Chemistry C8 Flashcards
Difference in melting points between a pure substance and mixtures
pure- melt at its melting point
mixtures- will melt at a range of melting points
What should you use to test for purity?
Crystals
What method is used to separate compounds?
Chromatography
Relative formula mass(Rf) equation
Rf= distance travelled by substance ÷ distance travelled by solvent
Whats tests do you use for the following gases? Hydrogen Oxygen Carbon dioxide Chlorine
Hydrogen=squeaky pop test
Oxygen=relight glowing splint
Carbon dioxide= turns limewater cloudy
Chlorine=bleach damp litmus paper
In chemistry what is a “pure” substance?
A substance made of a single element or compound
How can pure substances be distinguished from impure ones?
By their melting/boiling points
Describe the melting and boiling points of pure substances
One very specific temperature
Describe the melting and boiling points of impure substances
They change state over a temperature range
How does adding an impurity affect the melting an boiling point of a substance?
It lowers the melting point and increases the boiling point
What is a formulation?
A mixture designed as a useful product
Give three examples of formulations
Fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.
What is chromatography?
A process to separate the constituents of a mixture
In paper chromatography, what is the stationary phase and what is the mobile phase?
Paper is stationary, solvent (usually water or ethanol) is mobile
What does the number of spots on a chromatogram tell you about the chemical tested?
The number of spots is the number of compounds in the mixture
How can chromatography show the difference between pure and impure substances?
Pure ones will not separate into a number of spots
How is the Rf value calculated?
Distance moved by spot/distance moved by solvent
What does a substance’s Rf value depend on?
How soluble it is in the solvent
In chromatography, why must the substances be placed on a pencil line?
Pencil will not dissolve in the solvent
In chromatography why must the solvent height be lower than the pencil line?
So that the substances do not dissolve into the solvent off the paper
How can hydrogen be tested for?
Makes a squeaky pop when a splint is placed in it
How can oxygen be tested for?
Relights a glowing splint
How can carbon dioxide be tested for?
Bubble through limewater, turns it milky (cloudy)
Why does carbon dioxide turn limewater cloudy?
Solid calcium carbonate forms
How can chlorine be tested for?
Bleaches damp litmus paper white
