Analysis Techniques Flashcards
where do salts naturally come from?
Come from minerals, heavy metals and organometallic substances
where do salts come from human activity?
Pollution
From mining, agriculture, domestic sources and sewage treatment plants
what are heavy metals?
Heavy metals: metals with density that have a toxic effect on living organisms.
cadmium, lead, copper, chromium and mercury.
Some metalloids (arsenic) have high toxicity so are included.
how are heavy metals released and what happens with them?
Can be released from human activities
Not biodegradable so they just accumulate.
Bioaccumulation: build up of heavy metals in high-order predators.
what are organometallic compounds?
Source of heavy metals
Have at least one carbon-metal bond
Synthetic substances that are used as catalysts or reagents
what is hard water? what is it caused by?
Water needs a lot of soap to lather
Hardness is caused by metals like calcium, magnesium and iron
Ingredient in soap is sodium stearate- when dissolved it acts as a dirt remover
Metal ions in hard water react with stearate to form a precipitate, removing stearate ions and reducing lather
what qualities of water are monitored? (5)
Concentration of ions such as sodium, calcium, potassium, iron (III), chlorine, sulphate and hydrogen carbonate
Turbidity: cloudiness of water due to suspended salts
pH
Hardness
Nutrients like nitrates
how is salinity measured? how does EC change? what measurement does it give? when is it measured?
Tested by measuring electrical conductivity (EC) of a sample
Pure water is a poor conductor (few ions)
As salinity increases, conductivity increases
Gives a measure of total dissolved salts
Conductivity is measured in microsiemens per centimetre mS cm^-1
25 degrees
what is salinity called and how is it measured?
When discussing water quality, salinity is called total dissolved salts (TDS)
TDS (mg L-1) = EC(in mS cm-1) x Kc
Kc is 0.6 in Victoria
what is gravimetric analysis?
Quantitative measure
Determines the mass of salt in a water sample
Forms a precipitate used to analyse silver ions, calcium ions and lead ions
what is stoichiometry? what are mole ratios? why do they change in reactions?
Calculations that concern amounts (number of moles)
Law of Conservation of Mass states that the mass must be conserved (balanced equation).
Mole products may not equal mole reactants
The number of moles is not conserved in a reaction
Coefficients in equations are the mole ratios
what are the steps of stoichiometry?
Balance equation Convert known masses to moles Use the equation to set up mole ratios use the mole ratios to calculate the number of moles of the desired reactant or product Convert moles back to grams if needed
how does gravimetric analysis work? what is an analyte? what are its advantages and disadvantages?
uses precipitation reactions to determine the mass of salts in solutions.
The precipitate allows one ion of the salt to be separated.
Analyte: chemical of interest
Cheap but slow, less accurate, less sensitive and prone to inference by other compounds
what are the steps of gravimetric analysis?
Prepare sample solution (dissolve)
Add precipitation solution in excess to cause complete precipitation
Collect the precipitate by filtration and wash to make sure no soluble components are trapped
Dry- usually heated cooled and weighted until mass is constant
what are the qualities of a good precipitate?
Known formula Low solubility (want most out of solution) Stable when heated (not to decompose into other substances) Be the product of one reaction (other ions should not interfere)
what do calculations involving excess reactants work? what should be used and what do the reagents determine?
One that is used up: limiting reagent
One that is left over: in excess
Identify the excess and limiting reagents and only use the limiting reagent in calculations
Limiting reagent determines the number of products formed
how do substances appear coloured? what is the rule for this?
When a substance absorbs light, it appears coloured.
Colour observed is not the same as colour absorbed.
Colour seen is reflected.
Observed colour and absorbed colours are complimentary.
ROYGBV
GBVROY
what do colorimeters and UV-visible Spectrophotometers determine?
Colorimeter and UV-Visible Spectrophotometer determine concentration by measuring absorbance of radiation in the visible or UV region of the spectrum.
The more concentrated, the more radiation absorbed.
what is colorimetry? how is it preformed?
Measures the intensity of a colour in a sample.
If not coloured, a chemical is added to create colour.
The filter selects a light of an appropriate colour that will be strongly absorbed by the solution.
what are calibration curves? what is a standard solution?
Determine concentration of a substance using standard solutions and their absorbances plotted on a graph.
Standard solution: accurately known concentration.
what is UV Visible Spectroscopy? how is it done?
