The rates required practical by the disappearing cross or by collecting gas, with its variables, results tables, 1000 ÷ time, graphs and conclusions.
What you will learn
- Describe the disappearing cross and gas collection methods
- Name the independent, dependent and control variables
- Work out rate as 1000 ÷ time, means and uncertainties
- Plot rate against concentration and draw a conclusion
Two methods
Disappearing cross. Sodium thiosulfate reacts with hydrochloric acid to make a yellow-white precipitate of sulfur, which slowly hides a cross drawn under the flask.
- Stand a conical flask on a paper cross; add the sodium thiosulfate solution
- Add the acid and start the stopwatch at the same moment
- Look down through the solution; stop the clock when the cross vanishes
- Repeat with other concentrations, keeping the total volume the same
Gas collection. Magnesium ribbon reacts with hydrochloric acid. Put the bung joined to a gas syringe in straight away, then read the volume every 10 s (or time how long it takes to collect a set volume).
The rest of this lesson and its 9 practice questions are locked.
In this lesson
- Two methods
- Variables and fair testing
- From times to rates
- Try it: Work out the rates
9 practice questions, marked as you go; about 25 minutes in all.
Key terms
Disappearing cross, Gas collection, Independent, Dependent, Control, Directly proportional
In this unit: Rates of reaction and equilibrium
Measuring and graphing rates, collision theory and the factors that change a rate, the rates required practical, reversible reactions and how conditions move an equilibrium.