Question

How to caculate moles of NAOH added and the molarity of unknown acid

Sheets (To be attached to your lab report. Recopy if messy) Data Sheets 1 by Unknown Letter oticMolarity of NaOH (mol/L).o Volume of unknown acid (mL.) A. Initial volume0.5 m Run 1 Run 2 Run 3 NaOH 206 20 64 m 33. 35 w B. Final Volume NaOH NaOH volume added (subtract B - A) Moles NaOH added Analysis: Molarity of unknown acid (assuming the acid is triprotic) Average Run 3 Run 2 Sample Calculation of Molarity of unknown acid:

Answer 1

To calculate the no. of moles of NaOH added is calculated using Molarity formula.

Molarity= no.of moles of solute / Volume of solution

==> no. of moles of NaOH = Molarity * Volume

The given NaOH molarity is 0.1024 M

Run 1: n = 0.1024 * 10.36 = 1.060 moles

Run 2: n = 0.1024 * 12.74 = 1.304 moles

Run 3: n = 0.1024 * 12.90 = 1.320 moles

The concentration of the unknown acid is calculated using the formula.

M₁V₁/n₁ = M₂V₂/n₂

(Acid) = (base)

Since the acid is tripotic, 1 mole of acid consumes 3 moles of base (NaOH)

So, n₁ = 1 and n₂ = 3.

The volume of acid taken is 10.0 ml.= V₁

The concentration of NaOH is 0.1024 M = M₂

Run 1 : M₁= M₂V₂n₁ /n₂ V₁

   M₁= (0.1024 * 10.36 * 1)/ 3 * 10 = 0.0353 M

Run 2 : M₁= M₂V₂n₁ /n₂ V₁

    M₁= (0.1024 * 12.74 * 1)/ 3 * 10 = 0.0434 M

Run 3 : M₁= M₂V₂n₁ /n₂ V₁

    M₁= (0.1024 * 12.90 * 1)/ 3 * 10 = 0.0440 M