Topic 8: Chemical Analysis Flashcards
(38 cards)
In chemistry, what is a pure substance?
Something that contains only one type of compound or element
What is true of the melting and boiling points of a chemically pure substance?
It will melt and boil at a specific temperature
How could you identify the purity of a sample? [2]
- Measure its melting and boiling point and compare it with that of a pure substance (in a data book)
- The closer the measured value is to the actual melting or boiling point, the purer your sample is
What is true of an impure sample? [3]
- Will melt and boil over a range of temperatures
- Melting point will decrease
- Boiling point will increase
What is a formulation? [2]
A useful mixture with a precise purpose [1] which’s components have been measured carefully to ensure it meets its required function [1]
Examples of formulations in everyday life [4]
- Cleaning products
- Paints
- Medicines
- Fertilisers
What is chromatography used to do?
Used to separate the substances in a mixture
What does the ‘mobile phase’ mean in chromatography?
Where the molecules can move (solvent)
What does the ‘stationary phase’ mean in chromatography?
Where the molecules can’t move (paper)
A chemical that travels further up the paper has spent how much time in each phase?
Longer in the mobile phase than stationary phase
How many spots will a pure substance make in chromatography?
1
In chromatogarphy, the time a chemical spends in each phase depends on what 2 things?
- How soluble it is in the solvent
- How attracted to the paper it is
How do you calculate Rf value?
Distance travelled by substance/distance travelled by solvent
Describe the test for chlorine [2]
- Equipment needed is damp litmus paper
- If chlorine is present, paper will be bleached white
Describe the test for oxygen [2]
- Equipment needed is a glowing splint
- If oxygen is present, the splint will re-ignite
Describe the test for hydrogen [2]
- Equipment needed is a burning splint
- If hydrogen is present, you will hear a squeaky pop
Describe the test for carbon dioxide [2]
- Equipment needed is limewater
- If carbon dioxide is present, limewater will turn cloudy
Describe how you would test for carbonate ions [3]
- Put the sample in a test tube and add some dilute acid
- Connect the test tube to a test tube of limewater
- If carbonate ions are present, carbon dioxide will be released that will turn the limewater cloudy
Describe how you would test for sulfate ions [2]
- Add dilute hydrochloric acid and barium chloride to a test tube containing you mystery solution
- If sulfate ions are present, a white precipitate of barium sulfate will form
Why is hydrochloric acid added when testing for sulfate ions?
To get rid of any traces of carbonate ions - these would also produce a white precipitate which would confuse the results
Describe how you would test for halide ions
Add dilute nitric acid and silver nitrate solution to your mystery solution
What colour is silver chloride?
White
What colour is silver bromide?
Cream
What colour is silver iodide?
Yellow
