What went wrong when the king rode under the arch?

It was too low and knocked off his crown

How does the chain of blame unfold in the poem?

Each accused person blames another, ending with the king's own changes

State the law of conservation of mass.

Proposed by Lavoisier, it states that matter can neither be created nor destroyed, so there is no net change in mass during a physical or chemical change.

State the law of definite proportions.

Given by Proust, a given compound always contains exactly the same proportion of elements by mass, irrespective of its source.

State the law of multiple proportions.

Given by Dalton, when two elements form more than one compound, the masses of one element combining with a fixed mass of the other are in a ratio of small whole numbers.

State Avogadro's law.

Equal volumes of all gases at the same temperature and pressure contain equal numbers of molecules.

What is the modern standard for atomic masses?

Carbon-12, which is assigned a mass of exactly 12 u; one unified mass unit equals one-twelfth the mass of a \(^{12}\)C atom.

Define molarity and molality.

Molarity is moles of solute per litre of solution; molality is moles of solute per kilogram of solvent and is temperature-independent.

How is mass per cent of an element in a compound found?

By dividing the mass of that element in one mole of the compound by the molar mass and multiplying by 100.

Distinguish precision from accuracy.

Precision is the closeness of repeated measurements to one another, while accuracy is closeness of a measured value to the true value.

How is a molecular formula related to the empirical formula?

Molecular formula equals \(n\) times the empirical formula, where \(n=\) molar mass \(\div\) empirical formula mass.

State the four postulates of Dalton's atomic theory.

Matter consists of indivisible atoms; all atoms of an element are identical in mass and properties; compounds form when atoms combine in fixed whole-number ratios; chemical reactions only rearrange atoms, which are neither created nor destroyed.

Some Basic Concepts of Chemistry

Class 11 Chemistry · Chemistry Part I · Chapter 1

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CBSE Class 11 · Chemistry

Chemistry Part I: 45 of 70 theory marks

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9 marks each: Atom and Thermodynamics
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CBSE Class 11 · Chemistry

Organic basics: 11 marks, the biggest unit

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Summary

Chemistry is the science that studies the preparation, properties, structure and reactions of material substances. Matter — anything that has mass and occupies space — exists in three interconvertible physical states (solid, liquid, gas) and is classified into pure substances (elements and compounds) and mixtures (homogeneous or heterogeneous). Properties may be physical or chemical, and are measured using the SI scheme of seven base units. Because every measurement carries uncertainty, results are expressed using scientific notation \(N\times10^{n}\), significant figures, and the factor-label method of dimensional analysis. Five laws of chemical combination — the law of conservation of mass (Lavoisier), the law of definite proportions (Proust), the law of multiple proportions (Dalton), Gay-Lussac's law of gaseous volumes, and Avogadro's law — led John Dalton to his atomic theory. Atomic masses are referred to the carbon-12 standard, and average atomic mass accounts for isotopic abundance. The mole, containing \(6.022\times10^{23}\) entities, links mass to number of particles; molar mass in grams equals the atomic, molecular or formula mass in unified mass units. Percentage composition yields empirical and molecular formulae, and stoichiometry uses balanced equations, the limiting-reagent idea and concentration terms such as mass per cent, mole fraction, molarity and molality.

Nature and classification of matterProperties of matter and SI unitsUncertainty in measurement and significant figuresLaws of chemical combinationDalton's atomic theoryAtomic and molecular massesMole concept and molar massPercentage composition and formulaeStoichiometry and limiting reagent

Key terms

Matter

Anything that has mass and occupies space; it exists in three physical states — solid, liquid and gas.

Significant figures

The meaningful digits of a measurement that are known with certainty plus one estimated (uncertain) digit.

Mole

The SI unit of amount of substance; one mole contains exactly \(6.022\times10^{23}\) elementary entities (Avogadro number).

Empirical formula

A formula giving the simplest whole-number ratio of the atoms present in a compound.

Limiting reagent

The reactant present in the least relative amount, which is consumed first and limits the quantity of product formed.

Molarity

The number of moles of solute dissolved per litre of solution, \(M=n_{solute}/V_{solution}\).

Extra questions & answers

Try one from this chapter

The law of conservation of mass was proposed by:

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