I need help solving this prelab. Name Date Determination of the Molar Mass of an

Question

I need help solving this prelab.

Name Date Determination of the Molar Mass of an Acid by Titration with a Base Prelab 1. Calcula te the mass, in grams, of sodium hydroxide needed to prepare 500 mL of approximately 0.1 M solution. 2. A student titrated a 1.0115 g sample of potassium hydrogen phthalate (HKCs04; 204.2285 g/mol, and more commonly known as KHP) with sodium hydroxide. The initial buret reading was 1.16 mL. The final buret reading was 40.62 mL a) Write a balanced equation for the neutralization of KHP with sodium hydroxide. b) Calculate the molarity of the sodium hydroxide solution. Show proper stoichiometry. 3. The sodium hydroxide solution form the previous problem was used to titrate a 1.2587 g sample of an unknown acid. 25.62 mL of the solution hydroxide was required to reach the equivalence point. The acid is known to react with the sodium hydroxide in a 1:1 mole ratio. Calculate the molar mass of the acid. Show proper stoichiometry. 61

Explanation / Answer

1) 500 ml (0.5 L) of 0.1 M or mol/L of NaOH = 0.5 L x 0.1 mol/L = 0.05 mols

molar mass of NaOH = 23 (Na) + 16 (O) + 1 (H) = 40 gm /mol

we know that, moles = mass / molar mass

or, mass = moles x molar mass = 0.05 moles x 40 gm/mol = 2 gm NaOH required

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