Chemistry

Question 1

what is the purpose of a salt bridge?

Answer 1

1. Prevent direct mixing of the two solutions but allow ions to pass through them and hence complete the circuit
2. Maintain the charge balance (maintain electrical neutrality) in each half-cell.

Question 2

Trend of atomic radius across a period

Answer 2

• NC increases due to increase in number of protons in the nucleus
• Shielding effect remains relatively constant
• Effective NC increases, resulting in an increase in electrostatic forces of attraction btw nucleus and electrons
• valence electrons pulled closer to nucleus

Question 3

Trend in ionic radius period 3

Answer 3

• Na, Mg2, A/ 3+ and P3- , S2, Cl are said to be isoelectronic as they have the same number of electrons, which is 10 and 18 respectively.
• Across the two isoelectronic series (Na* to A/ 3+ and P 3- to C/-), nuclear charge increases and shielding effect remains constant.
• Effective nuclear charge increases and a stronger electrostatic forces of attraction between the valence electrons and the nucleus, hence a decrease in ionic size across each series.
• There is a sharp increase in ionic radii from the cationic series of Na* to A/ 3+ to the anionic series of P 3- to Cl, because the anions has one more quantum shell than the cations.

Question 4

Factors affecting IE

Answer 4

• NC
• number of additional principle quantum shell(shielding effect)
• Location of electron being removed
• Inter electronic repulsion

Question 5

Purpose of topping up with water in every experiment

Answer 5

Keep total volume of reactant mixture constant
To ensure concentration of reactant is proportional to volume of reactant

Question 6

Why only 2 molecules are involved in elementary steps

Answer 6

3 particles colliding with the right orientation and sufficient Ea is a low probability

Question 7

Heterogeneous Catalysis

Answer 7

• Reactant molecules diffuse into the surface of catalyst
• adsorbed onto the active sites
• forms partial bonds with catalyst surface that weakens bonds and lowers Ea
• brings reactants closer and increase collision frequency and hence frequency of effective
• orientated to the correct collision geometry
• after product formed, it is desorbed

Question 8

Property of benzoin acid which allows it to be used in calorimeter

Answer 8

• heat stable
• readily available

Question 9

How is there no heat loss from the calorimeter due to the water jacket

Answer 9

• able to adjust and match the rising temperature within the calorimeter minimising heat loss

Question 10

Why do the ions have different colours

Answer 10

Energy gap between the 2 sets of 3D orbitals after they have split are different hence the absorption of light occurs at different wavelengths