Organic Analysis
No description yet. This curated deck is ready for daily study.
Card preview (21)
How do you test for an alkene?
Shake with bromine water. Orange-brown to colourless if positive.
How do you test for a halogenoalkane?
1) Add NaOH and warm 2) Acidify with HNO3 3) Add AgNO3 Positive result is a precipitate of AgX Cl = white Br = cream I = yellow
How do you test for an alcohol?
Add acidified potassium dichromate. Orange turns green with primary alcohols, secondary alcohols and aldehydes.
How do you test for an aldehyde?
Warm with Fehling’s solution or Tollens’ Reagent. Blue colour turns red precipitate (Fehling’s) Silver mirror forms (Tollens’)
How do you test for a carboxylic acid?
Add NaHCO3 Carbon dioxide is given off Bubble the gas through limewater Cloudy solution means gas is Carbon Dioxide
What is high resolution mass spectrometry?
Sensitive form of mass spectrometry. Mr of a substance can be calculated to several decimal places.
What is infrared spectroscopy used for?
To help identify compounds by determining the functional groups.
Describe what happens in an infrared spectrometer.
1) A beam of infrared radiation containing a spread of frequencies is passed through a sample. 2) The radiation that emerges is missing the frequencies that correspond to the types of bonds found in the sample. 3) The instrument plots a graph of the intensity of the radiation emerging from the sample called the transmittance, against the frequency of radiation. 4) The frequency is expressed as a wavenumber measured in cm^-1.
What is the fingerprint region?
Before 1500 cm^-1 It is unique and is used to identify the chemical.
What is mass spectrometry?
An analytical technique used to identify compounds and determine their molecular formula.
What is the x axis on a mass spectrum?
M/z value
Why are there multiple peaks when molecules are put into a mass spectrometer?
The molecular ion is shown as a peak but it will also fragment into smaller molecules so those peaks are shown as well.
Why do chemical bonds and atoms absorb infrared radiation?
They are constantly vibrating - they can absorb infrared radiation that is the same frequency as their frequency of vibration.
What effect do heavier atoms have on the frequency of vibration?
Vibrate slower with lower frequency.
What effect does a stronger bond have on the frequency of vibration?
Vibrate faster with a higher frequency.
What do the troughs on an infrared spectrometer show?
The frequencies where radiation has been absorbed by the specific bonds.
Describe the mechanism of the greenhouse effect.
1) UV wavelength radiation passes through the atmosphere to the Earth’s surface and heats up Earth’s surface. 2) The Earth radiates out infrared long wavelength radiation. 3) The C=O Bonds in CO2 absorb infrared radiation so the IR radiation does not escape from the atmosphere. 4) This energy is transferred to other molecules in the atmosphere by collisions so the atmosphere is warmed.
Describe how infrared radiation occurs in the atmosphere.
It causes heat to be trapped within the Earth’s atmosphere. However when chemicals such as CFCs are released into the atmosphere from human activity, the heating effect is enhanced leading to global warming.
How can you use the fingerprint region to identify a molecule?
Compare to a database to look for an exact match to the specimen.
State why mass spectrometry using electrospray ionisation is not a suitable method to distinguish between the isomers.
They all have the same Mr.
Give two ways of maximising the yield of propanal obtained by distillation of the reaction mixture.
Keep the temperature of the reaction mixture below the boiling point of propan-1-ol. Cool the collecting vessel in ice.