Pure Substances
Define what a pure substance is in chemistry
A single element or compound not mixed with any other substance
What is a formulation?
A formulation is a mixture that has been designed as a useful product
How can you tell from a chromatogram how many substances were present in the mixture
Count the number of spots made from the original mixture
A glowing splint is placed in a test tube of gas and the splint reignites. What gas is it?
Oxygen
DOUBLE JEOPARDY
What is a solvent?
Something that is able to dissolve other substances
Which of these is not a pure substance?
iron pan, carbon dioxide, 100% orange juice
'100% orange juice'
DOUBLE JEOPARDY
Give one example of a formulation
Any from - fuels, foods, cleaning agents, paints, medicines, alloys
Mobile - Solvent (water or ethanol)
A gas is tested with a burning splint and produces a squeaky pop. What gas is it?
Hydrogen - Hydrogen is flammable, so it produces a squeaky pop when tested with a burning splint.
In chromatography, why must the substances be placed on the pencil line?
Pencil will not dissolve in the solvent
How can pure substances be distinguished from impure substances?
By their melting/boiling points
What formulation can be used to make jewellery and why?
How do you calculate an Rf value?
distance moved by substance / distance moved by solvent
DOUBLE JEOPARDY
Which gas causes damp blue litmus paper to turn white?
Chlorine bleaches blue litmus paper, turning it white.
TRUE OR FALSE - If a chemical is very soluble, it won't move.
False - the more soluble something is the further it will move on the chromatography paper.
What would the melting point look like on a graph of an impure substance?
An impure substance would have a range of melting points so would have a sloped line
Emulsions are made from oil, water and an emulsifier. What does the emulsifier do?
Helps mix ingredients together.
Example - oil and water in mayonnaise is emulsified by egg yolk
Substance A has an Rf value of 0.38 cm and Substance B has an Rf value of 0.46 cm. Which substance is more soluble?
The presence of this gas causes limewater to turn milky/cloudy
Carbon dioxide
Why does adding salt to water affect its melting point?
The salt disrupts the bonding in water – meaning the melting point is lowered