Key Concepts in Chemistry EQ Wrongs

Question 1

In 1911, Rutherford, Geiger and Marsden carried out the gold foil experiment. They fired positively charged alpha particles at gold foil. They predicted that most of the particles would pass straight through the foil and a few might be deflected slightly. Describe what actually happened during the gold foil experiment and explain why it happened. (4)

Answer 1

• during the gold foil experiment, most of the atoms did pass straight through the foil (1)
• as an atom is mainly ‘empty’ space (1)
• However, a small number of particles were deflected backwards (1)
• because they hit the nucleus (1)

Question 2

Give the definition of the relative atomic mass of an element (2)

Answer 2

• average of the mass of one atom of the element (1)
• compared to 1/12th of the mass of one atom carbon-12 (1)

Question 3

Explain why some elements have relative atomic masses that are not whole numbers (1)

Answer 3

RAM is an average of the mass numbers of all the different isotopes of an element, taking into account the abundance of each one (1)

Question 4

Explain why Mendeleev left gaps in his table (1)

Answer 4

To keep elements with similar properties in the same group (1)

Question 5

Suggest how you can tell from a dot and cross diagram that the particles in a compound are held together by ionic bonds (1)

Answer 5

the particles in the compound are oppositely charged ions/ have opposite charges/ the bond is formed by electrons being transferred from one atom to another (1)

Question 6

Describe the structure of a crystal of sodium chloride. You should state:
- what particles are present in the crystal
- how these particles are aranged
- what holds the particles together (4)

Answer 6

• sodium chloride contains positive sodium ions (1)
• and negative chloride ions (1)
• that are arranged in a regular lattice/ giant ionic lattice (1)
• the oppositely charged ions are held together by electrostatic forces acting in all directions

Question 7

What was the order of discovery of the subatomic particles in the atom? (1)

Answer 7

electron - proton - neutron (1)

Question 8

Why did Mendeleev leave gaps for undiscovered elements? (1)

Answer 8

So that elements with similar properties could be placed together; [1 mark]

Question 9

Explain why liquid iodine is unable to conduct electricity (2)

Answer 9

• Iodine has no delocalised / mobile electrons or ions; [1 mark]
• That can carry the charge; [1 mark]
  [Total: 2 marks]

Question 10

State one difference between Mendeleev’s table and the modern periodic table (1)

Answer 10

Arranged by order of (relative) atomic mass / (in Mendeleev’s early periodic table) gaps / missing elements / fewer elements / noble gases were not present; [1 mark]

Question 10

How do we separate sand from a mixture of sand and sodium chloride solution? (1)

Answer 10

Though Filtration (1)

Question 11

Why is a condenser used in simple distilation? [2]

Answer 11

• To cool; [1 mark]
• So (water) vapour / gas turns to liquid; [1 mark]

Question 12

What other equipment can we use in simple distillation rather than a bunsen burner to heat up the flask? [1]

Answer 12

Electric heater / heating mantle / spirit burner / hot plate / blow torch; [1 mark]

Question 13

Changes in state are physical changes. Explain why they are physical changes rather than chemical changes [2]

Answer 13

• Physical changes do not result in formation of a new substance / chemical change results in formation of a new substance; [1 mark]
• Physical change is easily reversed / chemical change is not easily reversed; [1 mark]

Question 14

Why should the thermometer be level with the side arm in simple distillation? [1]

Answer 14

Measure the temperature of the water vapour / steam / gas entering the condenser
OR
Measure the boiling point of the water vapour / steam / gas
OR
Check that the water vapour / steam / gas is at 100 C
OR
Allow for accurate measurements of the boiling point / the thermometer will not be accurate where it is positioned; [1 mark]

Question 15

A sample of rock salt contains a mixture of sodium chloride and some insoluble substances.
The rock salt is added to water and the mixture stirred.
The mixture is then filtered to obtain a filtrate of sodium chloride solution.
Describe how a sample of pure,dry sodium chloride crystals can be obtained from the filtrate.

