Chemistry

What is the smallest particle of an element that can exist?

• AA molecule
• BAn atom✓
• CA compound
• DAn electron

Answer: An atom is the smallest particle of an element that retains its chemical identity.

Which subatomic particle has a negative charge?

• AProton
• BNeutron
• CElectron✓
• DNucleus

Answer: Electrons have a charge of −1; protons are +1 and neutrons are neutral.

What is the relative atomic mass roughly equal to?

• ANumber of electrons
• BNumber of protons only
• CProtons plus neutrons✓
• DProtons minus neutrons

Answer: Mass is concentrated in the nucleus, so relative atomic mass ≈ number of protons + neutrons.

Elements in the same group of the periodic table have the same number of:

• ANeutrons
• BOuter-shell (valence) electrons✓
• CProtons
• DEnergy levels

Answer: Group number equals the number of outer-shell electrons, giving similar chemical properties.

What type of bonding occurs between a metal and a non-metal?

• ACovalent
• BMetallic
• CIonic✓
• DHydrogen

Answer: Metals lose electrons and non-metals gain them, forming oppositely charged ions held by ionic bonds.

What is the pH of a neutral solution at 25°C?

• A0
• B7✓
• C10
• D14

Answer: A neutral solution (such as pure water) has a pH of 7. Below 7 is acidic, above 7 is alkaline.

Which gas is produced when an acid reacts with a metal?

• AOxygen
• BCarbon dioxide
• CHydrogen✓
• DChlorine

Answer: Acid + metal → salt + hydrogen. The hydrogen gas gives a squeaky pop with a lit splint.

What is the test for carbon dioxide gas?

• AIt relights a glowing splint
• BIt turns limewater cloudy/milky✓
• CIt gives a squeaky pop
• DIt bleaches damp litmus paper

Answer: Carbon dioxide turns limewater (calcium hydroxide solution) cloudy white.

A reaction that releases energy to the surroundings is described as:

• AEndothermic
• BExothermic✓
• CReversible
• DCatalytic

Answer: Exothermic reactions transfer energy to the surroundings, usually raising the temperature (e.g. combustion).

What does a catalyst do in a chemical reaction?

• AIncreases the yield
• BIs used up during the reaction
• CSpeeds up the reaction without being used up✓
• DLowers the temperature of the products

Answer: A catalyst increases the rate of reaction by lowering the activation energy and is not used up.

Which of these is a pure substance?

• ASea water
• BAir
• CDistilled water✓
• DBrass

Answer: A pure substance contains only one element or compound. Distilled water is pure H₂O; the others are mixtures.

During electrolysis, positive ions move towards which electrode?

• AThe anode (positive electrode)
• BThe cathode (negative electrode)✓
• CNeither electrode
• DBoth equally

Answer: Positive ions (cations) are attracted to the negative cathode, where they gain electrons (reduction).