C2.1

whats a pure substance

whats a pure substance

one element or compound

how can you use melting points to find pur substance

pure substance has sharp melting point

a impure will melt across a range of temp due to mix of componds

relative atomic mass

avarge mass of an atom compared to 1/12th of carbon-12 atom

relative formula mass

mean masses of formula units compared to 1/12th mas of carbon-12

relative molecular mass

mean mass of a molecule compared to 1/12th of carbon-12

empirical formula

smallest whole number ratio of atoms

molecular formula

actual number of atoms in each element in the compound

alloy

mixture of two or more metals

why alloys instead of metals

made to have more desireable proporties than metals

hrder and stronger cause of different sized atom can slide over each over easliy

formulattion of mnixture

mixture with extact quanitites of different subtances tested for optimum properties

formulation examples

sunscreen medicine perfume

filtration

insouble from a solution

put filter paper in funnel pour mixture through funnel

solute left at top solvent in beaker

crystallisation

soluble salt from solution

heat solution in evap basin

solvent will evap concentrating the solution

one crystals form removefrom the heat and allow to coo

as form crystals because it becomes insoluble in highly contrated solution

simple disstillation

separate one liquid from a m ixture of liquids with different boil points

simple disstillation example

place mixture in flask connect to condenser with beaker at end

cold water should enter condenser

heat flask

lower boiling poiubnt will evap and go into condenser

vapour cools and drips into beaker

fractional distilliation

seperate several diffrent substances for diff boiling points

crude oil seperate hydrocarbons

fractional disstillation practical

pour mixture into flask attach fractionating colum and condenseer

heat flask evap at diff temps

lows boiling point goes first and goes to top of column

others may try to get up but top of of colum is cool so they condense

one first liquid is collected raise temp and repeat

chromatography

separte a mixture of soluble substances

stationary and mobile phase

separationdepends on the distribution ofsubstances between two phase

phases in paper chromatography/ tlc

stationary: paper/thin layer of substance supported on unreactive substance

mobile:solvent

tlc practical

pencil line drawn 2cm from base of stationary

dot of mixture placed on this line

stationaryplaced in beaker with 1cm of solvent

solvent travels up staionary phase mixture dissolved in mobile phase

substance seperate depending on how solube in the solvent

tlc reasons

solvent below pencil line to prevnt it being washed away

pencil insted of ink cause it insouble and wont affect resulst unlike ink

Rf VALUE

retention factor ratio between distance travelled by dissolved substanceand distance travelled by solvent

rf value equation

distance traveled by substance/distance travelled by solvent

gas chromatography

seperate mixtures of volitale liquids

stationary = soild/liquid on solid support

mobile phase = inert carrier gas

gas chromatographuy practical

a gas mobile phase carries substances through a column packed with a soild

substance travel through the coilums at different speeds ans are seperated .the time they take to to dectore is retention time can identifty each substance

chromatography pure and impure

pure one spot on tlc one peak on gas

impure multiple spots