Chemistry - separation Flashcards
What are the 4 methods of separating mixtures by physical methods (physical methods means there are physical changes involved)?
Filtration
Evaporation
Chromatography
Distillation
What methods are used for the separation of rock salt?
Filtration and evaporation
What is rock salt?
A mixture of salt and sand
In the experiment to separate rock salt you first of all grind it up in a pestle and mortar, what does this do?
This mixes the different solids together and releases all the salt from rocks
Salt is mined in the form of rock salt
When you dissolve the mixture (rock salt) in water by stirring, what happens?
The salt dissolves into the water however the sand doesn’t dissolve and the sand is left at the bottom.
This difference allows us to separate them.
Is sand soluble or insoluble?
Insoluble
After dissolving, the next stage in separating rock salt is filtration, what is collected where?
The salt dissolved in the water passes through however the sand doesn’t pass through and stays in the filter paper
Does the filter paper have holes in it?
Ye tiny holes you can’t see, the holes are too small to let the sand through
How do you get the salt out of the solution?
You heat from below the mixture (which is in an evaporating dish) to allow evaporation to occur, leaving the salt in the dish
During evaporation,what happens to the water?
It escapes the steam (gas) as the mixture is boiled
What method separates liquids from solids?
Simple distillation
Eg. Salt and water
How do you define a mixture?
2 or more substances jumbled up together
What is the scientific name for a solid that dissolves?
Solute
Eg. In a salt solution the solute is the salt
What is formed when a solute completely dissolves?
Solution
What is the name of the liquid that does the dissolving?
Solvent
Eg. In a salt solution the solvent is the water
If a solute dissolves in a solvent then it is…..?
Soluble
If a solute doesn’t dissolve in a solvent, then it is ……?
Insoluble
Eg. Wax is insoluble in water
If sand can’t dissolve in water it is X in Y?
X is insoluble
Y is water
What is evaporation?
When a liquid changes into a gas
Distillation is the method used to separate a soluble X from a Y?
X is solid
Y is liquid
Condensation is ……
When a gas changes into a liquid
Describe an example (everyday) of condensation?
When liquid drops form on a window, on the inside they have formed from the atmosphere.
In the first step of distillation what is released from the heated flask?
Gas
Eg. If salt and water are the mixture , water vapour is released as gas
How does the gas get to the top of the distillation tube (condenser)?
It rises with the heat
What happens in the condenser (distillation tube)?
Gas is cooling and it turns into a liquid
In a distillation experiment where is the salt near the end?
The salt is left behind in the flask
The water collected is pure or dirty?
Pure because it’s been through the distillation process
What does pure in chemistry mean?
Only contains one substance
Eg. Water only contains H20 molecules
In a distillation experiment a thermometer is at the top of the flask, what temp will it show when water vapour (gas) is released?
100*C
Where water boils
What is chromatography?
It is a separation technique based on the principle, that different substances will take different times to travel through the chromatography paper
Name some uses of chromatography?
To see separation of mixtures
Eg. Dyes in ink, mixtures in blood, food colouring and additives
The distance travelled by a chemical in chromatography is called what?
Retention factor (Rf)
How is the (Rf) calculated?
Ratio of the Distance travelled by the sample spot against the distance travelled by the solvent front
What is the equation for Rf value in chromatography?
Rf = distance moved by spot /
Distance moved by solvent front (liquid line)
What is the base line in chromatography?
It is where the spot is placed (a pencil line can be drawn on the chromatography paper at the start)
The Rf value is always less than 1
T or F?
T
In chromatography experiments, is the base line above the line of liquid at the start?
Yes it’s above the liquid
When the paper is placed in the liquid the liquid solvent moves up through the base line and the substances to be separated move with it
What should the baseline or start line be written in?
Pencil, not ink because it would smudge
What happens to the solvent in chromatography?
It moves up through the chromatography paper
How do you know if different substances are more soluble or less soluble (in chromatography)?
If there’re higher on the paper they are more soluble
What happens when a substance dissolves?
A solute breaks into tiny particles and spreads through out the particles of a solvent
In distillation why is a condenser able to cool a gas as it passes through?
Because it has cold water running on the outside
