Chemical analysis Flashcards
Pure substance
A single element/ compound
Not mixed with anything else
Pure vs impure substances
Pure = it will melt at a specific point/ boil at a specific point
Whereas impure = melts/boils at a range of temps
How to find if a substance is pure?
Increase the temperature
Record at what point it melts
Record what point it boils
If the temperatures are fixed = pure substance
What do heating graphs for impure substances look like?
When it’s changing state, it’s not at a fixed point.
It may slope upwards showing it’s not at a fixed point
Formulation
Complex mixture that has been designed as a useful product
How do we design formulations and why?
Quantity of each component has been carefully measured
So it has the properties we need
Examples of formulations
Fuels
Cleaning products
Paints
Medicine
Alloy
Fertiliser
Food
Physical separation techniques list
Filtration
Crystallisation
Distillation
Chromatography
What is the use of chromatography?
Allows us to separate substances based on their different solubilities
Ie ink into their different colours
How does chromatography work?
When the solvent travels up the paper
It dissolves the inks, carrying them up the paper
So it separates the colours
Stationary phase of chromatography
The paper because it doesn’t move
What is the mobile phase in chromatography?
The solvent (water) because it moves up the paper
Using chromatography, how do we determine if it’s a pure or impure colour?
A pure compound produces a single spot in all solvents
In an impure compound the compounds separate into different spots depending on the solvent
Do different solvents effect chromatography?
Yes
The positions could be further up or down the paper
Why use pencil in chromatography?
Using pen causes pen ink to move up the paper as well
Why exactly does paper chromatography work?
Because substances with a higher solubility can move further up the paper
And those with lower solubility will not go as high
How can we find out what an unknown chemical is in chromatography?
Do the chromatography of the unknown chemical
Draw the solvent line (where the water got to)
Measure distance from pencil line to the chemical
The measure how far the solvent moved from pencil line
Calculate Rf value and find out what that substance is
How to find Rf value
Distance moved by substance
———————————————
Distance moved by solvent
Problem with the method of finding Rf value
Several substances have same Rf value
Repeat using different solvent to narrow it down further
Newly found substance shave no Rf value to find
Test for hydrogen
Insert a burning splint into bung with hydrogen
Hydrogen will burn and make a pop sound
Test for oxygen
Use a glowing splint
Place it in oxygen and the splint will relight (burst into flames)
What is limewater?
Calcium hydroxide dissolved in water
Testing for carbon dioxide
Put some limewater into pipettes bubble the gas through limewater
Repeat several times = cloudy
Testing for chlorine
Insert damp litmus paper
It will be bleached (white)
