A sample of potassium hydrogen phthalate (KHC_8H_4O_4), which is an acid, with a

Question

A sample of potassium hydrogen phthalate (KHC_8H_4O_4), which is an acid, with a mass of 0.6204 g is dissolved in water and used to standardize a solution of cesium hydroxide. An endpoint is reached when 22.56 mL of cesium hydroxide has been added. Determine the molarity (in mol/L) of the cesium hydroxide solution. Report your answer to four significant figures. The standardized cesium hydroxide solution is then used to titrate 23.74 mL of a solution of propanoic acid (C_2H_5COOH). An endpoint is reached when 33.22 mL of cesium hydroxide has been added. Determine the molarity (in mol/L) of the propanoic acid solution. Report your answer to four significant figures.

Explanation / Answer

1)

we know that

moles = mass / molar mass

also

molar mass of KHC8H404 = 204 g/mol

so

moles of KHC8H404 = 0.6204 / 204

moles of KHC8H404 = 3.04 x 10-3

now

at the end point

Moles of acid = moles of base

so

moles of KHc8H404 = moles of CsOH

so

moles of CsOH = 3.04 x 10-3

now

molarity = moles / volume (L)

given

volume = 22.56 x 10-3 L

so

molarity of CsOH = 3.04 x 10-3 / 22.56 x 10-3

molarity of CsOH = 0.135

so

the molarity of cesium hydroxide is 0.135 M

2)

we know that

at end point

moles of acid = moles of base

aslo

moles = molarity x volume

so

Ma x Va = Mb x Vb

Ma x 23.74 = 0.135 x 33.22

Ma = 0.189

so

the molarity of propanoic acid is 0.189 M

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