Module 8 - Applying Chemical Ideas Flashcards
Purpose of AAS
Atomic Absorption Spectroscopy is used to determine the concentration of metal ions in a substance at very low concentrations
Set up of AAS
A hollow cathode lamp with the metal to be analysed emits electrons at a certain wave length, a flame containing the vaporised sample absorbs some of the light, the monochromator selecting the wave length and the detector records the intensity
Using an AAS curve
Requires a calibration curve, using the absorbance to find the concentration
Units of concentration in AAS
ppm or mg/L
Purpose of mass spectrometry
Used to determine molar mass of element and the isotopes
Set up of mass spectrometry
Sample is vaporised and ionised, molecular ion breaks apart into smaller fragments, ions are accelerated through an electric field and deflected by the magnetic field with the amount depending on their mass-to-charge ratio (m/z), then detected
What is the base peak in mass spectrometry?
The highest peak is the most abundant peak (the highest)
What is the parent peak in mass spectrometry?
The peak with the highest m/z (furtherest to the right), usually the molar mass
Purpose of infrared spectroscopy
To determine the bonds/functional groups
How IR spectroscopy works
IR radiation causes molecules to stretch, bend and vibrate, each bond vibrating at a characteristic frequency
Set up of IR spectroscopy
IR is split into two beams so it is shot at sample and reference, the splitter and detector recording the results
The region below 1500cm in IR Spectroscopy
The fingerprint print - Can be compared with spectra of known compounds, but not as useful for functional groups
Purpose of NMR
To map the atomic structure - the presence and position of molecules
Set up of NMR
Matter is placed in a magnetic field, nuclei must have an odd number of nucleons, moving from low to high energy state allowing them to absorb energy (radiofrequency radiation)
Standardising chemical in NMR
TMS (very shielded)
Name of peaks in NMR and their number of peaks
Singlet - no split
Doublet - Two peaks
Triplet - Three peaks
Quartet - our peaks
Number of peaks in H1 NMR
How many different chemical environments
Location of the peaks in H1 NMR
The closer to the right is more shielded, left is less shielded
Splitting in H1 NMR
n+1 peaks shows how n*H1 nuclei on neighbouring carbons
Area under the curve in H1 NMR
Corresponds to the relative number of hydrogens present in the environment
Differences in C13 vs H1 NMR
Height and splitting is not important
Reading 13C NMR graphs
Use data sheet to determine functional groups
What is colourimetry?
To determine the concentration of a coloured analyte in solution by absorption of a specific wavelength of visible light
The Beer-Lambert Law
Concentration is proportional to the amount of light absorbed. A = e[molar absorptivity, depends on substance]l[path length]c[concentration] or A = log(Io[incident light]/I[transmitted light])
Set up of colourimetry
Light source -> coloured filter -> sample solution -> detector -> recorder
Colours absorbed in colourimetry
Solutions absorbs the complementary colour of the visible colour (e.g. a blue solution absorbs red) which must be chosen
How to use colourimetry
Create a calibration curve using a series of standard solutions
What is UV-Visible spectrophotometry?
Use of the absorption of UV, visible electromagnetic radiation (EMR) to deduce molecular structure. The substance must absorb UV and EMR to be useful. It is qualitative
Set up of spectrophotometry
Light source -> monochromator -> sample solution -> detector -> recorder
How to use spectrophotometry graph
Monochromator allows for the selection of specific wavelengths. Maximum absorbance (highest point on graph) + minimal interference with other substances
How spectrophotometry operates
Measures absorbance at a range of wavelengths to plot absorbance vs wavelength, creating a spectrum
Availability of reagents in chemical synthesis + design (example)
Haber process - take Nitrogen from the air and Hydrogen from natural gas (CH4)
Reaction conditions in chemical synthesis + design (example)
Haber process - 500oC (exothermic but compromise which increases rate); 200atm (moderate as high risk + cost); magnetite (iron) catalyst; set up to remove ammonia so it favours the forward reaction
Yield and purity in chemical synthesis + design (example)
Haber Process - Yield is maximised by using a moderate temperature (500oC which slows down yield but increases rate) & moderate pressure (200atm to increase yield but balance cost + risk); condenser used to liquefy NH3 while pumping back in N2 + H2 purifying the product; must also monitor the incoming gas so it’s pure as O2 at high temps can explode
Industrial uses of chemical synthesis + design (example)
Ammonia from the Haber process used in fertilisers (ammonium nitrate), explosives, household cleaners/detergents, refrigerant gas
Environmental, social and economic issues of chemical synthesis + design (example)
Solvay process for Na2CO3 (used in glass making)
Environmental - Mining CaCO3 can disrupt ecosystems; waste product of CaCl2 is discharged into the ocean (as already a lot of ions, but not in rivers)
Social - Site must not be too close to people due to noise and dust pollution, but close enough for workers
Economic - Site must be close to supply of raw materials and market to sell; accessible by transport
What a precipitation titration involves + how to find equivalence point
Involves using Ag+ to detect halide ions (Group VII); Equivalence point determined by formation of a second coloured ppt, formation of a coloured complex ion, conductivity measurements
