Gas volumes and solutions
Introduced| English | Meaning |
|---|---|
| concentration/ˌkɒnsənˈtreɪʃn/ | The amount of a substance per unit volume of a mixture or solution. |
| titration/taɪˈtreɪʃn/ | A method of finding an unknown concentration by measuring the volume needed to react with a solution of known concentration. |
| solute/ˈsɒljuːt/ | A substance dissolved in a solvent to form a solution. |
| burette/bjʊəˈret/ | A graduated tube with a tap used to deliver accurately measured volumes of liquid. |
| significant figures/sɪɡˈnɪfɪkənt ˈfɪɡəz/ | The meaningful digits in a measured or rounded number, beginning with its first non-zero digit. |
Measuring gases and solutions
- Equal volumes of any gases (same conditions) hold equal numbers of molecules.
- One mole of gas takes a fixed volume at r.t.p.
- For solutions, concentration 浓度 links moles to volume.
Gas volume lab
n = V / 24 dm3
Change gas volume and see moles scale at room conditions.
At room temperature and pressure, one mole of any gas occupies about ______ dm³.
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This is the molar gas volume at rtp (24 dm³ per mole).
Equal volumes of different gases at the same temperature and pressure contain:
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This is Avogadro's law: equal volumes (same conditions) hold equal numbers of molecules, whatever the gas.
Volumes of gases
- At the same temperature and pressure, equal volumes contain equal numbers of molecules.
- At r.t.p., one mole of any gas occupies $24.0\ \text{dm}^3$:
The mole is the hub: convert to mass, particles, gas volume or solution concentration
How many moles are in 48 dm³ of gas at r.t.p.? (1 mole = 24 dm³)
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n = V / 24 = 48 / 24 = 2 mol.
Concentration and titration 滴定
- Concentration $c$ is the moles of solute 溶质 per $\text{dm}^3$ of solution (units $\dfrac{\text{mol}}{\text{dm}^3}$):
- A titration finds an unknown concentration by reacting it with a solution of known concentration.
A burette 滴定管 delivers a measured volume of a known solution to find an unknown concentration.
How many moles of solute are in 250 cm³ of a 0.2 mol/dm³ solution? (250 cm³ = 0.25 dm³)
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n = c × V = 0.2 × 0.25 = 0.05 mol.
Match each formula or term to what it gives.
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Gas volume and solution concentration both convert to moles, the hub of every calculation.
A titration is used to:
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In a titration, a known solution is added until the reaction is complete, revealing the unknown concentration.
25 cm³ (0.025 dm³) of an acid is exactly neutralised by 0.002 mol of alkali in a 1:1 reaction. What is the acid's concentration in mol/dm³?
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The acid is also 0.002 mol; c = n / V = 0.002 / 0.025 = 0.08 mol/dm³.
Significant figures 有效数字
- Give answers to a sensible number of significant figures — usually match the data.
- Don't write more digits than the data supports, and don't round too early.
You've got it
- equal gas volumes (same T, P) = equal numbers of molecules
- at r.t.p. one mole of gas = $24.0\ \text{dm}^3$, so $n = \dfrac{V}{24.0}$
- solutions: $n = c \times V$ ($c$ in $\dfrac{\text{mol}}{\text{dm}^3}$, $V$ in $\text{dm}^3$; $1000\ \text{cm}^3 = 1\ \text{dm}^3$)
- a titration finds an unknown concentration; quote a sensible number of significant figures