Gas volumes and concentration
Introduced| English | Meaning |
|---|---|
| molar gas volume/ˈməʊlə ɡæs ˈvɒljuːm/ | The volume occupied by one mole of gas at a specified temperature and pressure. |
| concentration/ˌkɒnsənˈtreɪʃn/ | The amount of a substance per unit volume of a mixture or solution. |
| solute/ˈsɒljuːt/ | A substance dissolved in a solvent to form a solution. |
Moles of gases and solutions
- The mole works for gases and dissolved substances too — with two handy shortcuts.
- These let you count particles by measuring volume instead of mass.
Gas volume and concentration lab
n = V / 24 dm3
Change gas volume and see amount scale at room conditions.
What volume (dm³) does 3 moles of a gas occupy at rtp (1 mole = 24 dm³)?
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volume = 3 × 24 = 72 dm³.
How many moles of gas are in 48 dm³ at rtp?
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moles = 48 ÷ 24 = 2.
At room temperature and pressure, one mole of any gas occupies ______ dm³.
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The molar gas volume at rtp is 24 dm³.
Molar gas volume 摩尔气体体积
- At room temperature and pressure (rtp), one mole of any gas occupies 24 dm³.
- So moles of gas = volume (dm³) ÷ 24.
Worked example. What volume does 2 moles of a gas occupy at rtp? volume = moles × 24 = 2 × 24 = 48 dm³.
Convert between moles and mass, gas volume, concentration 浓度 or number of particles
What is the concentration of 0.5 moles dissolved in 2 dm³ (in mol/dm³)?
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concentration = 0.5 ÷ 2 = 0.25 mol/dm³.
Concentration of solutions
- Concentration = moles ÷ volume (in mol/dm³), where volume is in dm³.
- A more concentrated solution has more moles of solute 溶质 in the same volume.
Before using the concentration formula, a volume in cm³ should be:
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1 dm³ = 1000 cm³.
Working with solutions
- Rearrange: moles = concentration × volume.
- (Remember: 1 dm³ = 1000 cm³, so divide cm³ by 1000 first.)
Watch your units. Concentration uses dm³, but volumes are often measured in cm³. Convert cm³ to dm³ (÷ 1000) before using the formula, or your answer will be 1000× wrong.
You've got it
- at rtp, 1 mole of any gas = 24 dm³; moles = volume ÷ 24
- concentration = moles ÷ volume (mol/dm³)
- convert cm³ → dm³ (÷ 1000) before calculating