Chemistry for nursing entrance exams: practice questions with explanations

1Atoms, ions and isotopes

An atom has a nucleus of protons (+) and neutrons (no charge), surrounded by electrons (−) with almost no mass.

• Atomic number = number of protons. It identifies the element.
• Mass number = protons + neutrons.
• A neutral atom has as many electrons as protons.
• Isotopes have the same protons but different neutrons (carbon-12, carbon-14).
• Ions have gained electrons (negative anions, Cl⁻) or lost them (positive cations, Na⁺).

2The periodic table and bonding

Elements are ordered by atomic number. Groups (columns) share the number of valence electrons and similar properties; periods are rows. Group 1 = alkali metals, group 17 = halogens, group 18 = noble gases (full shells, unreactive).

Metals are on the left: shiny, conductive, they lose electrons. Nonmetals are on the right and gain or share electrons. Across a period atoms get smaller and more electronegative; fluorine is the most electronegative element.

• Ionic bond: a metal gives electrons to a nonmetal (NaCl). High melting points; conducts when dissolved.
• Covalent bond: nonmetals share electron pairs (H₂O, CO₂). Unequal sharing makes it polar.
• Hydrogen bonds: attractions between molecules such as water; they explain water’s high boiling point.

Ionic formulas balance the charges: Ca²⁺ + 2 Cl⁻ → CaCl₂; 2 Al³⁺ + 3 O²⁻ → Al₂O₃.

3States of matter and gases

Solids have a fixed shape and volume; liquids a fixed volume but no fixed shape; gases fill their container. Temperature measures the average kinetic energy of the particles.

Phase changes: melting, freezing, evaporation, condensation, sublimation (solid → gas) and deposition (gas → solid). During a phase change the temperature stays constant.

Gas laws (temperatures in kelvin):

4Solutions, acids and bases

A solution is a solute dissolved in a solvent. Water is polar and dissolves ionic and polar substances; oil (nonpolar) does not mix with it: “like dissolves like”.

The pH scale runs from 0 to 14: below 7 acidic, 7 neutral, above 7 basic. Each unit is a factor of 10, so pH 3 has 100 times more H⁺ than pH 5.

Acid + base → salt + water (neutralisation). Strong acids ionise completely (HCl); weak acids only partly (acetic acid). A buffer resists pH change; the bicarbonate buffer keeps blood near pH 7.4.

5Reactions and stoichiometry

Balance an equation by changing coefficients, never the subscripts, until each element has the same number of atoms on both sides.

• Synthesis: A + B → AB. Decomposition: AB → A + B.
• Single replacement: A + BC → AC + B. Double replacement: AB + CD → AD + CB.
• Combustion: fuel + O₂ → CO₂ + H₂O. Neutralisation: acid + base → salt + water.

One mole is 6.02 × 10²³ particles. Molar mass is the sum of the atomic masses (H₂O = 18 g/mol). The path is mass → moles → mole ratio → moles → mass.

Oxidation is loss of electrons, reduction is gain (OIL RIG). Catalysts speed up reactions without being used up; heat, concentration and surface area also raise the rate.

6How exam questions look

• Easy (key terms and facts): subatomic particles, groups of the periodic table, bond types, states of matter, the pH scale, reaction types.
• Medium (applying the concepts): neutrons from the mass number, ionic formulas, gas behaviour, molarity and dilution, balancing simple equations, molar mass.
• Hard (cases and analysis): balancing combustion equations, grams to grams, limiting reactants, pH and [H⁺], average atomic mass, gas-law calculations and buffers.

Write units at every step; they show whether to multiply or divide.