Principles of Chemistry
Edexcel IGCSE Chemistry 4CH0 — 1.1 States of Matter — Edexcel Linear - OL (Chemistry) Revision Notes & Topical Questions
5 min read 4 parts Lesson 8 of 25 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Lesson summary
States of matter — solubility practical: use mass measurements from a saturated solution to calculate solubility at a specified temperature. Solubility is the maximum mass of solute that dissolves in a given mass of solvent at a stated temperature.
- constant mass
- 74.50 − 25.00 = 49.50 g
- 37.00 − 25.00 = 12.00 g
- 49.50 − 12.00 = 37.50 g
- Solubility = (mass of dissolved solute ÷ mass of water) × 100
- 32.0 g of potassium chloride per 100 g of water
Part 1 of 4What the practical measures
Solubility
Solubility is the maximum mass of solute that dissolves in a given mass of solvent at a stated temperature. Keep the solution at a constant temperature while preparing a saturated sample because solubility usually changes with temperature.
Constant mass
Weigh an empty evaporating basin, then the basin with a sample of saturated solution. Evaporate the water, cool the basin and weigh the dry solid. Repeat heating, cooling and weighing until two successive masses agree; this is constant mass.
Part 2 of 4Find the three masses
74.50 − 25.00 = 49.50 g
Example measurements
- empty basin = 25.00 g;
- basin plus saturated solution = 74.50 g;
- basin plus dry potassium chloride = 37.00 g.
- The mass of solution is 74.50 − 25.00 = 49.50 g.
37.00 − 25.00 = 12.00 g
The dissolved solute mass is 37.00 − 25.00 = 12.00 g. The water mass is the solution mass minus the solute mass: 49.50 − 12.00 = 37.50 g. Do not use the mass of the entire solution as the solvent mass.
Part 3 of 4Calculate solubility
Calculate solubility
Solubility = (mass of dissolved solute ÷ mass of water) × 100. This gives grams of solute per 100 g of water at the temperature of the saturated solution.
At 30 °C in this example, solubility = (12.00 ÷ 37.50) × 100 = 32.0 g of potassium chloride per 100 g of water. Include the temperature and units in the answer.
Part 4 of 4Mass percentage and reliability
24.2%
The mass percentage of solute in the solution uses the whole solution mass: (12.00 ÷ 49.50) × 100 = 24.2%. This differs from solubility because the denominator is solution mass rather than water mass.
Drying to constant mass confirms that water has been removed. Prevent loss of solid while heating and allow the basin to cool before weighing. These steps improve the accuracy of the solute mass and therefore the calculated solubility.
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