2009 Atoms, Bonds and Groups Jan

Question 1

Isotopes of the same carbon atom have same chemical properties. Explain why.

Answer 1

• Same (number of) electrons (in the outer shell)

Question 2

Describe the bonding and structure in graphite
Explain in terms of bonding and structure, the properties of graphite.
-Good conductor of electricity
-Hardness is soft
-Melting point very high

Answer 2

• Giant covalent (lattice) 
• Made up of layers 
Good conductor -
• It has delocalised electrons 
High melting 
• Strong OR covalent bonds have to be broken
Soft
• Weak intermolecular forces between the layers
• Layers can slide

Question 3

Explain using diagram why ammonia has this shape and has bond angle is 107

Answer 3

Shape:
• Pyramidal
• There are 3 bonded pairs and 1 lone pair
• Lone pairs repel more than bonded pairs

Question 4

State the shape of, and the bond angle in an NH4 ion

Answer 4

• Tetrahedral

* 109.5º

Question 5

Ammonium chloride was solid it did not conduct electricity. When it was dissolved in water and formed a solution it could conduct electricity

Answer 5

• Ions OR electrons cannot move in a solid

* Ions can move OR are mobile in solution

Question 6

What is meant by a salt

Answer 6

• When the H+ in an acid is replaced by a metal ion OR an ammonium ion

Question 7

Why is ammonia acting as the base in this neutralisation

2NH3 + H2SO4 -> (NH4)2SO4

Answer 7

• Accepts a proton OR accepts H+

Question 8

Sea water contains chloride ions. Student added aqueous silver nitrate to sea water. What would he observe

Answer 8

• White precipitate

Question 9

Sea water contains chloride ions. Student added aqueous silver nitrate to sea water. What is the ionic equation

Answer 9

• Ag+(aq) + Cl–(aq) ⎯→ AgCl(s)

Question 10

Sea water contains chloride ions. Student added aqueous silver nitrate to sea water. He then added dilute ammonia to the sample. What would happen

Answer 10

• (Precipitate) dissolves OR disappear

Question 11

One benefit of adding chlorine to water

Answer 11

• Removes or kills bacteria O

* Sterilizes water

Question 12

One possible hazard of adding chlorine to water

Answer 12

• Its toxic

* Could form chlorinated hydrocarbons

Question 13

Chlorine reacts with sodium hydroxide to form bleach. What is the equation

Answer 13

• Cl2 + 2NaOH -> NaClO + NaCl + H2O

Question 14

What does (V) represent in chloric (V) acid

Answer 14

• The oxidation number of chlorine

Question 15

Explain the difference in melting points in Mg and Na
Na 98
Mg 639

Answer 15

• Magnesium ions have a greater charge
• Magnesium has more delocalised electrons
• Magnesium has greater attraction between ions and
electrons OR has stronger metallic bonds

Question 16

Sulfur exists as S8 and Chlorine exists as Cl2. Explain the difference in melting points

Answer 16

• Cl2 OR S8 has intermolecular OR induced dipoles
• S8 has stronger intermolecular forces OR induced dipoles than Cl2
• S8 has more electrons

Question 17

Explain the decrease in the atomic radii across the period from Na to Cl

Answer 17

• Nuclear charge increases
• Shielding remains the same
• Greater attraction

Question 18

The approximate pH of Ba(OH)2

Answer 18

• 715

Question 19

Describe and explain the trend in the reactivity of Group 2 with water

Answer 19

• Reactivity increases (down the group)
• Atomic radii increase
• There is more shielding
• The nuclear attraction decreases
• Easier to remove (outer) electrons