Chemistry ✿ required practicals PAPER 2

Some students investigated the effect of temperature on the rate of reaction.

The students reacted sodium thiosulfate solution with hydrochloric acid.

Describe a method the students should use to produce accurate results [6]

• pour 10cm³ of sodium thiosulfate solution into a conical flask

• add 10cm³ dilute hydrochloric acid into conical flask and place it on a black cross and start a stopwatch

• measure temperature of the solution

• stop stopwatch when cross has disappeared

• measure temperature at the end of the reaction

• repeat experiment at different temperatures

Some students investigated the effect of concentration on the rate of reaction.

A student investigated the reaction between magnesium and hydrochloric acid.
Describe a method the students should use to produce accurate results [6]

• set up a conical flask containing 50cm³ of 1mol/dm³ hydrochloric acid

• have bung and delivery tube attached to gas syringe prepared

• add a 3cm piece of magnesium ribbon

• quickly fit bung on conical flask and start a stopwatch

• record the measurement of gas produced every 10 seconds

• repeat experiment with 2 and 3 mol/dm³ hydrochloric acid

Plan an investigation to determine the Rf value for the dye in this food colouring.

Your plan should include the use of

• a beaker

• a solvent

• chromatography paper

• draw pencil start line on chromatography paper

• using a capillary tube, add a dot of the 4 known inks and the unknown substance

• add water inside a beaker, make sure it isn’t too much that the pencil line is under the water

• attach a glass rod to the filter paper using tape and lower it in the beaker, making sure the sides do not touch the walls

• add a lid onto the beaker

• after 30 minutes remove the chromatogram, let it dry and take measurements needed to calculate the Rf values using the equation

Describe a method to determine the mass of dissolved solids in a 100 cm³ sample of river water [4]

• weigh evaporating dish using scale

• measure 100cm³ of river water using measuring tube and pour water into evaporating dish

• use Bunsen burner to evaporate water until dry

• weigh evaporating dish again with remaining soils

Explain how paper chromatography separates substances. [2]

• solvent moves through paper

• and carries substances different distances

• due to their attraction for paper and solvent

random errors

uncontrollable changes in an experiment

systematic errors

faulty equipment or method

zero error

when scale is not set to zero properly

what is the independent variable in chromatography?

solvent (water)

what is the dependent variable in chromatography?

solubility of dyes/ inks

what are 2 control variables in chromatography?

amount of solvent

temperature of solvent