CA01 · Quiz — Basic Concepts of Matter

Question 1 of 20

Which of the following is a physical change?

ABurning of paper BRusting of iron CMelting of ice DFermentation of sugar

Melting of ice is a physical change — only the state changes (solid → liquid), no new substance is formed. The chemical composition (H₂O) remains the same and the change is reversible. Burning, rusting, and fermentation are chemical changes — new substances are formed.

Question 2 of 20

The SI unit of amount of substance is:

AGram BKilogram CMole DLitre

The mole (mol) is the SI unit for amount of substance. 1 mole = 6.022 × 10²³ particles (Avogadro's number). The SI base units for mass and volume are kilogram (kg) and cubic metre (m³) respectively.

Question 3 of 20

A mixture of iron filings and sulphur can be separated by:

AFiltration BEvaporation CUsing a magnet DDistillation

Iron is magnetic; sulphur is not. A magnet easily attracts and separates iron filings from sulphur. This works because the mixture is a physical mixture — no chemical bonds have formed between iron and sulphur. If heated, they form iron sulphide (FeS) which cannot be separated this way.

Question 4 of 20

Avogadro's number (6.022 × 10²³) represents the number of:

AAtoms in 1 gram of any element BMolecules in 1 litre of any gas CParticles in 1 mole of any substance DElectrons in 1 mole of hydrogen gas

Avogadro's number (Nₐ = 6.022 × 10²³ mol⁻¹) is the number of constituent particles (atoms, molecules, or ions) in exactly 1 mole of any substance. Example: 1 mole of water contains 6.022 × 10²³ H₂O molecules.

Question 5 of 20

Which law states that matter can neither be created nor destroyed in a chemical reaction?

ALaw of Definite Proportions BLaw of Conservation of Mass CLaw of Multiple Proportions DAvogadro's Law

Law of Conservation of Mass (Lavoisier, 1789): in any chemical reaction, the total mass of reactants equals the total mass of products. Matter is neither created nor destroyed — only rearranged. This is why chemical equations must be balanced.

Question 6 of 20

The law of definite proportions (constant composition) states that:

AElements combine in multiple ratios to form different compounds BA pure chemical compound always contains its elements in fixed ratios by mass CThe mass of a product always equals the mass of the lightest reactant DEqual volumes of gases at same conditions contain equal numbers of atoms

Law of Definite Proportions (Proust, 1799): a pure compound always contains the same elements in the same fixed mass ratio, regardless of its source or method of preparation. Example: water always contains H:O by mass = 1:8, whether from a river or a laboratory.

Question 7 of 20

Which among the following is NOT a characteristic of a pure substance?

AHas a fixed melting point BHas a definite chemical composition CHas a variable boiling point DCannot be separated by physical methods

Pure substances have a FIXED (not variable) boiling point. Variable boiling point is a characteristic of mixtures. A pure substance (element or compound) has: definite composition, fixed melting/boiling points, and cannot be separated by physical means.

Question 8 of 20

Dalton's Law of Multiple Proportions states that:

AEqual volumes of gases contain equal numbers of molecules at the same conditions BMasses of one element combining with a fixed mass of another are in whole-number ratios CAll elements always combine in a 1:1 ratio by mass in any compound DThe total pressure of a gas mixture is the sum of all partial pressures

Law of Multiple Proportions (Dalton): when two elements form more than one compound (e.g., CO and CO₂), the masses of one element (O) combining with a fixed mass of the other (C) are in a simple whole-number ratio. For CO vs CO₂: oxygen ratio = 1:2. This supported the atomic theory.

Question 9 of 20

Which of the following is an example of a heterogeneous mixture?

ASalt dissolved in water BAir (mixture of gases) CSugar solution DSoil

Soil is a heterogeneous mixture — its composition is not uniform throughout; you can see different components (sand, clay, pebbles, organic matter). Salt solution, sugar solution, and air are homogeneous mixtures (solutions/alloys) — uniform composition throughout.

Question 10 of 20

The molar mass of water (H₂O) is:

A16 g/mol B18 g/mol C20 g/mol D34 g/mol

Molar mass of H₂O = (2 × 1) + (1 × 16) = 2 + 16 = 18 g/mol. H has atomic mass 1 g/mol; O has atomic mass 16 g/mol. This means 18 grams of water = 1 mole = 6.022 × 10²³ water molecules.

Question 11 of 20

At STP (Standard Temperature and Pressure), 1 mole of any ideal gas occupies:

A11.2 litres B22.4 litres C44.8 litres D1 litre

At STP (0°C, 1 atm), 1 mole of any ideal gas occupies 22.4 litres (molar volume of a gas). This was derived from Avogadro's law. AFCAT note: at SATP (25°C, 1 bar — new standard), molar volume = 24.8 L, but 22.4 L at STP is still the most commonly tested value.