Uses a monochromator rather than a filter to select light of exact wavelength.
More sophisticated than colorimetry.
A graph is made about which shows where absorbance is maximum (wavelength).
Then use this wavelength to determine absorbance of standard solutions to make a calibration curve.
what are the steps in colorimetry and spectroscopy?
Metal is coloured if needed
A wavelength or filter is used (wavelength most strongly absorbed)
Absorbance for standard solutions is measured
Calibration curve
Absorbance of sample is measured and concentration is determined from calibration curve
Any dilutions are accounted for
what are the uses for colorimetry and UV-Visible Spectrophotometers?
Concentration of urine Blood sugar levels Cholesterol levels Haemoglobin in blood Levels of phosphate in water
how do flame tests work?
Metals emit a colour when heated
Electrons excite to higher levels if given energy
Then it returns, releasing energy as light (unstable)
Energy released corresponds to electron shells so electron shells make a mix of colours
Ionic compounds with the same metal ion have similar colours
Electrons can only go to a shell if they have absorbed enough (no half way)
what are disadvantages of flame tests?
Some metals have no colour
Some metals have similar colours
Cannot determine amount
Sample is destroyed
how is atomic emission spectroscopy preformed? what does it show? what form of analysis is it?
Using a hotter flame and passing light through a prism mean more elements can be tested
Emission spectra are unique for elements (unique energy with electrons)
coloured lines on a black background
Each line is radiation of a specific wavelength and energy equal to the difference in energy between electron levels
Qualitative form of analysis
what is atomic absorption spectroscopy?
Analyses light absorbed
Qualitative and quantitative (presence and concentration of metal ions) black lines on a coloured background
how is atomic absorption spectroscopy done?
Hollow source cathode lamp emits different wavelengths of light that are absorbed
A solution of sample is sprayed into the flame to create atomic vapour
A monochromator is used to select a wavelength for light analysis
A detector measures the amount of light and a computer measures the amount of light absorbed by the sample
what are the advantages if atomic absorption spectroscopy?
Sensitive (ppm/ppb)
Wide range of metals
More accurate that AES
Quantitative and qualitative
what are the uses of atomic absorption spectroscopy?
Magnesium in blood or mercury in fish
Urine and blood analysis for metals
Detection of toxic metals in food
Environmental sampling eg. Pollution in soil
how are calibration curves used in atomic absorption spectroscopy?
Solutions of known metals are produced Absorption is measured Calibration curve is drawn Absorbance of unknown is measured Concentration is measured with curve
what are the organic contaminates in water? how do they go undetected?
dioxins, pesticides, insecticides and oil spills
Toxic
Bind to sediments and go undetected
what are persistent organic pollutants? how do they cause damage? what are some examples?
Toxic to living things
Takes a long time to break down to less harmful products
Bioaccumulate and damage nervous and reproductive systems, cancer, allergies and birth defects
Aldrin (insecticide), chlordane (pesticide, termiticide), DDT (insecticide), Dioxins (industrial chemicals formed as byproducts of combustion) and polychlorinated biphenyls (industrial chemicals used as coolants and lubricants)
how do Persistant Organic Pollutants enter water systems?
Industrial waste Illegal dumping Household and schools Leakage from storage Farming
what are pesticides?
Kill pests
Act like POPs if ingested
what are dioxins? where do they come from? what do they do?
Contain chlorine atoms and carbon-oxygen framework
Byproducts of manufacturing and are produced when toxic waste incinerators are used
High toxicity
Low quantities cause damage
Absorbed in fat and tissue
Babies are vulnerable as they are rapidly developing organs and systems
what are oil spills? what do they do? how are they cleaned up?
Liquid petrolium Kill birds and organisms Contaminate drinking water Fire hazard Economic impact from loss of tourism and impaired fishing Clean up is hard Skimmed off Chemicals absorb oil or break up and disperse it (dispersants) Bacteria break down some
what does chromatography identity?
inorganic and organic substances such as impurities, contaminants etc
what is the stationary and mobile phases?
Stationary phase- paper
Mobile phase- liquid
what do the components do in chromatography? what does sticking depend on?
Components adsorb (stick) onto the stationary phase and then de-adsorb by dissolving into the mobile phase
Sticking depends on polarity of stationary phase and the component molecules
Attraction of components to solvent molecules depends on polarity
what does the rate of chromatography depend on?
