Question

Experiment Quantitative Titration - Part 1: Standardization of Sodium Hydroxide Solution

Concentration of HCL standard solution / mol L^-1 = 0.09745

Volume of HCL solution / mL = 25

Indicator: Bromothymol Blue

Average Volume of NaOH / mL = 24.35

Please find concentration of NaOH / mol^-1

Part 2 - Determination of the concentration of acetic acid

Volume of Acedic Acid Solution / mL = 10

Indicator: Phenolphthalein

Average Volume of NaOH / mL = 30.94

Please find the concentration of Acetic Acid / mol L^-1

Part 3: Lab report questions

1. Why must the funnel be removed from the top of the burette during the titration?

2. Volumetric glassware (pipettes, burettes, volumetric flasks, etc.) is usually designated as “TC at 20⁰C” or “TD at 20⁰C”. What do “TC” and “TD” indicate? What is the difference?

3. For convenience the procedure directs you to use clean and dry beakers to collect the hydrochloric acid and acetic acid. Why? How would you change the procedure so that the beakers did not have to be dry?

4. The beaker used to collect the NaOH in part I only needs to be clean. Why is it unnecessary for the NaOH beaker to be dry?

5. Fatima has been asked to prepare a solution of Mg(ClO₄)₂ with an accurately known concentration. However, she discovers that each time she tries to weigh the Mg(ClO₄)₂ the mass is slightly greater. Explain this observation.

Answer 1

Answer:

Part 1

Concentration of HCl   N₁ = 0.09745 mol / L = 0.09745 M = 0.09745 N [ since for HCl molarity = normality]

Volume of HCl V₁ = 25 mL

Concentration of NaOH = N₂ = ?

Volume of NaOH V₂ = 24.35 mL

The volumetric equation is V₁N₁ = V₂N₂

Therefore N₂ = V₁N₁/V₂ = 25 x 0.09745 / 24.35 = 0.100 N

                                                                     = 0.100 M [since for NaOH normality = molarity]

Thus the concentration of NaOH solution is 0.100 mol / L [ since molarity = mol/L]

Part 2.

Concentration of Acetic acid N₁ = ?

Volume of Acetic acid V₁ = 10 mL

Concentration of NaOH = N₂ = 0.100 N   ( determined in part 1)

Volume of NaOH V₂ = 30.94 mL

The volumetric equation is V₁N₁ = V₂N₂

Therefore N₁ = V₂ N₂ / V₁ = 30.94 x 0.100 / 10 = 0.3094 N

                                                                     = 0.3094 M [since for Acetic acid normality = molarity]

Thus the concentration of Acetic acid solution is 0.3094 mol / L   [ since molarity = mol / L ]

Part 3:

1) The funnel at the top of the burete should be removed during titration because

    it obstruct the flow of burette solution during titration and

    any droplets from the funnel may add to the burette solution causing error.

2) TC means total content

    TD means total deliver, that means the quantity delivered from the glassware excluding any liquid material sticking in the glassware. (example at the tip of pipet )

Whereas TC refers to the quantity mentioned is including everything.

Thus TD = TC + Quantity left over after delivery.

3) The beakers if not dried, the moisture will dilute the solutions received in the beaker.

To avoid this, if the beakers are not dried, then we may rinse the beaker with a small quantity of receiving solution and then receive the full quantity. Thus the dilution problem will get avoided.

4) When we use for the first time it needs to be dry to avoid dilution. but when it is used repeatedly for the same solution it is unnecessary to wash and dry everytime.

5) This is because the salt Mg(ClO₄)₂ is highly deliquescent. Hence it absorbs moisture in a very short span of time increasing the weight.