2013 Atoms, Bonds and Groups

Question 1

Define the term relative isotopic mass

Answer 1

• Mass of the isotope compared to 1/12th

* to the mass of an atomof 12C

Question 2

What does •xH2O represent in the formula Al2(SO4)3• XH2O

Answer 2

• (The number of) water(s) of crystallisation

Question 3

A student tests chlorine gas with damp blue litmus paper. The litmus paper first turns a red colour and is then bleached. A reaction takes place between chlorine and water in the damp litmus paper.
Explain why the damp litmus paper turns a red colour as a result of this reaction

Answer 3

• Cl2 +H2O -> HCl+ HClO

* H+ ions are released OR HCl/HClO is acidic

Question 4

Suggest why PH3 has a lower boiling point than NH3

Answer 4

• The intermolecular forces are weaker in PH3

•

Question 5

What is a dative covalent bond

Answer 5

• Both electrons have been donated by one atom

Question 6

Explain why the student might expect the H-N-H bond angle to be larger in H3NBF3 than in NH3

Answer 6

• N in NH3 has three bonding pairs and one lone pair of electrons
• N in H3NBF has four bonding pairs and no lone pairs of electrons
• Lone pair of electrons repels more than bonding pairs

Question 7

Describe and explain the trend in reactivity of Group 2 elements with chlorine as the group is descended

Answer 7

• Reactivity increases down the group
• Atomic radius increases/there are more shells
• There is more shielding
• Nuclear attraction decreases
• Easier to remove outer electrons/ Ionisation energy decreases

Question 8

A student was provided with an aqueous solution of calcium iodide. Wants to show solution contained iodide ions

State the reagent that the student would need to add to the solution of calcium iodide. State second reagent tos show iodide ions are present

Answer 8

• AgNO3 OR silver nitrate

* Concentrated ) concentrated (aqueous) NH3

Question 9

What observation would show that the solution contained iodide ions

Answer 9

• Yellow AND precipitate

Question 10

Explain the trend across Period 2

Answer 10

• Across the period number of protons increases
• Atomic radius decreases
• Outer electrons are attracted more strongly to the nucleus

Question 11

Suggest the ion responsible for bleaching

Answer 11

• ClO-

Question 12

Why Na3PO4 described as a salt of H3PO4

Answer 12

• The hydrogen ions OR H+ of phosphoric

acid) are replaced by sodium ions OR Na

Question 13

The main intermolecular forces present in NH3 and PH3

Answer 13

NH3
• Hydrogen bonding
PH3
• Permanent dipole(–dipole interactions)