Retrieval practice

Created by

Shekinah Obare

Cards (89)

In everyday language what is a "pure" substance?
A substance that has had nothing added to it and is in its natural state.
Give an example of a "pure" substance that matches the everyday definition of pure. 
Pure milk.
In chemistry, what is a pure substance?
A single element or compound, not mixed with any other substance.
Why is 100% pure orange juice not a chemically pure substance?
It is a mixture of elements and compounds
How can pure substances be distinguished from impure ones?
By measuring their melting/boiling points and comparing to known values.
Describe the melting and boiling points of pure substances.
One specific temperature.
Describe the melting points of an impure substance.  
Lower than the pure substance and has a range.
Describe the boiling point of an impure substance.
Higher than the pure substance and has a range
What is a formulation?
A useful product that is a complex mixture where each chemical in the mixture has a specific purpose and is present in precisely measured amounts.
How are formulations made?
Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties.
Name 6 formulations.
Fuels, cleaning agents, paints, medicines, alloys, fertilisers and processed foods.
How can you spot a formulation in an exam question?
Because a table of ingredients with specific measured amounts of each is given.
What is chromatography?
Separation of mixtures to identify their components.
Chromatography involves interactions between two phases, name them.
Stationary phase and mobile phase.
In paper chromatography (TLC) what is the stationary phase?
The chromatography paper
In paper chromatography (TLC) what is the mobile phase?
The solvent.
Describe how chromatography works.
The solvent moves through the paper. Different compounds have different solubilities in the solvent and different attractions to the paper. Different compounds are carried different distances.
What is the equation for calculating Rf?
Rf = distance moved by solvent / distance moved by spot
What does a substance's Rf value depend on?
How soluble it is in the solvent.
How is distance to solvent front measured?
From the base line to the solvent front.
How is distance to spot measured?
From the base line to the centre of the spot.
How can chromatography tell you the identity of a compound?
Different compounds have different Rf values in different solvents.
How can chromatography test purity of a compound?
A pure compound produces one spot in any solvent but mixtures separate into different spots depending on the solvent.
When running a chromatography, why must the base line be drawn in pencil?
Because ink would run up the chromatography paper.
When running a chromatography, why must the compounds be soluble in the solvent?
So the compounds can move up the paper and separate.
Why is a lid used in chromatography?
To prevent the solvent evaporating away.
Why must the solvent level be below the base line in chromatography?
To prevent the compounds dissolving into the solvent instead of moving up the paper.
Describe the test for hydrogen gas.
Ignite the gas with a lit splint.
Describe the observation for the hydrogen gas test.
A squeaky pop.
Describe the test for oxygen gas.
Place a glowing splint into the gas.
Describe the observation for the oxygen gas test.
The glowing splint relights.
Describe the test for carbon dioxide gas.
Bubble the gas through limewater.
Describe the observation for the carbon dioxide gas test.
Limewater turns cloudy.
What is the chemical name for limewater?
Calcium hydroxide.
Describe the test for chlorine gas.
Add damp litmus paper to the gas.
Describe the observation for the chlorine gas test.
Damp litmus turns white in colour
Name two tests for positive ions.
Flame test and NaOH test.
Describe the steps needed to carry out a flame test.
Clean a nichrome wire loop in acid and hold in a blue Bunsen flame. Dip the wire into the compound and place back in the flame. Record the colour observed.
Which 5 ions are identified using a flame test?
Li+, Na+, K+, Ca2+, Cu2
Which ion produces a crimson flame?
Li+