Paper 2 (8) Flashcards
Chemical analysis (also known as analytical chemistry) is about:
The instruments and methods we use to separate, identify, and quantify different substances.
In chemistry, a pure substance is a:
Single element or compound that hasn’t been mixed with any other substances
Give an example of a pure substance:
Distilled water
True or false? Pure substances always melt and boil at specific temperatures.
True
Pure water boils at 100°C, and freezes at 0°C.
A student is given an unknown, transparent, colourless liquid.
What 2 tests could be done to see if the liquid is pure water?
Boil it, and see if the boiling point is 100°C
Freeze it, and see if the freezing point is 0°C
A student tests the melting point of a sample of salol. The sample starts melting at 36°C, but it doesn’t melt completely until the temperature is 48°C. Is the sample chemically pure, or impure?
Chemically impure.
Pure substances melt at a specific temperature. As this substance melted over a range of temperatures, it must be impure.
Formulations are ________ that have been prepared using a specific ________.
mixtures
formulas
Formulations are made from ______ amounts of different _________, and each component has a particular _________.
precise
components
function
Give 2 that would require a formulation.
Medicines
Paints
Cleaning agents
Which techniques can be used to separate substances? Give 3
Filtration
Chromatography
Crystallisation
Distillation
If we test a substance for purity by measuring its boiling point, is that a physical test or a chemical test?
Physical
Chromatography is a chemical analysis technique used to ________ substances in a _______.
separate
mixture
What is paper chromatography used for?
To separate a mixtures of soluble substances in liquids
What is the name given for the pencil line in chromatography?
The baseline
Why should we use pencil for the baseline rather than pen?
Pen ink would dissolve in the solvent and move up the paper
Should the baseline be submerged in the solvent?
No
Give 2 solvents commonly used in chromatography.
Ethanol
Water
What is the name of the resulting paper we end up with in chromatography?
A chromatogram
The ‘mobile phase’ refers to the molecules that can move.
Which is the mobile phase in paper chromatography?
The solvent
A substance which is ____ soluble in the mobile phase will spend more time in the mobile phase. This means it will move ______, and travel a _______ distance up the paper.
more
faster
further
The ‘stationary phase’ refers to the molecules that can’t move.
Which is the stationary phase in paper chromatography?
The paper
A substance which is less soluble in the mobile phase will spend more time in the __________ phase, so move ______, and not travel very far up the paper.
stationary
slower
Give the formula to calculate the Rf value:
Distance travelled by the substance / Distance travelled by the solvent
True or false?
The Rf value for a substance is specific to a particular mobile phase (solvent) and stationary phase (paper).
If you change either the mobile or stationary phase, you’ll get a different Rf value.
True
How do you test for chlorine gas?
Expose it to damp blue litmus paper
What happens when damp blue litmus paper is exposed to chlorine gas?
The damp litmus paper turns red, then bleaches white
What 2 safety precautions are required for testing chlorine gas?
Do the experiment in a fume cupboard
Wear a gas mask
How do you test for oxygen gas?
Expose it to a glowing splint
What happens when a glowing splint is exposed to oxygen gas?
The glowing splint will relight
How do you test for hydrogen gas?
Expose it to a lit splint
What happens when hydrogen gas is exposed to a lit splint?
There is a squeaky pop sound
How do you test for carbon dioxide gas?
Bubble it through limewater
What happens when you bubble carbon dioxide gas through limewater?
The limewater turns cloudy
