IB Chemistry HL Paper 1 Question Bank

1.) How do the following properties change down Group 16 of the periodic table?

A.) Atomic radius increases, Ionic radius decreases
B.) Atomic radius increases, Ionic radius increases
C.) Atomic radius decreases, Ionic radius increases
D.) Atomic radius decreases, Ionic radius decreases

Answer: B
The atomic and ionic radii increase down the group. This is due to the addition of a new shell at each successive element on moving down the group.

2.) Which series represents atoms in order of increasing atomic radius?

A.) K < Na < Si
B.) Si < Na < K
C.) Na < Si < K
D.) K < Si < Na

Answer: B
The atomic size increases down the group. Na and K belong to the same group. Hence Na<K. Also atomic size decreases along a period and Na and Si belong to the same period. ∴ Na>Si. On combining, the final order is Si<Na<K

3.) How does a sodium atom form the most stable ion?

A.) Atom gains an electron to form a negative ion
B.) Atom loses electron to form a positive ion
C.) Atom loses proton to form a negative ion
D.) Atom gains proton to form a positive ion

Answer: B
The most stable form of the sodium atom is Na+ and for it to come to this stable state, it needs to lose an electron from its outermost shell. Atoms do not lose protons to become ions as they are present inside the nucleus.

4.) Which of these statements are properties of transition metals?

A.) High melting points
B.) Low densities
C.) Insulators of heat and electricity
D.) Soft in nature

Answer: D
Transition metals are known for having high melting points in addition to high densities, electrical and heat conductivity, variable oxidation states and their ability to form coloured compounds.

5.) How many sigma (σ) and pi (π) bonds are present in ethyne, C2H2?

A.) Sigma bonds: 2 Pi bonds: 2
B.) Sigma bonds: 2 Pi bonds: 3
C.) Sigma bonds: 3 Pi bonds: 2
D.) Sigma bonds: 3 Pi bonds: 3

Answer: C
Each atom is connected by at least one single bond which will be counted as σ bonds and the rest are π bonds. Hence there are 3 sigma (σ) bonds and 2 pi (π) bonds in ethyne.

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6.) Which statement is correct about a catalyst?

A.) Catalysts initiate reactions
B.) Catalysts increase the activation energy
C.) Catalysts increases the yield of the reaction
D.) Catalysts increase the rate of the reaction

Answer: D
Catalysts only increase the rate of the reaction by lowering the activation energy. They do not have the properties of increasing the yield of the reaction or initiating reactions.

7.) Which species has a square planar molecular geometry?

A.) CH2O
B.) CH4
C.) C2H4
D.) CH4O

Answer: B
CH4O is the only molecule that has a hydrogen bonding between O and H. The other molecules have bonds between C and H which are not considered hydrogen bonds. Hydrogen bonds results from the attractive force between a hydrogen atom covalently bonded to a very electronegative atom such as a N, O, or F atom

8.) Which compound makes unpolluted rain acidic in nature?

A.) Nitrogen oxides
B.) Sulfur dioxide
C.) Carbon dioxide
D.) Methane

Answer: C
Unpolluted rain has a slightly acidic pH of 5.6, because carbon dioxide and water in the air react together to form carbonic acid, a weak acid.

9.) Which of the following compounds is polar?

A.) Cl2
B.) CO2
C.) CH4
D.) H2O

Answer: A
Water (H2O) is polar because of the bent shape of the molecule. The shape means most of the negative charge from the oxygen on one side of the molecule and the positive charge of the hydrogen atoms is on the other side of the molecule.

10.) Which of the following increases the rate of reaction?

A.) Decreasing temperature
B.) Increasing concentration
C.) Adding a catalyst
D.) Decreasing collision frequency

Answer: B
With an increase in concentration, the number of molecules with the minimum required energy will increase, and therefore the rate of the reaction will increase. Adding a catalyst, decreasing the temperature and collision frequency will reduce the activation energy.

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