Matter, measurement and laws2 concepts
- Element: one kind of atom; compound: fixed mass ratio; mixture: any ratio. Mass is conserved (Lavoisier); a compound's mass ratio is fixed (Proust); and hold 16 and 32 g O per 2 g H (multiple proportions).
- At the same T and P, gases react in simple volume ratios (Gay-Lussac: 2 vol + 1 vol → 2 vol steam) and equal volumes hold equal numbers of molecules (Avogadro). Dalton's theory could not explain the volume law.
- Mass is the amount of matter and never changes; weight is a force. Precision: readings agree with each other; accuracy: they agree with the true value. Kelvin temperatures are never negative.
- Significant figures: non-zero digits and zeros between them count; leading zeros never (0.0052 has 2); trailing zeros only with a decimal point (100 has 1, 100.0 has 4, has 3). Exact counts: unlimited.
- × and ÷: keep the fewest significant figures; + and −: keep the fewest decimal places. Rounding off: a dropped digit above 5 raises the last kept digit; exactly 5 raises it only if it is odd (4.335 → 4.34, 4.345 → 4.34).
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24 more concepts in 5 topics
Atomic mass, mole and molar volume; Percentage composition and formulae; Stoichiometry and limiting reagent; Yield, purity and mixtures; and Concentration terms. Read the first part free. Sign in free with Google to read the rest and download the PDF.
Atomic mass, mole and molar volume4 concepts
- Atomic mass unit and average atomic mass1×
- Mole and Avogadro constant11×
- Molar mass from data7×
- Molar volume of a gas19×
Percentage composition and formulae4 concepts
- Percentage composition5×
- Empirical formula8×
- Molecular formula7×
- Combustion analysis8×
Stoichiometry and limiting reagent6 concepts
- Mole ratio from a balanced equation25×
- Combustion of a hydrocarbon13×
- Gas volumes and pressures in reactions5×
- Limiting reagent20×
- Neutralisation by mole counting14×
- Group counting in organic reactions15×
Yield, purity and mixtures3 concepts
- Percentage yield6×
- Purity of a sample3×
- Mixture problems3×
Concentration terms7 concepts
- Molarity14×
- Molality4×
- Mole fraction6×
- Mass and volume percentage6×
- Parts per million3×
- Conversions using density11×
- Dilution and mixing5×
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