How strongly the component absorbs to the paper
How readily the component dissolves in the mobile phase
how are paper and thin layer chromatography assembled? qualitative or quantitative?
Absorbent paper like filter paper
Also could be a thin layer of powder such as aluminium oxide (alumina) on glass or plastic
Qualitative
how are the components of a mixture identified?
calculating Rf
No two components will act the same way in the same conditions, so they will have a characteristic value
Rf values can be compared to known substances
Conditions must be kept the same between knowns and unknowns
Changing the mobile phase will change the rate of adsorption and de-adsorption and change the Rf
Changing film thickness alters Rf
what is retardation factor?
Rf = distance travelled by solute from origin/distance travelled by solvent from origin
what does Rf depend on?
The choice of solvent
Size of sample
Distance travelled by the solvent front
how does column chromatography work?
Stationary phase: a solid or a solid that has been coated with a viscous liquid and packed into a glass column
Sample is put at the top
A solvent (mobile phase) drips through
Tap at the bottom allows eluent (solvent/component) to leave at the rate it enters
Separation happens like paper and TLC but components can be collected and their concentrations compared to standards
Rt (Retention time) is measured as particles move through
how does high performance liquid chromatography?
Solvent carrying sample is forced through solid material under high pressure.
Stationary phase: silica or polymers
Mobile phase: water or ethanol
Sensitive analysis for a large range of mixtures
Separates and identifies mixtures and contaminants in water, drugs in blood, hydrocarbons in oil spills
Components are detected by passing in front of a UV light (less UV light reaches detector as material absorbs it)
Detector is recorded on a chart called a chromatogram
Each component is a peak
Area under the peak is called peak area (larger peak area, high concentration)
what is the acidity of rain water? how does this occur?
Rain water: pH 5.5-6
Carbon dioxide dissolved to form carbonic acid
NO, NO2 and SO2 also cause acidity
why is some water basic?
Water sources are slightly basic from rocks
Rocks have carbonate, bicarbonate, oxide and hydroxide ions
what is the pH of acid rain? how does this happen?
pH as low as 2.4 Greater quantities of SO2, NO and NO2 Power plants Exhausts Wastes
what does acid rain do?
Dear of aquatic life (less than pH 5.5)
Leaching of ions from soil needed for growth
Corrosion of metal fittings
what chemical must standard solution be?
Available in pure form
Have known formula (molar mass can be calculated)
Easy to store without deteriorating or reacting with air
what are the steps of preparing a standard solution?
Step 1:
Weigh solid
Transfer to volumetric flask
Rinse out beaker with deionised water
Step 2:
Add deionised water until half full
Swirl until dissolved
Keep adding water until 1cm below
Step 3:
Final water using a pipette
Add lid and invert
what is molarity?
concentration
what is a burette?
delivers volumes
what is titre?
volume delivered from the burette
what is a pipette?
accurate transfer of volumes
what is aliquot?
known volume delivered from pipette
what is titration?
procedure of mixing reactants until they are present in the exact mole ratio. Determines the concentration of an unknown
what are the steps for titration?
Rinse burette with water and then the solution
Fill the burette and release air bubbles
Read the burette
Rinse the pipette with water and then the substance
Draw up solution and deliver aliquot to the conical flask- last drop is taken into account
Add indicator to conical flask
Titrate until endpoint (permanent colour change for 30 seconds)
Read burette
Get three concordant results (0.1ml of each other)
what is the equivalence point?
neither reactant is in excess
what is the end point?
when colour changes (just past equivalence)
how does a titration curve look for strong acids and bases? what indicator should be used?
Equivalence point is when gradient is steepest (pH 7)
Phenolphthalein changes at 8.3-10
what does a titration curve for strong acids and weak bases look like? what indicator should be used?
Steepest point (equivalence) is pH 4.4 Methyl orange is good- 3.2-4.4 it changes
A sharp endpoint is wanted and some indicators offer that
what are uncertainties?
Issues with calibration of instruments
what is precision and accuracy?
Precise: all results are close
Accurate: results are close to accepted value
what are mistakes?
Avoidable errors
what are systematic error?
Constant bias in measurement that cannot be eliminated by repeating (eg faulty balance)
what are random errors?
Follow no pattern
Reduced by taking multiple measurements
