The concentration of a sodium hydroxide (NaOH) solution was found by titration with a 0.10 M hydrochloric acid (HCl) solution using an indicator to identify the end point - Leaving Cert Chemistry - Question 2 - 2016

A suitable indicator for this titration is methyl orange or phenolphthalein.

To rinse the burette A:

1. Use deionised (distilled, pure) water to first rinse the burette.
2. Then rinse it with the solution that it will contain during the titration (hydrochloric acid, HCl).

The piece of glassware B used in the titration is a pipette.

To find the concentration of the sodium hydroxide solution:

• First, calculate the moles of acid used: [ n_{HCl} = C \times V = 0.10 , \text{mol/L} \times 0.0225 , \text{L} = 0.00225 , ext{mol} ]
• Since the reaction ratio of HCl to NaOH is 1:1, the moles of NaOH is also 0.00225 mol.
• Next, calculate the concentration of NaOH: [ C_{NaOH} = \frac{n}{V} = \frac{0.00225 , ext{mol}}{0.025 , ext{L}} = 0.09 , ext{mol/L} ]

To obtain pure NaCl:

1. Conduct crystallization: pour the reaction mixture into an evaporating dish to allow evaporation of water.
2. When crystals of NaCl start to form, remove the dish and place it in a cool place.
3. Once crystallization is complete, filter the crystals to separate them from the solution.
4. Rinse the collected crystals with a small amount of distilled water, then dry them in an oven or air dry.

A labelled diagram should include the evaporating dish, filter paper, and crystallization setup.

The colour observed when a sample of sodium chloride salt is held in the centre of a Bunsen burner flame is yellow.