Free Liquids MCQs with Answers

• A. are held in fixed positions in a lattice
• B. are close together but free to slide past one another
• C. are very far apart and move independently
• D. have no kinetic energy at all

Explanation: Intermolecular forces in a liquid are strong enough to keep the molecules in contact, which fixes the volume, but not strong enough to…

• A. molecules at the surface are pulled inwards and sideways only, with no upward pull
• B. the surface molecules move faster than those inside
• C. air presses down on the surface
• D. the liquid evaporates from the surface

Explanation: A molecule inside the liquid is pulled equally in all directions, but one at the surface has no neighbours above it, so the net inward…

• A. increases as the temperature rises
• B. is independent of temperature
• C. decreases as the temperature rises
• D. is a measure of how quickly it evaporates

Explanation: Viscosity is resistance to flow and it depends on the intermolecular forces, so heating a liquid gives the molecules more kinetic energy…

• A. the surface of the liquid contracts
• B. cold air replaces the escaping vapour
• C. the vapour formed is colder than the liquid
• D. the fastest moving molecules escape, lowering the average kinetic energy of those left behind

Explanation: Only molecules with above average kinetic energy can break free from the surface, so the average energy of the remaining liquid falls and…

• A. the liquid has completely evaporated
• B. the vapour is in dynamic equilibrium with the liquid in a closed container
• C. the liquid is boiling in an open vessel
• D. the container is completely empty of air

Explanation: In a closed vessel evaporation and condensation eventually occur at the same rate, and the constant pressure of vapour at that point is…

• A. zero
• B. its surface tension
• C. the external atmospheric pressure
• D. the vapour pressure of water

Explanation: Bubbles of vapour can only form and rise through the bulk of the liquid when the vapour pressure inside them matches the pressure pushing…

• A. Water
• B. Glycerol
• C. Ether
• D. Mercury

Explanation: Ether has weak dispersion forces between its molecules, so a large fraction escape the surface easily and it is highly volatile, which is…

• A. carbon, silicon or sulphur
• B. any halogen
• C. a metal
• D. a small, highly electronegative atom such as fluorine, oxygen or nitrogen

Explanation: The electronegative atom pulls electron density away, leaving the hydrogen nucleus unusually exposed so that it attracts a lone pair on a…

• A. water molecules are hydrogen bonded to one another
• B. water has a larger molar mass
• C. hydrogen sulphide is an ionic compound
• D. water molecules are non polar

Explanation: Extensive hydrogen bonding between water molecules must be overcome before they can escape, so a great deal of energy is needed and water…

• A. the high boiling point of ammonia compared with phosphine
• B. the solubility of ethanol in water
• C. the low density of ice compared with water
• D. the electrical conductivity of molten sodium chloride

Explanation: Molten sodium chloride conducts because it is an ionic compound whose ions become mobile when the lattice melts, and there is no hydrogen…

• A. loses one of its hydrogen atoms
• B. is hydrogen bonded to four others in an open tetrahedral arrangement
• C. moves faster than in the liquid
• D. is compressed closer to its neighbours

Explanation: Every molecule uses its two hydrogens and its two lone pairs, so a rigid open cage with large empty spaces is formed, and this occupies…

• A. 0 degrees Celsius
• B. 100 degrees Celsius
• C. 4 degrees Celsius
• D. minus 4 degrees Celsius

Explanation: Cooling water from room temperature increases density as normal, but below 4 degrees the open hydrogen bonded structure begins to form and…

• A. it is a very light molecule
• B. it is a good electrical conductor
• C. a large amount of energy is used breaking hydrogen bonds before the temperature rises
• D. it has a low boiling point

Explanation: Much of the heat supplied goes into breaking hydrogen bonds rather than into increasing the kinetic energy of the molecules, so the…

• A. the adhesive forces between water and glass are stronger than the cohesive forces within water
• B. the cohesive forces are stronger than the adhesive forces
• C. the air pressure inside the tube is greater
• D. water is denser than glass

Explanation: Water wets glass because it is attracted to the silica surface more strongly than to itself, so it climbs the walls and drags a column up…

• A. molar heat of fusion
• B. molar heat of vaporisation
• C. lattice energy
• D. activation energy

Explanation: Molar heat of vaporisation measures the energy needed to overcome the intermolecular forces completely, so it is large for hydrogen bonded…

• A. decreases
• B. remains constant
• C. increases
• D. first increases and then decreases

Explanation: Higher temperature means a larger fraction of molecules have enough kinetic energy to escape the surface, so more vapour is present at…

• A. Water and petrol
• B. Water and ethanol
• C. Oil and water
• D. Mercury and water

Explanation: Ethanol has a hydroxyl group that hydrogen bonds with water, so the two mix in all proportions, illustrating the rule that like dissolves…

• A. mercury is a metal
• B. mercury evaporates rapidly
• C. cohesive forces between mercury atoms exceed the adhesive forces to glass
• D. glass is polar and mercury is non polar

Explanation: Mercury atoms are held to each other by strong metallic bonding far more strongly than they are attracted to the glass, so the liquid…

• A. lowers the boiling point of water
• B. removes all the air from the vessel
• C. increases the amount of steam produced
• D. raises the boiling point of water above 100 degrees Celsius

Explanation: A liquid boils when its vapour pressure equals the external pressure, so raising that external pressure means a higher temperature is…

• A. Liquids diffuse more slowly than gases
• B. Liquids are almost incompressible
• C. The molecules of a liquid are held in fixed positions
• D. Liquids have a definite volume but no definite shape

Explanation: Molecules in a liquid are in constant random motion and slide freely past one another, which is exactly what allows a liquid to flow and…