1) When a sample of oxalic acid (H 2 C 2 O 4 ), which is a diprotic acid, is tit

Question

1) When a sample of oxalic acid (H2C2O4), which is a diprotic acid, is titrated with 0.250 M potassium hydroxide solution, 24.44 mL of the potassium hydroxide solution are required to neutralize the acid. How many grams of oxalic acid where present in the sample?

2 KOH(aq)+ H2C2O4(s)? K2C2O4(aq)+ 2 H2O(l)

Your answer should have 3 significant figures.

2) A sodium sulfate solution is added to a 25.0 mL sample of a solution containing Ba2+ions until no more precipitate formed. The precipitate is collected, dried, and weighed. If 1.54 g of the precipitate are obtained, what is the concentration (in M) of Ba2+ions in the 25.0 mL sample?

Explanation / Answer

(1) 2 KOH(aq) + H2C2O4(s) => K2C2O4(aq) + 2 H2O(l)

Moles of KOH = volume x concentration of KOH

= 24.44/1000 x 0.250 = 0.00611 mol


Moles of H2C2O4 = 1/2 x moles of KOH

= 1/2 x 0.00611 = 0.003055 mol


Mass of H2C2O4 = moles x molar mass of H2C2O4

= 0.003055 x 90.035

= 0.275 g


(2) Ba2+ + Na2SO4 => BaSO4 + 2 Na+

Moles of Ba2+ = moles of BaSO4 = mass/molar mass of BaSO4

= 1.54/233.39 = 0.0065984 mol


Concentration of Ba2+ = moles/volume of Ba2+

= 0.0065984/0.0250

= 0.264 M

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