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What is Infrared Spectroscopy
analyses the interaction of molecules with IR light. It primarily gives information about the
bonds or functional groups present in a molecule
It also graphs transmittance against wavenumber.
Infrared radiation absorbed by a molecule causes…
Bonds to vibrate at different energy levels
How to calculate wavenumber
To calculate wavenumber, the inverse of wavelength should be taken! It’s the number of wavelengths that fit into 1cm.
Define transmittance
measures how much radiation is transmitted or passes through the sample.
When radiation is absorbed, this value decreases
Compared to bonds that contain atoms with low molecular masses, bonds with atoms of higher masses will absorb radiation of…
Lower frequency.
Bonds between atoms of higher molecular mass absorb lower frequency IR radiation compared to bonds between atoms of lower molecular mass.
True or false… On an infrared spectrum, transmittance values are always lower than or equal to 100%.
TRUE!
A transmittance value of 100% means all the infrared radiation passes through the sample and none is absorbed. When radiation is absorbed, transmittance values drop.
A peak in an infrared spectrum indicates that radiation has been…
Absorbed
Why are flame tests good for qualitative investigations?
- Metal ions emit colour that aligns with a specific/characteristic wavelength - Falls within visible spectrium
- Heating metal ions gives them energy - allowing them to move to higher energy orbital aka excited state.
- Ions release this energy they absorbed and move back to ground state.
- Energy released - has wavelength and characteristic flame colour
What is the importance of testing and monitoring the environment using examples
Examples 1. Bangladesh water – ammonia in the water –> using electrical currents to test water if safe to consume or not.
Example 2. Shade balls in seattle? lake - water used for consumption as well. In the sun chlorine reacts with bromine making bromide - highly toxic for consumption.
In a flame test- what colour does Lithium ion produce
Crimson Red
In a flame test- what colour does bArium ion produce?
Apple Green - light green colour
In a flame test- what colour does sOdium ion produce
Orange /Yellow
In a flame test- what colour does Potassium Ion produce?
Lilac - (light purple)
In a flame test- what colour does Calcium ion produce?
Brick - Red
In a flame test- what colour does Stronium ion produce?
not in syllabus
Bright red
In a flame test- what colour does Copper (II) Ion produce?
Blue (bluish/green)
How to test for Lead (II) ions in solution?
5 drops 0.1M potassium iodide = bright yellow precipitate
What are the tests/and steps for an anion test?
Go to ontenote flowchart to check
- carbonate ions - Nitric acid.
- No bubbling = test for hydroxide, phospahte, chloride, bromide/idodide ions - add silver nitrate solution
- no precipitate = test for sulfate ions - add barium nitrate
- no white precipitate = test for acetate - at Fecl and heat
- No red brown colour = Anion may be nitrate ion
Gravimetric analysis: what is it and example
To determine the amount of analyte through measuring mass.
Example: Sulfur content of fertiliser.
* Amount of barium in found in solution and due to 1:1 Stoich ratio - the amount of sulfur can be found
Method:
1. Grind sample of fertiliser with morar and pestle
2. Weigh sample of fetiliser and record mass
3. Dissolve fertiliser in deionsied water - may need to be warm mixture
4. Filter mixture (dicard residue)
5. Add 20ml of 1M HCL to filtrate and stir.
6. Add excess 1M BaCl2 to solution to filtrate.
7. Filter mixture with sintered glass filter Keep BaSO4 residue.
8. Dry BaSO4 precipitate collected
9. Carefully wiegh dried precipitate
10. Determine mass of SO4 and hence mass of S and %
What is a precipitation titration
Precipitation titrations are a form of titration useful in the determination of anions –
especially halides (chlorides, bromides and iodides).
These titrations involve the use of a precipitating agent such as silver nitrate
Requirements of precipitation indicators:
* The colour change should occur rapidly.
* The colour change should take place with change in the titration curve (that is, at
the equivalence point!
Example chromate ion - from Mohrs method
What is Mohr method
Mohr’s method:
Potassium chromate solution (CrO 42- ions) is used as the indicator.
Used in the determination of halide (Clî or Brî) concentration
- Silver nitrate (AgNO 3) is the titrant (in the burette).
- Solution containing the unknown concentration of halide ions is the analyte (in the conical flask)
- A small amount of K2 CrO 4 is added to the conical flask to act as the indicator.
- The end point is detected by the formation of red-brown Ag 2 CrO 4 , silver chromate which appears once all the X - ions are consumed and excess Ag+ reacts with the CrO4- ion.
This method is known as a direct method.
Ag + + Cl- –> AgCl(s)
Once Cl- is used up:
2Ag + + CrO4 2- –> Ag 2 CrO 4(s)
