IB Chemistry SL Paper 3 Question Bank

SECTION A

1.) Physical properties and characteristics of elements vary according to the element’s atomic number.

a.) Give a reason and state which group of elements are most likely to undergo sublimation
Answer:
Group 18 elements because the difference between the melting and boiling points are small. They also have the weakest intermolecular forces so they are more prone to undergo solid to gas phase change.

b.) Describe how the trend of the density varies across period 4 and 5
Answer:
The density increases to a maximum value and then begins to decrease

c.) Explain how the oxidation reaction differs for s-block and d-block metals with respect to their melting points and densities.
Answer:
S block elements with high densities and low melting points oxidize easier whereas, d block elements with low densities and high melting points oxidize easier.

2.) There is a mug made of a lead alloy. The rate of lead dissolving in common beverages with various pH values was analyzed.
a.) The table below shows the data. Identify which experiment has the highest rate of lead dissolving.

Answer:
6 because the rate of lead dissolving is calculated by dividing lead concentration by time and experiment 6 gives the highest rate.

b.) Suggest why the relationship between the time and lead concentration for Cola at 16 degrees celsius is not linear.
Answer:
It is not linear because an equilibrium is being established between the lead in the solution and the alloy mug.

c.) Lead (II) Chloride has very low solubility in water
PbCl2 (s) ⇌ Pb2+ (aq) + 2Cl (aq)
i.) Explain how the chloride ions in beverages affect the lead concentrations
Answer:
Equilibrium is shifted towards the reactants and the concentration of lead ions decreases as it precipitates.

SECTION B – Option A Materials

1.) Lithium has many applications
a.) State the bonding present in lithium hydride molecule and define it
Answer
Ionic bonding – It is when +ve (cations) and -ve (anions) ions are attracted to each other and form a continuous giant ionic lattice.

b.) Lithium is paramagnetic and Lithium hydride is diamagnetic. Outline why with reference to its electron configuration
Answer:
Paramagnetic properties are due to the presence of some unpaired electrons which Lithium has. However, all the electrons present in lithium hydride are paired.

2.) A catalyst is a substance that speeds up a chemical reaction without itself being consumed during the reaction.
a.) There are two kinds; heterogenous and homogenous. Differentiate between the two
Answer:
In a heterogeneous reaction, the catalyst is in a different phase from the reactants. In a homogeneous reaction, the catalyst is in the same phase as the reactants.

b.) Elastomers are used for the tyre treads. Explain how they can increase the traction between the tyre and the road.
Answer:
Elastomers tend to make tyres more flexible as they are loosely cross-linked polymers. The long randomly coiled materials can be stretched easily, but return to their original shapes when the force or stress is removed.

3.) The nematic liquid crystal phase is characterized by molecules that have no positional order but tend to point in the same direction.
a.) Describe the shape of the molecule and the effect that an electric field has on it.
Answer:
The shape of nematic liquid crystals are linear or a rod-like shape. When an electric field acts on the liquid crystal, the directional order increases i.e. the molecules arrange themselves in the same direction.

b.) State where nematic liquid crystals are widely used
Answer:
Liquid Crystal Displays (LCD’s)

c.) Nematics are a type of liquid crystals. Explain the effect of high and low temperatures on the liquid crystal behavior
Answer:
When it is in a very low temperature, the intermolecular forces prevent molecules from moving hence forming solid crystals. When it is in very high temperatures, it disrupts the alignment of the liquid crystal molecule and adapts to the characteristics of a fluid.

4.) Metals are usually extracted from their ores by a number of methods. Electrolysis and reduction with carbon are a few of them.
a.) Once the metal is extracted from its ore, the purity can be assessed using ICP Mass spectrometry. Suggest two advantages of using plasma technology in place of regular mass spectrometry.
Answer:
Plasma technology can detect multiple elements unlike mass spectrometry. They can also detect elements in low concentration.

b.) Outline how metals act as heterogeneous catalysts
Answer:
Reactants adsorb onto the active surface. Once they make contact, the bonds are weakened or broken. As this happens, the activation energy is lowered and the products are desorbed.

c.) Explain why alloys are harder than pure metals
Answer:
An alloy is made up of atoms of different sizes rather than being uniform like pure metals. The smaller or bigger atoms distort the layers of atoms in the pure metal. This means that a greater force is required for the layers to slide over each other. This makes the alloy harder and stronger than the pure metal.

d.) Carbon nanotubes can be formed from carbon monoxide. They’re used to increase the tensile strength of the metal. Write an equation to show the reaction
Answer:
2CO (g) → C (s) + CO2 (g)
Carbon nanotubes is a tube made of carbon with diameters typically measured in nanometers. Therefore, it explains the product of the reaction – Carbon.

5.) Polymers have a wide variety of applications but when it comes to disposing of them, they can be a problem.
a.) Define polymers
Answer:
A polymer is a long-chain molecule that is made up of many repeating units.

b.) A known polymer is the isotactic polychloroethene (PVC). Draw its monomer
Answer:

c.) Incinerating PVC can be harmful to the environment. State a product that is produced as a result of this.
Answer:
Carbon monoxide, Hydrochloric acid, Water, Carbon and dioxins

d.) Plasticizers affect the properties of polymers. Define plasticizers and outline its properties.
Answer:
A plasticizer is an additive that is added to another material to improve the polymers processability, flexibility, and stretchability by modifying the mechanical properties. Plasticizers are generally nonvolatile, high boiling and low molecular weight compounds.

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