Gas volumes at r.t.p.
Watch the whole lecture free
Make a free account to watch every lecture to the end: 6 worked examples, 7 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
That was the teaching part. The rest of this lecture is free with an account: 6 worked examples, 7 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
No password needed now: we email you a link to set one. Already have an account? Sign in, then come back to this page.
The teaching part (1 min) is free to watch. A free account opens the whole lecture: 6 worked examples, 7 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Weighing a gas is awkward
- The molar volume
- The gas formulae
Read the transcript of the teaching part
Last time
Before we start: last time, in The mole, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Weighing a gas is awkward
Weighing a solid is easy. But gases weigh almost nothing, and they escape from the balance. So chemists measure the volume of a gas instead. And there is a beautiful fact: one mole of any gas has the same volume, whether it is hydrogen or carbon dioxide.
The molar volume
One mole of any gas occupies twenty-four decimetres cubed at room temperature and pressure, written r.t.p. Room temperature is twenty degrees Celsius, and room pressure is one atmosphere. This is true for any gas, because gas particles are so far apart that their size does not matter. In cubic centimetres, that is twenty-four thousand cm³.
The gas formulae
To find the volume, multiply the moles by twenty-four. The answer is in decimetres cubed. To find the moles, divide the volume in decimetres cubed by twenty-four. If the volume is in cubic centimetres, divide by twenty-four thousand instead. To convert, a decimetre cubed is one thousand cubic centimetres.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Moles: volumes of gases at r.t.p. · Gas volumes.
The whole chapter: Stoichiometry, Stoichiometry.
Chapter 3: Stoichiometry
- Relative formula mass 6 min
- Formulae of ionic compounds 6 min
- Writing and balancing equations 7 min
- Ionic equations 7 min
- The mole and the Avogadro constant 6 min
- Moles: amount, mass and molar mass 6 min
- Reacting masses 7 min
- Gas volumes at r.t.p. 7 min
- Concentration and titration calculations 9 min
- Percentage composition by mass 6 min
- Empirical and molecular formulae 7 min
- Water of crystallisation 7 min
Also for IGCSE Chemistry 0620
Which topics come up most in IGCSE Chemistry 0620 past papers, counted from every paper since 2004.