M

No of moles = Molarity x Volume /1000 = 0.218 x 22.9 / 1000

= 0.00498 mole of hydroxyl ions present (each one mole of Barium hydroxide produce two moles of hydroxyl ions, so that the concentration of hydroxyl ions double to the concentration of Barium hydroxide)

Trail 2:

Volume consumed = 24 ml

Hydroxyl ion concentration = 0.218 M

No of moles = M x V / 1000 = 0.218 x24 /1000 = 0.005232 moles

No of moles of unknown = 0.005232 (if it is a mono acidic we need to two equivalents of acid moles to neutralize Barium hydroxide moles)

If it is diacidic we need one equivalent of acid moles to neutralize one mole of Barium hydroxide.

Note : we have standard solution is a dibasic and produces two equivalents of hydroxyl ions.

Trail 3:

Volume consumed = 19.8 mL

Molarity of dibasic solution = 0.218 M

No of moles of hydroxyl ions = 0.218 x 19.8 / 1000 = 0.00432 moles.

These hydroxyl ion moles equal = 2 x moles of Barium hydroxide