Question 12 of 20

Which of the following best describes an element?

AA pure substance composed of two or more types of atoms chemically combined BA mixture that can be separated back into parts by physical methods CA pure substance of only one type of atom, not breakable by chemical means DAny substance occurring naturally in the Earth's crust in its pure form

An element is a pure substance consisting of only one type of atom. It cannot be broken down into simpler substances by chemical reactions. Examples: iron (Fe), oxygen (O₂), gold (Au). A compound is made of two or more elements chemically combined.

Question 13 of 20

The empirical formula of a compound gives:

AThe actual number of each type of atom present in one molecule BThe simplest whole-number ratio of atoms of each element in the compound CThe three-dimensional spatial arrangement of atoms within the molecule DThe molecular mass of the compound in grams per mole

The empirical formula shows the simplest whole-number ratio of atoms. Example: glucose (C₆H₁₂O₆) has empirical formula CH₂O. The molecular formula (C₆H₁₂O₆) shows the actual atoms per molecule. Molecular formula = n × empirical formula (n = whole number).

Question 14 of 20

A 10% (w/v) solution of NaCl means:

A10 grams of NaCl in 10 mL of solution B10 grams of NaCl dissolved in enough water C10 moles of NaCl in 100 mL of water D10 grams of NaCl in 90 grams of water

% (w/v) = grams of solute per 100 mL of solution. So 10% w/v NaCl = 10 g NaCl dissolved in enough water to make 100 mL total solution. This is commonly used in medical/hospital settings (e.g., normal saline = 0.9% NaCl).

Question 15 of 20

Which of the following is a compound?

AAir BBrass CCarbon dioxide (CO₂) DOxygen (O₂)

Carbon dioxide (CO₂) is a compound — it consists of two different elements (C and O) chemically bonded together in a fixed ratio. Air is a mixture; Brass is an alloy (mixture); Oxygen (O₂) is an element (diatomic).

Question 16 of 20

The percentage composition of an element in a compound is calculated as:

A(Atomic mass of element / Molecular mass of compound) × 10 B(Mass of element in 1 mole / Molar mass of compound) × 100 C(Number of atoms / Total atoms) × 100 DMolar mass of element × 100

% composition = (mass of element in 1 mole of compound / molar mass of compound) × 100. Example: % of O in H₂O = (16/18) × 100 = 88.9%. This is a fundamental stoichiometry concept tested regularly.

Question 17 of 20

Molarity is defined as:

AMass of solute per litre of solvent BMoles of solute per kilogram of solvent CMoles of solute per litre of solution DMass of solute per 100 g of solution

Molarity (M) = moles of solute / litres of solution. Units: mol/L or M. Example: 1 M NaOH = 1 mole NaOH dissolved in enough water to make 1 litre of solution. Molality = moles per kg of solvent (different — not affected by temperature).

Question 18 of 20

Which of the following statements about compounds is CORRECT?

ACompounds can be separated into their elements by physical methods like filtration BThe properties of a compound closely resemble those of its constituent elements CCompounds have fixed composition; their properties differ from constituent elements DAll chemical compounds are found exclusively in the liquid state

Compounds: fixed composition (definite ratio of elements), properties DIFFER from constituent elements (e.g., water is liquid while H₂ and O₂ are gases at room temperature), can ONLY be separated by chemical methods (not physical). These distinguish compounds from mixtures.

Question 19 of 20

The gram formula mass of CaCO₃ (calcium carbonate) is:

A56 g/mol B84 g/mol C100 g/mol D112 g/mol

Molar mass of CaCO₃ = Ca + C + 3O = 40 + 12 + (3×16) = 40 + 12 + 48 = 100 g/mol. CaCO₃ is limestone/marble. This is a commonly tested compound — remember Ca=40, C=12, O=16.

Question 20 of 20

Which of the following correctly states Avogadro's Law?

AEqual masses of gases at the same T and P contain equal numbers of molecules BEqual volumes of all gases at the same T and P contain equal numbers of molecules CAll gases always occupy the full volume of their container at any pressure DThe pressure of a gas is inversely proportional to its volume at constant T

Avogadro's Law (1811): equal volumes of all gases, measured at the same temperature and pressure, contain equal numbers of molecules. This explains why the molar volume of any ideal gas at STP = 22.4 L. Option D is Boyle's Law.

CA01 — Basic Concepts of Matter