C12 Flashcards
What is a pure substance?
A substance made from one type of element or compound
What is a mixture?
A substance made from two+ DIFFERENT elements or compounds that are not chemically combined
What is a formulation?
A mixture that has been specifically designed for a useful product
If a small is pure, will it have a small or large range of boiling/melting point?
Small
Name 2 ways the bp and mp of a substance can be used to tell if its pure or not
- looking at range
- comparing results to a database
What is the test for hydrogen?
Hold a lit splint near sample, hydrogen will burn with a squeaky pop
What is the test for oxygen?
Hold glowing splint near sample, splint will relight if oxygen is present
What is the test for carbon dioxide?
Turns limewater clear to cloudy
What is the test for chlorine?
Turns damp blue litmus paper white
In paper chromatography, what is the mobile phase?
A solvent such as water
If a compound is more strongly attracted to the mobile phase than the stationary phase, it will _____
Travel further up the paper
Why is the baseline drawn in pencil not ink?
Ink will dissolve
How do you calculate Rf?
Substance travelled by substance/substance travelled by solvent
How many spots will a pure substance produce?
1
How can you identify an unknown compound in paper chromatography?
Find the Rf then compare it to known substances in a database
Or
Include known samples and see if any spots travel the same distance
How might you carry out a flame test for metal ions?
- dip a nichrome wire loop into a concentrated hydrochloric acid and then heat it to sterilise
- dip the wire into the unknown sample, then hold it in a roaring flame on a Bunsen burner
- the colour of the flame tells you if certain metal ions are present
What colour flame will sodium produce?
Yellow
Which metal ion produces a green flame?
Copper
What colour flame does potassium produce?
Lilac
Which metal ion produces a crimson flame?
Lithium
What colour flame does calcium produce?
Orange-red
To test for carbonate ions, add ___. If ____ is observed, carbonate ions are present.
Dilute acid, fizzing
___ + acid —-> salt + ____ + _____
Metal carbonate
Water
Carbon dioxide
____ solution can be used to identify some metal ions
sodium hydroxide
which ions form a white precipitate with sodium hydroxide solution?
- Al3+
- Ca2+
- Mg2+
These ions react with sodium hydroxide to produce insoluble metal hydroxides
how can you tell the 3 ions apart?
add more NaOH solution-
aluminium precipitate will dissolve, but Ca and Mg precipitates won’t
You can then use a flame test to distinguish between Ca or Mg- Mg has no flame colour
What colour precipitate does Cu2+ form?
blue
What colour precipitate does Fe2+ form?
green
What colour precipitate does Fe3+ form?
brown
To test for halides, add ___ and then ___ solution. If a precipitate forms, a halide ion is present
- dilute nitric acid
- silver nitrate
chloride ions form which colour precipitate?
white
bromide ions form which colour precipitate?
cream
iodide ions form which colour precipitate?
yellow
What are some positives of using modern equipment?
accurate, sensitive, quick, can work on small samples
but EXPENSIVE
Give an example of and explain an instrumental analysis
Flame emission spectroscopy:
- metal ions emit unique wavelengths of light when they are heated
- a spectrometer analyses the unique pattern of radiation from a heated sample and compares it to other known line spectra
To test for sulfates, add ___ and then ___ solution.
- dilute hydrochloric acid
- barium chloride
In testing for sulfates, if a ___ forms, sulfate ions are present
white precipitate
Why is hydrochloric acid added when testing for sulfates?
To remove any carbonate ions which would form a precipitate with the barium ions
