Why do ionic compounds have high melting points?
Strong electrostatic forces between the ions take a very high amount of thermal energy to separate.
Why can ionic compounds conduct electricity as liquids but not as solids?
When solid, the ions are fixed in a lattice, they cannot move and thus cannot carry charges. The lattice breaks down as a liquid, allowing them to move.
What state symbol is HCl solution?
aq
What determines what cation is the product of electrolysis?
H+ ions turn into hydrogen unless the cation is LESS reactive than it.
How can you tell the moles of a reactant if you know the moles of a product
compare their ratio (e.g 1:1 implies 1 mole of reactant for every mole of that product)
Describe the core practical of investigating pH
Add HCl and Calcium hydroxide at intervals respectively, measuring with a pH indicating tool after each. Compare.
What is the purpose of the fuel burning practical?
To compare the energy released per gram by different fuels through combustion.
What is the key formula used in the fuel burning practical?
Energy = mass of water × 4.2 × temperature change (in Joules).
Why do we use a draught shield in the fuel combustion practical?
To reduce heat loss to the environment and improve accuracy.
Why might experimental values in the combustion practical be lower than expected?
Heat is lost to surroundings, incomplete combustion, or soot forming on the beaker.
What variable must be kept constant when comparing fuels?
Volume of water, distance from flame to beaker, and time the fuel burns.
What safety precaution is vital when using alcohol fuels?
Keep away from open flames; alcohols are highly flammable.
How can you improve accuracy in the combustion core practical?
Use a lid, insulate the beaker, and measure temperature precisely.
What is a hydrocarbon?
A compound made only of hydrogen and carbon atoms.
How does hydrocarbon chain length affect its properties?
Longer chains = higher boiling points, more viscous, less flammable.
What is the general formula for alkanes?
CₙH₂ₙ₊₂
What is a saturated hydrocarbon?
A hydrocarbon with only single bonds (alkanes).
What is the test for alkenes?
Bromine water turns colourless if a C=C double bond is present.
What is cracking and why is it used?
Cracking breaks long alkanes into shorter alkanes and alkenes to meet demand for fuels and feedstocks.
What are the conditions for catalytic cracking?
Heat to ~550°C and use a catalyst like silica or alumina.
What are the products of complete combustion?
Carbon dioxide and water.
What is the danger of incomplete combustion?
It produces carbon monoxide – a toxic gas that prevents oxygen transport in blood.
What gases made up Earth’s early atmosphere?
Mainly CO₂, with little O₂, and small amounts of nitrogen, methane, and ammonia.
How did oxygen levels increase over time?
Photosynthesis by algae and plants.
