The three pieces of equipment, A and B, shown are used in volumetric analysis - Leaving Cert Chemistry - Question 2 - 2012

It is advisable to use C, typically a wash bottle, containing distilled water to rinse the interior of the pipette before use. This is to ensure that no contaminants or residual solution affect the accuracy of the measurement. Rinsing ensures that the pipette delivers only the solution to be measured.

For pipette A:

1. Rinse the inside with distilled water to remove any contaminants.
2. Then, rinse the pipette with a small amount of the solution to be measured, allowing it to drain out.
3. Ensure that the last drop of solution is retained.

For burette B:

1. Rinse the inside with distilled water first.
2. Next, rinse the burette with a small amount of the titrant solution, allowing it to flow through the tap to avoid air bubbles.
3. Fill the burette with the titrant and ensure there are no air bubbles in the nozzle.

The last drop of solution must not be blown or shaken out of the pipette because it is calibrated to deliver a specific volume, including this last drop. Blowing it out would result in delivering less than the intended volume, compromising the accuracy of the titration results. The design of the pipette ensures the correct amount is delivered, and omitting the last drop would lead to inconsistencies in measurements.

One other piece of equipment used in carrying out the titrations is a titration flask (often a conical flask) used to hold the reaction mixture.

A suitable indicator for this titration is methyl orange. The colour change at the end point is from yellow (in basic solution) to red (in acidic solution).

Using the titration reaction, we start with the balanced equation:

$ext{HCl} + ext{NaOH} → ext{NaCl} + ext{H}_2 ext{O}$

From the titration:

• Volume of NaOH (V₁) = 25.0 cm³ = 0.025 L
• Volume of HCl (V₂) = 20.0 cm³ = 0.020 L
• Concentration of HCl (C₂) = 0.08 M;

Using the formula for dilution: $C_1V_1 = C_2V_2$

For HCl: $C_1 imes 0.025 = 0.08 imes 0.020$ C_1 = rac{0.08 imes 0.020}{0.025} = 0.064 ext{ M}

Thus, the concentration of the sodium hydroxide solution is 0.064 moles per litre.