Chapter 17 Spectroscopy Flashcards
How to find molecular mass from mass spectrum
What is the littke one on the right
When goes in it becomes an ion by losing electron this shown on rightest one
The most right peak that is tall is the molecular ion, and the mass of this is eauak tk moelcukwr mass (minus an ekectron)
Hiwever sometimes extra peak, thid is because a few percent of carbon is an isotrope and carbon 13 instead
What is fragmentation
This js where some moelcukar ions break down into fragemnte , where only thr positive ions are detected (rsdicals not)
You can use this to identify molecules even thou same molecular mas
How do covalent bonds vibrate
Different ways
What affects it
What frequencies can a bond absorb!
They naturally vibrate, stretching big and small, or changing bond angle
- the amount it will bend / stretch depends on strentgh of bond (stringer fsster) snd weight (hesvier slower)
- a bond can only ever absorb the same frequency as its NATURAL FREQUENCY
How do molecules in the atmosphere get infra red to heat up atmosphere?
Infrared radiation by sun re- emitted after absorbed from earth as longer wavlemeght, that water vapour carbin dioxide and methane in atmosphere absorb as it matches their NATURAL FREQUENCY.
Eventually these bonds re emit this energy as radiation that heats up earth and sxcess of these cause escess globsl warming
How does infrared spectroscopy work
1) sample put in IR spectrometer
2) beam of IR of wavenumber 200-4000 is passed
3) molecule absorobs some of these if it matched their natural
4) the computer ANALYSES the emerging beam of radiation and can work put where some have been assorbed, plots this against wavenumber
Some numbers to know about
All molecules produce a CHARACTERISTIC C-H at 2850- 3100, dont confuse with alcohol
IF IT IS BROAD, THEN IT IS A CARBOXYLIC ACID
Application of IR
- pollutants detected by fingerprints, like remote sensors analysijg IR of vehicle emissions ti detect monoxide, dioide and hydrocarbons
- bretahlyser detects characteristic of ethanol, snd how much IR detected = more alcohol drunk
