Key Concepts in Chemistry EQ Wrongs Flashcards
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)
- 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)
Give the definition of the relative atomic mass of an element (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)
Explain why some elements have relative atomic masses that are not whole numbers (1)
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)
Explain why Mendeleev left gaps in his table (1)
To keep elements with similar properties in the same group (1)
Suggest how you can tell from a dot and cross diagram that the particles in a compound are held together by ionic bonds (1)
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)
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)
- 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
What was the order of discovery of the subatomic particles in the atom? (1)
electron - proton - neutron (1)
Why did Mendeleev leave gaps for undiscovered elements? (1)
So that elements with similar properties could be placed together; [1 mark]
Explain why liquid iodine is unable to conduct electricity (2)
- Iodine has no delocalised / mobile electrons or ions; [1 mark]
- That can carry the charge; [1 mark]
[Total: 2 marks]
State one difference between Mendeleev’s table and the modern periodic table (1)
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]
How do we separate sand from a mixture of sand and sodium chloride solution? (1)
Though Filtration (1)
Why is a condenser used in simple distilation? [2]
- To cool; [1 mark]
- So (water) vapour / gas turns to liquid; [1 mark]
What other equipment can we use in simple distillation rather than a bunsen burner to heat up the flask? [1]
Electric heater / heating mantle / spirit burner / hot plate / blow torch; [1 mark]
Changes in state are physical changes. Explain why they are physical changes rather than chemical changes [2]
- 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]
Why should the thermometer be level with the side arm in simple distillation? [1]
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]
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.
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]
Describe what you would see if damp blue litmus paper was placed in chlorine gas [2]
Blue litmus first turns red; [1 mark]
Allow shades of red and pink
Then bleaches / turns white; [1 mark]
Explain why chlorine is a gas at room temperature rather than a liquid [3]
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]
Describe what is seen when chlorine water is added to potassium iodide solution and the mixture is shaken [2]
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]
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]
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]
Predict what type of bonding would exist in xenon difluoride. Explain your answer [2]
Covalent (bonding); [1 mark]
(Because) they are both non-metals; [1 mark]
Explain why a change in state is a physical change rather than a chemical change? [2]
- 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]
Describe how sedimentation is carried out [2]
- (put waste) water in a tank/ left to (stand/settle) [1]
- {particles / dirt/ impurities/ sediment/ solid} fall to the bottom [1]
State what could be changed in a chromatography experiment to make the Rf value more accurate [1]
- longer paper / {medium paper} [1]
State why waste water is filtered [1]
To remove {insoluble substances/ solids} [1]
Describe what you would see if damp, blue litmus paper is placed into chlorine gas [2]
- blue litmus paper turns red initially [1]
- then bleaches/ turns white [1]
An ionic compound is a giant structure of ions. Describe how it is held together. [3]
- 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).
Explain why chlorine is a gas, rather than a liquid at room temperature [2]
- intermolecular forces between molecules [1]
- take little energy to separate [1]
- boiling point is below room temperature [1]
How did Bohr show that electrons can move. between orbits? [2]
- Move closer to nucleus – Absorb electromagnetic radiation [1]
- Move away from nucleus – Emit electromagnetic radiation [1]
Define a fullerene [2]
- Fullerenes are carbon molecules with a hollow shape (1 mark).
- Fullerenes consist of hexagonal rings of carbon (1 mark).
What is a carbon nanotube? [2]
Cylindrical fullerenes (1 mark) with very high length to diameter ratios (1 mark)
