Brainlag PlusThe rates required practical by the disappearing cross or by collecting gas, with its variables, results tables, 1000 ÷ time, graphs and conclusions.
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 in Plus.
Screen 1 of 4, free to read.
- 9 exam-style questions, marked as you go, each with a worked solution
- Anything you get wrong is saved to your flashcards