Chemical Analysis Flashcards
Paper 2 - C8
Are pure substances mixed with other substances?
No they aren’t
What type of of melting and boiling point do pure substances have?
Specific fixed boiling and melting points
What type of of melting and boiling point do impure substances have?
They melt and boil over a range of temperatures
What is a formulation?
A complex mixture that has been designed as a useful product.
What are some examples of formulations?
-Fuels
-Cleaning products
-Paints
-Medicines
-Alloys
-Fertilisers
-Food
Why are the quantity of each component carefully measured in a formulation?
It’s so the product has the right properties we need
What does paper chromatography allow us to separate?
Separate substances based on their different solubilities.
Why is the paper called the stationary phase?
Because it does not move
Why is the solvent called the mobile phase?
Because it does move
What will a pure compound produce in paper chromatography?
It will produce a single spot in all solvents.
What will compounds in a mixture produce in paper chromatography?
They may separate into different spots depending on the solvent.
Why do we draw our starting line in pencil?
As if we drew it in pen the ink from the pen would move up the paper with the solvent.
How do we calculate the Rf value of a substance?
Distance moved by substance
——————————————— = Rf
Distance moved by solvent
Why may we need to repeat the chromatography experiment when finding the Rf value of an unknown chemical?
-Several different substances could have the same Rf value. Which means we may have to repeat the experiment using a different solvent.
-If the substance has never been analysed before, then there will not be an Rf value on the database.
How do we test for Hydrogen gas?
-First get a test tube which may contain hydrogen.
-Remove the bung and insert a burning splint.
-If Hydrogen gas is present it will burn rapidly and produce a pop sound.
How do we test for Oxygen gas?
-First get a test tube which may contain oxygen.
-Get a glowing splint and place it into a the test tube of oxygen.
-If oxygen is present the splint relights (bursts into flames).
How do we test for Carbon dioxide?
-First get a test tube which may contain carbon dioxide and get one with limewater.
-Draw some of the gas into a plastic pipette.
-Bubble the gas through the limewater and repeat this several times.
-If carbon dioxide is present the limewater will turn cloudy.
How do we test for Chlorine?
-First get a test tube which may contain chlorine.
-Insert a damp litmus paper into the mouth of the test tube.
-If chlorine is present it will bleach the litmus paper and it will turn white.
(Triple only) What colour flame does Lithium produce?
A Crimson flame
(Triple only) What colour flame does Sodium produce?
A Yellow flame
(Triple only) What colour flame does Potassium produce?
A Lilac flame
(Triple only) What colour flame does Calcium produce?
An Orange-red flame
(Triple only) What colour flame does Copper produce?
A Green flame
(Triple only) What are the problems with flame tests?
-The colour of a flame test can be difficult to distinguish. That is especially true if there is only a low concentration of the metal compound.
-Sometimes a sample contains a mixture of metal ions with can mask the colour of the flame.
