Elements, Compounds And Mixtures Flashcards
What tells us the element?
The number of protons
What is an element?
A substance formed from one type of atom
(Can’t be split into anything simpler)
What is a compound?
A substance formed from two or more different atoms chemically combined/bonded together
(In fixed proportions)
What is a molecule?
Two or more atoms held together by chemical bonds
—> can’t contain different elements
What does pure mean?
When you have just one element or compound
(No other substance is present)
What does impure mean?
When an element or compound is mixed with small amounts of other substances (impurities)
What is the difference between Co and CO
Co: an element (cobalt)
CO: a compound (carbon monoxide)
Pure substances have a …
Sharp melting/boiling point
What temperature does pure water melt at?
0 degrees celsius
What temperature does pure water boil at?
100 degrees celsius
What happens to the melting point of a substance if an impurity is present?
It decreases and is not sharp
Salty water may start melting at -5 and finish melting at -2
What happens to the boiling point of a substance if an impurity is present?
Increases
Salty water might boil at 103 degrees celsius
How could you confirm whether a substance is pure or impure?
Measure its melting or boiling point
Pure substances have fixed, sharp melting/boiling points
What is a mixture?
Two or more substances not chemically combined together
What can compounds only be separated into elements by?
Chemical changes
Why are mixtures easy to separate using physical processes?
Because they are not chemically combined
What are some separation techniques?
Filtration
Crystallisation
Evaporation
Distillation
Fractional distillation
Chromatography
What is filtration used for?
To separate an insoluble solid from a liquid
- the insoluble solid cannot pass through the filter paper but the liquid molecules can
What equipment is used in filtration?
Conical flask
Filter funnel
Filter paper
Beaker (to hold the mixture before separating)
What is crystallisation used for?
To separate a dissolved solid (soluble solid) from a solution
Steps for crystallisation
1) heat the solution
2) when some of the solvent evaporates and crystals start forming in the solution you stop heating it and leave it to cool
—> more crystals will start to form
3) filter out these crystals from the remaining solution
4) dry these crystals (in a sunny area or a dry oven)
What equipment is used in crystallisation?
Tripod
Gauze
Bunsen burner
Evaporating dish
What is evaporation used for?
To separate a dissolved solid (soluble solid) from a solution
Steps for evaporation
1) heat the solution
2) the solvent will start to evaporate (the remaining solution is more concentrated)
3) crystals will start to form because it is so concentrated
4) eventually all the solvent will evaporate leaving dry crystals of our solid
Pros and cons of evaporation
Pros: quick and easy
Cons: some solids decompose when heated (thermal decomposition)
—> solid will be broken down into something else
What equipment is used in evaporation?
Tripod
Gauze
Bunsen burner
Evaporating dish
What is distillation used for?
To separate a pure liquid from a solution
Steps for distillation
1) heat the solution
2) the pure liquid will boil and evaporate
3) as it rises to the top of the flask the pressure will force it down the condenser
4) the vapour will cool it down and condense into liquid form
5) it will run down the pipe and collect in the beaker
What equipment is used in distillation
Thermometer
Gauze
Tripod
Anti-bumping granules
Bunsen burner
Round-bottom flask
Condenser
Clamp stand
Beaker
What is fractional distillation used for?
To separate a pure liquid from a mixture of liquids
Steps for fractional distillation
1) heat the mixture
2) when temp reaches the boiling point of one of the liquids it will evaporate and rise up the fractionating column
3) it will then pass into the condenser and condense back into the liquid and collect into the beaker
4) repeat for each liquid’s boiling point
What is the fractionating column used for?
To help separate liquids with similar boiling points
What equipment is used in fractional distillation?
Thermometer
Gauze
Tripod
Bunsen burner
Round-bottom flask
Fractionating column
Condenser
Clamp stand
Beakers
What is chromatography used for?
To separate a mixture of different dyes in an ink (or dissolved substances)
Chromatography results
1) each substance will travel a different distance up the paper depending on how soluble it is in the solvent
2) the most soluble substances travel the furthest
What is the stationary phase?
The paper that the substances move on
Molecules can’t move
What is the mobile phase?
The liquid (solvent) that moves through the paper carrying the substances
Molecules can move
In chromatography what depends on how far each of the substances travel?
Their properties
What equipment is used in chromatography?
Lid
Beaker
Filter/chromatography paper
Equation for Rf value
Distance travelled by the spot
——————————————
Distance travelled by the solvent
What does it mean if two sports have the same Rf value?
They are probably the same chemical
What will a pure substance do on a chromatogram?
It won’t separate at all
(Stay a single spot)
What would happen if your repeated the chromatography experiment but with a different solvent or paper?
The chromatogram might look different
—> Rf value would be different too because we would have changed the stationary or mobile phase
What are correctly calculated Rf values always between?
0.00 and 1.00
What is one safety precaution you should take when carrying out the method to separate a soluble solid from a solution (evaporation/crystallisation)
Do not allow it to boil dry
What are anti-bumping granules?
Small glass granules added to a liquid to help it boil smoothly during distillation
What temperature does steam condense at?
100 degrees celsius
What is the name to the solid that collects in the filter paper?
Residue
What is the name given to the liquid that passes through a filter paper?
Filtrate
What term describes the highest point reached by the solvent on a chromatogram?
Solvent front
What should you use for drawing the baseline on a chromatogram?
Pencil
Graphite is insoluble solid won’t run up the paper and interfere with the results
How deep into the solvent should you place the paper when starting a chromatography experiment?
The bottom of the paper must be under the solvent but the baseline and spots must be above the solvent
