Chem J Flashcards
What is chromatography?
Paper chromatography is used to separate mixtures of soluble substances. These are often coloured substances such as food colourings, inks, dyes or plant pigments.
How do you set up the chromatography practical?
- draw a pencil line on a piece of paper and dot ink across the line.
- lower the paper into the solvent, and watch as the dye spreads up the paper.
- the paper has absorbed the solvent, and the dye has spread further up the paper
what is the Rf (retention factor) value?
the retention factor is a ratio between the distance travelled by the solvent and the distance travelled by a compound.
how do you calcuate the Rf value?
Rf= distance moved by substance
/ distanced moved by solvent
what is the stationary phase?
where particles cant move
What is the mobile phase?
where particles can move
what is a chemically pure substance?
contains only one element or compound and they only boil/ melt at a very specific temperature.
how can hydrogen gas be identifed?
by placing a burning splint into a test tube of gas. Hydrogen burns rapidly with a pop sound.
how can oxygen be identified?
placing a glowing splint into a tets tube of gas. The splint will relight if oxygen is present
how can carbon dioxide be identified?
Carbon dioxide reacts with calcium hydroxide solution to produce a white precipitate of calcium carbonate.
Limewater is a solution of calcium hydroxide. If carbon dioxide is bubbled through limewater, the limewater turns milky or cloudy white.
how can chlorine be identified?
by placing damp litmus paper on to the gas. Chlorine bleaches the paper white.
what is a formulation?
they are mixtures made using a precise amount of each substance, so they can serve a particular purpose.
what colour does potassium turn under the flame test?
purple
what colour does sodium turn under the flame test?
yellow
what colour does lithium turn under the flame test?
red
