2010 Atoms, Bonds and Groups and Jun

Question 1

State the formulae of two ions released when sulfuric acid is in aqueous solution.

Answer 1

• H+
SO42–
HSO4–
• 
• 
•

Question 2

A student adds a sample of solid potassium carbonate, K2CO3, to an excess of dilute

sulfuric acid.

Describe what the student would see and write the equation for the reaction which takes

place.

Answer 2

bubbling OR gas
produced
K2CO3 dissolves OR disappears OR colourless
solution is formed 
H2SO4 + K2CO3  K2SO4 + CO2 + H2O

Question 3

The student repeated the experiment a further three times, using the same number of

moles of CaCO3, SrCO3 and BaCO3.

What trend in the behaviour of the Group 2 carbonates would be observed by the

student?

Answer 3

The ease of (thermal) decomposition decreases

down the group

Question 4

Name the shape of, and state the bond angles in, a BF3 molecule.
Explain why BF3 has this shape.

Answer 4

Shape: trigonal planar 
Bond angle: 120° 
Explanation:
Pairs of electrons repel (one another equally) 
Boron has 3 bonded pairs (and 0 lone pairs)

Question 5

Nitrogen can also form a fluoride, NF3, which has a permanent dipole.
Explain why NF3 has a permanent dipole.

Answer 5

F is more electronegative than N

Dipoles do not cancel

Question 6

Describe and explain the trend in atomic radii of the elements Li to F across Period 2 of the
Periodic Table.

Answer 6

(As you go across the period)
The atomic radii decreases 
The nuclear charge increases

shielding remains the same 
greater (nuclear) attraction on (outer) electrons /
(outer) shell(s)