Chemical Analysis Flashcards
(27 cards)
What is a pure substance?
Contains only one type of element or one type of compound
What do pure substances do in terms of melting and boiling point?
Melt and solidify at ONE point
Boil and condense at ONE point
Describe impure substances?
Mixtures, don’t melt and boil at one temperature, change state over a range if temperature
Describe formulations?
Fuels, cleaning agents,paint, medicine
#Designed to have specific properties
#Complex mixtures where each chemical has a particular purpose
#Components are carefully controlled
What are the 2 phases in chromatography?
*Stationary phase (Doesn’t move) e.g absorbent paper
*Mobile phase (Does move) e.g solvent often paper
What is the equation used when you are doing chromatography with an unknown substance?
Rf= Distance moved by substance ÷
Distance moved by solvent
What happens if you do chromatography with an unknown substance but many substances have the same Rf?
Repeat with a different solvent
When you are doing chromatography what does it mean if you can’t find the unknown substance/Rf on the database?
It’s probably never been analysed before
Why is the chromatography start line drawn in pencil?
If it was in pen, the pen ink would move up the paper with the solvent
Chromatography, what spots does a compound and pure compound produce?
*Pure compound will produce a single spot in all solvents
* Compounds in a mixture may separate into different spots depending on the solvent
Describe chromatography?
^Seperates mixtures into their individual components
^Solvent dissolves the samples and carries them up the paper
^ Each component moves a different distance up the paper (depends on attraction for the paper and solvent)
Describe the test for hydrogen?.
Put a lint split into a test tube with suspected hydrogen gas and it should make a squeaky pop sound
Test for chlorine?
Sodium chlorine and electrolysis bars, turn power pack on, solution starts bubbling, hover litmus blue paper over the bubbling gas and if chlorine is present the paper will start turning white / bleach it
How to test for oxygen?
Put a glowing (no flame) splint inside a glass jar and it will relight if oxygen present
How to test for carbon dioxide?
CO2 is bubbled through limewater (colourless), limewater goes cloudy or milky colour is CO2 is present
Why do we use flame emission spectroscopy?
When we burn solutions containing lots of metal ions it will glow all different colours do this method stops this happening so we can analyse the solutions containing metal ions
Method of flame emissions spectroscopy?
Sample of metal solution placed in a flame and the light emitted passes through a spectroscope which produces a line spectrum
What does the line spectrum used for in flame spectroscopy?
*Identify the metal ions in the solution
*Measure of concentration of the metal ions
Why are the advantages of modern instrumental methods?
*Rapid results
*Very sensitive
*Accurate
*Can be used on small sampled
What are modern instrumental methods and give an example?
They are methods of analysis that rely on machines, better than laboratory tests, example is flame emission spectroscopy
Explain thr flame colour test (required practical)
1) Heat a piece of nichtome wire in a bunsen flame and dip into concentrated hydrochloric acid to clean
2) Dip wire into one of the compounds
(LITHIUM, SODIUM, POTASSIUM)
3) Put in bunsen flame and observe colour change
What colour flame is produced with lithium ?
CRIMSON RED
What colour flame is produced with potassium?
LILAC
What colour is the flame for sodium?
YELLOW