Answer 15

A description including any three from:

Heat solution (to concentrate); [1 mark]
Then either:
Leave solution {in warm place / to crystallise}; [1 mark]
Scrape crystals (from container) / pat dry between filter papers; [1 mark]
Or:
Leave solution {to crystallise / to cool}; [1 mark]
Filter off crystals / decant liquid from the crystals / pat dry between filter papers / dry in oven; [1 mark]

Question 16

Describe what you would see if damp blue litmus paper was placed in chlorine gas [2]

Answer 16

Blue litmus first turns red; [1 mark]
Allow shades of red and pink
Then bleaches / turns white; [1 mark]

Question 17

Explain why chlorine is a gas at room temperature rather than a liquid [3]

Answer 17

There are intermolecular forces between molecules; [1 mark]
These need little energy to break / separate; [1 mark]
So the boiling point is below room temperature / it has a low boiling point; [1 mark]

Question 18

Describe what is seen when chlorine water is added to potassium iodide solution and the mixture is shaken [2]

Answer 18

When chlorine water is added to potassium bromide solution and the mixture shaken you would see:
(The potassium bromide solution) which is colourless; [1 mark]
Turns yellow / brown / orange / red; [1 mark]
[Total: 2 marks]

Question 19

Whilst noble gases are unreactive, under certain conditions, some noble gases can form compounds. For example, Xenon can form compounds with oxygen and fluorine, and krypton can form compounds with fluorine.
Suggest why helium and neon cannot undergo such reactions. [2]

Answer 19

Helium and neon cannot undergo such reactions because:

Their electrons are close to the nucleus; [1 mark]
So the electrons are strongly attracted to the nucleus
OR
They cannot easily lose or share their electrons; [1 mark]

Question 20

Predict what type of bonding would exist in xenon difluoride. Explain your answer [2]

Answer 20

Covalent (bonding); [1 mark]
(Because) they are both non-metals; [1 mark]

Question 21

Explain why a change in state is a physical change rather than a chemical change? [2]

Answer 21

• physical changes do not result in the formation of a new substance / chemical changes result in the formation of a new substance [1]
• physical change is easily reversed / chemical change cannot be easily reversed [1]

Question 22

Describe how sedimentation is carried out [2]

Answer 22

• (put waste) water in a tank/ left to (stand/settle) [1]
• {particles / dirt/ impurities/ sediment/ solid} fall to the bottom [1]

Question 23

State what could be changed in a chromatography experiment to make the Rf value more accurate [1]

Answer 23

• longer paper / {medium paper} [1]

Question 24

State why waste water is filtered [1]

Answer 24

To remove {insoluble substances/ solids} [1]

Question 25

Describe what you would see if damp, blue litmus paper is placed into chlorine gas [2]

Answer 25

• blue litmus paper turns red initially [1]
• then bleaches/ turns white [1]

Question 26

An ionic compound is a giant structure of ions. Describe how it is held together. [3]

Answer 26

• Ionic compounds are held together by strong electrostatic forces of attraction (1 mark)
• between oppositely charged ions (1 mark).
• These forces of attraction act in all directions (1 mark).

Question 27

Explain why chlorine is a gas, rather than a liquid at room temperature [2]

Answer 27

• intermolecular forces between molecules [1]
• take little energy to separate [1]
• boiling point is below room temperature [1]

Question 28

How did Bohr show that electrons can move. between orbits? [2]

Answer 28

• Move closer to nucleus – Absorb electromagnetic radiation [1]
• Move away from nucleus – Emit electromagnetic radiation [1]

Question 29

Define a fullerene [2]

Answer 29

• Fullerenes are carbon molecules with a hollow shape (1 mark).
• Fullerenes consist of hexagonal rings of carbon (1 mark).

Question 30

What is a carbon nanotube? [2]

Answer 30

Cylindrical fullerenes (1 mark) with very high length to diameter ratios (1 mark)