6.1.2

Suitable experimental procedures for measuring rates of reactions.

Experimental Method	Dependent and Independent Variables	Additional Notes	Diagram
Change in volume of gas produced	Independent: time (seconds)  Dependent: volume of gas (cm3)	Gas syringe (appropriate) or displacement of water in an inverted burette/measuring a cylinder (but only for gas with low solubility in water).
Change in mass	Independent: time (seconds) Dependent: mass (g)	Top pan balance however doesn’t work with light weight gases (e.g. hydrogen)
Change in transmission of light: colorimetry/ Spectrophotome-try	Independent:  time (seconds) Dependent: light intensity	Higher the concentration of the coloured compound more light is absorbed thus less is transmitted	 2HI(g) à H2(g) + I2(g) 
Change in concentration measured using titration	Independent: time (seconds) Dependent: concentration	Samples taken from solution. Quenching stops the reaction at the moment it is withdrawn.	H2O2(l) + 2H+(aq) + 2I-(aq) à I2(aq) + 2H2O(l)
Change in concentration measured using conductivity	Independent: time (seconds) Dependent: electrical conductivity	Conductivity meter- electrodes put into solution. Readings converted into concentrations of ions present.	BrO3-(aq)+5Br-(aq)+6H+(aq)à3Br2(aq) +3H2O(l)
Non-continuous methods of detecting change during a reaction: ‘clock reactions’	Independent:  time (seconds) Dependent: observing a change in the reaction (e.g. magnesium ribbon reacting completely)	Where rate of reaction is hard to measure, time is recorded. Reaction must be closely observed.