Some Basic Concepts of Chemistry
Class 11 · Chemistry
4 ideas in Class 11 Chemistry, explained in plain words, with games and quizzes to practise.
Laws of Chemical Combination
Part of: Laws, Atoms and the Mole
Mass never appears or vanishes in reactions. Each compound holds fixed element shares, while one pair of elements can form several compounds in small whole-number ratios. Gas volumes join in small whole numbers, and equal volumes hold equal counts of molecules.
Why it matters. These patterns forced the atomic idea into being. Balancing and formula work both lean on them.
Formulas
- Mass of reactants = mass of products.
- Gay-Lussac: gas volumes combine in small whole-number ratios.
Key words
- Conservation of mass
- : Mass never appears or vanishes in reactions.
- Definite proportions
- : Each compound holds fixed element shares.
- Multiple proportions
- : One pair of elements forms compounds in small whole-number ratios.
- Gay-Lussac's law
- : Gas volumes join in small whole numbers.
- Avogadro's law
- : Equal gas volumes hold equal molecule counts at fixed temperature and pressure.
Try it in two minutes
- Weigh steel wool before and after rusting in a closed jar.
- Compare two water samples drop by drop.
- Mix measured gas volumes and note simple ratios.
Try at home. Weigh a burning candle setup to test mass keeping.
Atoms, Molecules and the Mole
Part of: Laws, Atoms and the Mole
Atomic masses scale from carbon-12, averaging isotopes by share. Molecules sum their atoms; salts use formula mass over ion lattices. The mole gathers 6.022 times ten to the power 23 entities, weighing the formula mass in grams.
Why it matters. Moles turn uncountable crowds into weighable grams. Every later calculation spends this exchange.
Formulas
- Moles = mass / molar mass
- Particles = moles x 6.022 x 10^23
Key words
- Atomic mass
- : Mass scaled from carbon-12, averaging isotopes by share.
- Molecular mass
- : The sum of the atomic masses in a molecule.
- Formula mass
- : The sum over an ion lattice with no separate molecules.
- Mole
- : 6.022 times 10 to the power 23 entities.
- Molar mass
- : One mole's mass in grams.
Try it in two minutes
- Weigh 18 g of water and name its moles.
- Split salt versus sugar by formula versus molecule.
- Scale a dozen to a mole in imagination.
Try at home. Count spoons of sugar and estimate molecules.
Percentage, Empirical and Molecular Formulas
Part of: Formulas, Reactions and Solutions
Mass percent divides each element's share by the total. Mole ratios from 100 g reduce to the simplest whole set: the empirical formula. Scaling it by molar mass over empirical mass gives the true molecular formula.
Why it matters. Analysis reports percents; reactions need real formulas. This ladder climbs from one to the other.
Formulas
- Mass percent = element mass x 100 / total mass
- n = molar mass / empirical mass; molecular formula = n x empirical
Key words
- Mass percent
- : Each element's share of the total mass.
- Mole ratio
- : Moles of each element from 100 g of compound.
- Empirical formula
- : The simplest whole-number atom set.
- Molecular formula
- : The true atom counts in a molecule.
Try it in two minutes
- Find water's shares from its molar mass.
- Reduce a mole ratio to smallest wholes.
- Scale empirical to molecular by mass.
Try at home. Work out sugar's percent shares from its formula.
Stoichiometry and Concentration
Part of: Formulas, Reactions and Solutions
Balanced coefficients count molecules, moles, masses and gas volumes at once. The reactant that runs out first caps the product. Solutions measure strength by mass percent, mole fraction, molarity per litre of solution, or molality per kilogram of solvent.
Why it matters. Factories, labs and kitchens all scale recipes this way. Limiting reagents stop waste; molarity speeds solutions.
Formulas
- Molarity = moles / litres of solution
- Molality = moles / kg of solvent
- Dilution: M1 V1 = M2 V2
Key words
- Balanced equation
- : Coefficients counting molecules, moles, masses and gas volumes at once.
- Limiting reagent
- : The reactant running out first, capping the product.
- Molarity
- : Moles per litre of solution.
- Molality
- : Moles per kilogram of solvent.
- Mole fraction
- : One part's moles over total moles.
Try it in two minutes
- Balance propane burning step by step.
- Find which reactant runs out first.
- Dilute a stock to a target strength.
Try at home. Dilute juice concentrate by calculated ratios.
What your child will practise
- Atoms, Molecules and the Mole: Candy Quick Fire (Quick Fire)
- Laws of Chemical Combination: Desert Puzzle (Clue Puzzle)
- Laws of Chemical Combination: Desert Quick Fire (Quick Fire)
- Percentage, Empirical and Molecular Formulas: Space Quick Fire (Quick Fire)
- Stoichiometry and Concentration: Ocean Puzzle (Clue Puzzle)
- Quiz: Atoms, Molecules and the Mole (8 questions)
- Quiz: Laws of Chemical Combination (8 questions)
- Quiz: Percentage, Empirical and Molecular Formulas (8 questions)
- Quiz: Stoichiometry and Concentration (8 questions)