Chemical Analysis Flashcards
What is a pure substance?
A substance with only one element/compound present
Name a characteristic of pure substances
They have a specific melting/boiling point
How can you test is a substance is pure or not?
Boil it. If it has one set boiling point it is pure.
What do impurities do to the melting/boiling point of a substance?
Raise/Lower it. Impure substances will not melt/boil at a set temperature.
What is a formulation?
A mixture that has been designed as a useful product.
What is the equation for percentage composition?
(amount of desired mass / total mass) x 100
In Paper Chromatography, which is the stationary phase?
The paper
In Paper Chromatography which is the mobile phase?
The water
What is phase distribution?
The attraction of the substance to the paper in relation to its attraction to the solvent.
What happens to substances with a stronger attraction to the solvent?
They will travel faster and further up the paper
What happens to substances with a stronger attraction to the paper?
They will move slowly and not very far up
What does the separation of the solute depend on?
The solubility and its attraction to the stationary phase.
What is the Rf value?
The ratio of the distance moved by the substance to the distance moved by the solvent
How do you calculate the Rf value?
Distance moved by substance / Distance moved by solvent
Describe how you would carry out a test for Hydrogen
- Put 5cm depth of HCl into a test tube
- Add a piece of Mg ribbon and seal the test tube with a bung
- Wait for the reaction to happen, you will see fizzing
- Light a splint, remove the bung, then hold the lit splint to the mouth of the test tube.
What is a positive result for a Hydrogen Test?
There will be a squeaky pop if hydrogen is present
Describe how to carry out a test for Oxygen:
- Add 5cm depth of Hydrogen Peroxide into a test tube
- Stand the tube in a rack in the sink
- Add a small amount of manganese dioxide
- Light a splint and tap it gently so it is only glowing
- Hold the splint to the mouth of the test tube and observe the results
What is a positive result of an oxygen test?
The glowing splint should reignite
Describe how to carry out a test for Carbon Dioxide:
- Half fill a test tube with limewater and place it in a test tube rack
- Put the end of a delivery tube in the limewater
- In another test tube add 5cm^3 of HCl and a spatula of Calcium carbonate
- Quickly put a bung in this tube and observe the limewater
What happens to limewater in the presence of CO2
It goes cloudy
Describe how to test for Chlorine:
- Set up an electrolysis cell with aqueous sodium chloride
- Apply current and wait for products to form
- Dip a piece of litmus paper in the solution and observe the results
What is a positive result for a chlorine test?
The solution will bleach the litmus paper
How do you conduct a flame test?
- Dip a piece of platinum wire into the aqueous metal solution
- Hold the piece of wire over a lit bunsen burner and observe the colour of the flame
Why should you use platinum wire rather than a splint for a flame test?
It is unreactive so won’t affect the colour of the flame, whereas a wooden splint will.
