States of Matter
What do we call it when a gas turns into a liquid?
condensation
What process would be the best to use to obtain water from an ink-water solution?
distillation
What process would be the best to use to obtain salt from sea water?
Crystallisation / evaporation
In water purification, why is chlorination needed?
Chlorine kills microorganisms in the water
What process would be the best to use to separate sand and water?
Filtration
What do we call the process where substances turn straight from a solid to a gas?
Sublimation
solder has a range of melting points from 183 – 258oC. Is it a mixture or a pure substance?
Mixture
What are the two steps carried out during distillation?
Evaporation and condensation
What are the three stages of water purification?
Sedimentation – filtration – chlorination
What is fractional distillation used to separate?
Liquids with different boiling points.
If a substance has a melting point of 68oC and a boiling point of 123oC, what state would it be at 125oC?
Gas
In chromatography, how do you calculate a Rf value?
Distance moved by the dye divided by distance moved by solvent
Give the main hazard involved in carrying out crystallisation in a school laboratory, and give a safety precaution that should be taken to reduce the risk.
Spitting:
wear eye protection to avoid damage to eyes and do not evaporate all of the liquid by heating
Why is drinking water not pure, even after being filtered?
It contains minerals / ions
In chromatography, why might you sometimes get a dot that remains on the pencil line and does not travel up the paper?
It is not soluble in that solvent
What happens to the arrangement of particles as a substance melts?
They go from being closely packed in a regular pattern to a random / irregular pattern, but still closely packed.
Give two differences between mixtures and pure substances:
Pure substances have specific boiling / melting points, mixtures have a range.
A pure substance has a fixed composition, a mixture doesn’t
A mixture contains elements / compounds that are not chemically joined together, so can be separated by physical processes.
In chromatography, why is the line drawn in pencil?
So that it does not get dissolved and carried up the paper by the solvent
In water purification, what happens at the sedimentation stage?
Small particles are allowed to settle out / fall to the bottom of the tank
Why is distillation not used in this country to purify water?
It requires a lot of energy / fuel, which would cost a lot.
What happens to the movement of particles as a substance melts?
In a solid the particles vibrate around a fixed point, as it turns into a liquid the particles are able to flow over each other.
How can you tell the difference between a pure substance and a mixture from a heating curve?
A pure substance will have a single melting point – a horizontal line on the curve.
A mixture will have a range of melting points – the line will not be horizontal
In filtration, what do we call the substance that passes through the filter paper?
Filtrate
Why is tap water not useful when carrying out a chemical analysis.
Chemical analysis detects dissolved salts and tap water contains dissolved salts, which could give incorrect results.
In filtration, what do we call the substance that remains behind on the filter paper?
residue