C8 - Chemical Analysis Flashcards
(21 cards)
Front
Back
What is a pure substance in chemistry?
A substance made of only one element or compound.
How can you tell if a substance is pure?
It has a fixed, specific melting and boiling point.
What is a formulation?
A mixture designed to produce a useful product with specific properties.
Give an example of a formulation.
Medicines, fuels, paints, cleaning agents.
What is chromatography used for?
To separate mixtures and identify substances in them.
What is the stationary phase in paper chromatography?
The paper.
What is the mobile phase in paper chromatography?
The solvent (e.g. water or ethanol).
Why do substances move different distances in chromatography?
They have different attractions to the stationary and mobile phases.
What is the Rf value?
Rf = Distance moved by substance / Distance moved by solvent.
What is the maximum possible Rf value?
1 (if the substance travels with the solvent front).
How can you identify a substance using chromatography?
Compare its Rf value to known values.
What is a positive test for hydrogen gas?
A lit splint makes a squeaky pop.
What is a positive test for oxygen gas?
A glowing splint relights.
What is a positive test for carbon dioxide?
Limewater turns cloudy.
What is a positive test for chlorine gas?
Damp litmus paper turns white (bleached).
Why must the pencil line be used in chromatography?
Pencil is insoluble and won’t interfere with the results.
Why should the solvent level be below the spots on the chromatography paper?
So the samples don’t dissolve into the solvent directly.
What does it mean if a substance produces one spot on a chromatogram?
It is pure.
What does it mean if a substance produces multiple spots?
It is a mixture.
Why is chromatography useful in chemical analysis?
It helps identify substances based on how they separate and move.
