Topic 8 (Chemical analysis) Flashcards
What is a pure substance in chemistry?
A pure substance is a material that contains only one type of element or compound and has a fixed melting and boiling point.
How can you tell if a substance is pure?
A pure substance will have a sharp, specific melting and boiling point, whereas an impure substance will have a range
What is a formulation?
A formulation is a mixture designed for a specific purpose, made by combining different substances in precise proportions.
Give three examples of formulations.
Paints, medicines, fuels, cosmetics, cleaning agents, alloys.
Why are formulations important in the pharmaceutical industry?
They ensure the correct dosage, effectiveness, and stability of a drug.
How does chromatography help in chemical analysis?
It separates substances in a mixture based on their solubility and allows identification using retention factors.
What is the Rf value in chromatography?
Rf = Distance moved by substance/ distance moved by the solvent
How can chromatography be used to check purity?
A pure substance will produce a single spot, while a mixture will produce multiple spots.
What is the difference between a pure substance and a mixture?
A pure substance has a fixed composition, whereas a mixture contains two or more substances that can be separated.
What happens to the melting point of a substance if it is impure?
The melting point is lower and occurs over a range of temperatures.
What is the purpose of paper chromatography?
To separate substances in a mixture and identify them.
What is the mobile phase in chromatography?
The solvent that moves through the paper, carrying the substances with it.
What is the stationary phase in chromatography?
The chromatography paper, which does not move.
Why do different substances travel different distances in chromatography?
Because they have different solubilities in the solvent and different attractions to the paper.
Why must the baseline in chromatography be drawn in pencil?
Because pencil is insoluble and will not interfere with the results.
What does it mean if two substances have the same Rf value?
They are likely to be the same compound.
Why should the solvent level be below the baseline in chromatography?
To prevent the substances from dissolving into the solvent instead of moving up the paper.
How can chromatography be used to check the purity of a substance?
A pure substance will produce a single spot, whereas a mixture will show multiple spots.
Why is a lid often placed on the beaker during chromatography?
To prevent the solvent from evaporating too quickly and to ensure an even rise of the solvent.
What is the test for hydrogen gas?
Place a lit splint near the gas; if hydrogen is present, it will produce a squeaky pop sound.
What is the test for oxygen gas?
Insert a glowing splint into the gas; if oxygen is present, the splint will relight.
What is the test for carbon dioxide gas?
Bubble the gas through limewater (calcium hydroxide solution); if carbon dioxide is present, the limewater will turn cloudy/milky.
What is the test for chlorine gas?
Hold damp blue litmus paper in the gas; if chlorine is present, the paper will turn red and then be bleached white.
Why does limewater turn cloudy when exposed to carbon dioxide?
Because carbon dioxide reacts with calcium hydroxide to form calcium carbonate, which is an insoluble white precipitate.
