Core Practical 2: Standard solution and titration

Overview:

Procedure:

A 250cm³ volumetric flask has an accuracy of +- 0.6cm³. Calculate the percentage uncertainty in the volume of the sulfamic acid solution in the volumetric flask

0.6/250 × 100 = 0.24%

Each burette reading is accurate to +- 0.05cm³. Calculate the percentage uncertainty in your first accurate titration.

Remember - you always take two burette readings to find a volume.

0.05/18.7 × 200 = 0.5347…

= 0.53% (2dp)

Why should the pipette be rinsed with the sodium hydroxide solution?

• ensures that the pipette is not contaminated

• any distilled water in the pipette could dilute the sodium hydroxide solution meaning that a decreased number of moles would be added

• so it can’t just be rinsed with distilled water

Why is there no need to dry the conical flask after washing it out between trials?

• any distilled water left in the conical flask would have no effect on the number of moles of NaOH added into the conical flask

Identify another indicator that could be used in this titration and state the colour change that would be seen at the end point.

• phenolpthalein

• colour change from pink to colourless at end point