Module 8 Flashcards
Proton NMR
NMR uses magnetic properties of some atomic nuclei to determine physical and chemical properties of atoms in molecules. Samples are placed in a strong magnetic field, and electromagnetic radiation is applied. Nuclei absorb the electromagnetic radiation and an NMR spectrum is produced which shows this absorption in a spectrum. HNMR is NMR using Hydrogen-1 isotope, its used to determine the type and number of H atoms in a molecule and their environment.
Carbon-13 NMR
NMR uses magnetic properties of some atomic nuclei to determine physical and chemical properties of atoms in molecules. Samples are placed in a strong magnetic field, and electromagnetic radiation is applied. Nuclei absorb the electromagnetic radiation and an NMR spectrum is produced which shows this absorption in a spectrum. CNMR uses the carbon-13 isotope to do this. Each peak on the spectrum shows a C atom in a different environment within the molecule.
Mass spectroscopy
A technique that measures the relative abundance of charged particles with different mass to charge ratios. It works by molecules being split with ionising electrons and made positive before being shot past a magnet. The amount of deflection corresponds to its mass. It provides information about the molecular formula.
Infrared spectroscopy
Infra-red radiation helps to find out about the structure of molecules. It works on the premise that bonds have unique frequencies when they bend, vibrate and stretch. In an infra -red spectrometer, a beam of infra-red light is passed through a sample of the substance being studied. If the frequency of the IR radiation matches the natural frequency of the substance then that energy will be absorbed. To find out which IR frequencies have been absorbed, the radiation which enters the sample is compared to the radiation which leaves the sample. Then the IR spectrum produced is compared to spectra of known substances which are stored in a data bank. Absorbance frequency matches to the specific bond type. frequencies that are less than 2000 wavelength are mostly useless.
Mass spectrometry masses
14 = CH2 15 = CH3 29 = CH3CH2 43 = CH3CH2CH2 17 = OH
Flame Test colours
Ba2+ - Banana - yellow/green Ca2+ - cow-cium - roan cow - brick red Pb2+ - lead pencil - grey/blue Cu2+ - green Cu2+ halide - blue/green Fe2+/Fe3+ - rust - orange/brown Mg2+ - no colour Ag2+ - no colour
Provide an example to analyse the need for monitoring the environment, specifically the atmosphere.
Monitoring combustion reactions is essential as combustion reactions contribute to the buildup of CO2 and carbon by-products in the atmosphere which contribute to the poor health of individuals as well as global warming (from methane, CO2 and vapour due to burning fossil fuels) caused by absorption of the suns radiation which contributes to glaciers melting and rising sea levels.
Provide an example to analyse the need for monitoring the environment, specifically in regards to water.
Ions in the water can come from several sources including; rocks and soils, natural erosion, discharge of wastes from mines, power stations, domestic sewage water, fertilisers, metals. It is essential to monitor the ion concentration in our waterways, water supplies and beaches to check for the presence of pollution and ensure water is safe to use. Eutrophication is another issue that demonstrates the need to monitor water. It is caused by a high conc of nitrate and phosphate ions in waterways due to pollution from fertilisers, detergents sewage etc. This stimulates the rapid growth of algae and cyanobacteria. The Algal bloom means there is a huge proliferation of algae on water surface, blocking sunlight from reaching submerged plants, causing Plant and Aquatic life death. The algae die as they run out of nitrates and phosphates to feed on, and decay using up the O2 dissolved in the water during the decomposition process leaving the water stagnant. The cyanobacteria produce chemicals toxic for aquatic life and unsuitable to drink. Salinity is another issue affecting water sources. In Australia the Murray Darling river basin has been affected by salinity and eutrophication, management practices including more efficient irrigation, lower water table in adjacent flood plains, planting water tolerant trees and shrubs etc have been put into place to counteract this. After the eutrophication process has been completed the only thing that can save the water system is the natural occurence of a huge raine event which can flush out the organic waste.
Provide an Australian example to analyse the need for monitoring the environment.
Residents in Williamtown were exposed to Polyfluoroalkyl Substances (PFAs) from a local fire training area in 2017 which had contaminated their water source. PFAs are dangerous as they are carginogenic contaminants.
Complexation reactions
Ag+ - Diamine silver(I) colourless
Cu2+ - Hexaqua copper(II) blue solution
Fe2+ - Blood-red iron(II) thiocyanate complex
Fe3+ - Hexaaquairon brown solution
Complex ion
A complex ion forms from a metal ion and a ligand because of a Lewis acid–base interaction. The positively charged metal ion acts as a Lewis acid, and the ligand, with one or more lone pairs of electrons, acts as a Lewis base.
what is a complexation reaction
A complexation reaction can be described as a reaction that forms a “complex”. For instance, in adding a cobalt salt, such as CoCl2 (s), to water, we form [Co(H2O)6]2+ (aq). The part of this substance written in brackets is called a complex ion; it involves more than one species but still carries an overall charge (making it an ion) while in solution. Complexes generally form around a transition metal cation.
What process occurs during a flame test?
When a nucleus is irradiated with energy its electrons will momentarily absorb some of that energy. They will then move from ground state to a higher level of excitation momentarily, and fall back down to the ground state, emitting light.
Gravimetric analysis
A quantitative analytical technique that determines the % mass of a chemical species in a sample.
Possible sources of error in gravimetric analysis
Not drying to constant mass – the PPT must be completely dry which is difficult to achieve. Even incubation over several days until mass is constant may not completely dry the PPT and therefore its mass is overstated.
Contamination with other species. Ionic crystals like the BaSO4 PPT readily adhere to other impurities. Thus, the mass is again overstated leading to the same error.
If a student finds that their calculated % mass of PPT is too low, two common sources of error are:
1. Not all of the PPT was successfully filtered out of the solution
2. Some of the PPT is lost during rinsing, transferring and weighing of the sample.
Atomic absorption spectroscopy (AAS)
A type of instrumental analysis that is capable of detecting ppm or even ppb concentrations of metals in solution. It is a simple, rapid method for the determination of metals in solution. In this technique, the solution is aspirated (sprayed) into a flame to produce metal atoms that absorb light from a beam of light passing through the flame.
Describe how you would conduct an investigation to determine the concentration of metal ions in an aqueous solution with the use of atomic absorption spectroscopy.
(Draw sketch)
The element being analysed is determined. – For example, if a soil sample is suspected of containing Hg, then the Hg will be the only element that is tested for.
• A Hg Cathode lamp is selected and inserted into the AAS setup.
• An electrical current causes the gaseous Hg in the lamp to emit its unique spectrum of light and this light is directed at the vaporised sample in the flame.
• The sample in the flame has become atomised and if any Hg is in the sample, some of the light from the lamp will be absorbed by these atoms and these atoms alone.
• The light then passes through a slit and monochromator which selects a single wavelength of light for analysis – this is analysed by the detector and it is displayed as a number
• This number is the absorbance number and it is proportional to concentration.
• If the concentration of Hg in the sample is high, then this means that a lot of the light will be absorbed and not much will get through.
• Absorbance readings are plotted versus their concentration to give a calibration curve.
• Concentration of Hg ions in a sample can be determined using the curve and reading corresponding concentrations for each of the absorbance values obtained.
Check notes for sketch.
