Spinach is a leafy green vegetable - Scottish Highers Chemistry - Question 11 - 2022

The ionic formula of copper(II) ethanoate is [Cu(CH₃COO)₂].

To prepare 250 cm³ of a standard solution of oxalic acid:

1. Accurately weigh the required mass of oxalic acid using an analytical balance. Ensure this mass is enough to achieve the desired molarity in 250 cm³ of solution.
2. Transfer the weighed oxalic acid into a clean beaker.
3. Add a small volume of distilled water to the beaker and stir until the oxalic acid is completely dissolved.
4. Once fully dissolved, transfer the solution to a 250 cm³ volumetric flask. Make sure to use a funnel for accuracy.
5. Rinse the beaker and any stirring rods with distilled water, adding the rinsings to the volumetric flask to ensure all oxalic acid is transferred.
6. Add distilled water to the volumetric flask until the bottom of the meniscus touches the 250 cm³ mark.
7. Stopper the flask and invert it several times to mix thoroughly.

The diagram should illustrate a graduated pipette with a narrow end to ensure accurate measurement of the liquid. The scale markings should be visible along the side of the pipette, ideally showing the meniscus level.

The colour change observed at the end point in this titration would be from pink (in alkaline) to colourless (when it becomes acidic).

The term used to describe titrate volumes within 0.2 cm³ of each other is 'concordant.'

To calculate the concentration of sodium hydroxide (NaOH):

1. The average titration volume of oxalic acid is 26.75 cm³.
2. Moles of oxalic acid = 0.126 mol/l × 0.025 L = 0.00315 moles.
3. According to the reaction equation, 1 mole of oxalic acid reacts with 2 moles of sodium hydroxide.
4. Thus, moles of sodium hydroxide = 2 × 0.00315 = 0.00630 moles.
5. The concentration of sodium hydroxide = moles/volume = 0.00630 moles / 0.02675 L = 0.235 mol/l.