Chemistry Forensic Study Cards
FORENSIC CHEMISTRY FORENSIC CHEMISTRY SUMMARY NOTES Ensuring accuracy and contamination of samples for analysis – 1a and 1A |Ensuring accuracy and contamination of samples for analysis – 1a and | | |1A (continued) | |Caution must be taken by scene investigators with regard to their tools, | | |clothing and evidence storage facilities, since debris can lead to false |All scientific analyses must be accurate and reproducible, hence all | |positive results if it has been contaminated by dirty tools or gloves. instruments used to examine samples must be well calibrated and | | |measurements of standards and controls used to ensure accuracy of | |Discuss the following precautions: |sample analysed.
| |Wearing overalls, hair covering, masks, shoe covers to prevent contamination. | | |Samples placed in sterile sealable bags/containers using sterile forceps. Example: Urine analysis in drug testing: | |Laboratories used for forensic examination must be sterile, with absolutely | | |minimal chance of contamination. |Analytical tools/techniques used must demonstrate excellence. | |A lack of sample security and poor laboratory practices can reduce reliable |All instrumentation must be calibrated and monitored consistently to | |evidence to “reasonable doubt” |ensure reliability. | |All standards used must be prepared using accurate techniques and | | |controls used and reproduced to ensure consistency.
| | | | |The forensic chemist must verify chain custody for each sample | | |analysis and document the techniques employed and data collected. | | |They must be prepared to defend their work in legal hearings and | | |trials. |Organic and inorganic compounds – 1b |Different classes and tests for carbon compounds – 1c and 1E | |Organic (carbon) compounds are compounds, which contain mainly carbon and | | |hydrogen, but may also contain smaller quantities of oxygen, nitrogen, sulfur, |Carbon compound class | |phosphorus and other elements. Functional group | |Commonly found or derived from living things: glucose, amino acids, starch and |Distinguishing test | |ethanol. Chemists can also synthesise many organic substances in the | | |laboratories.
alkane | |Inorganic compounds do not contain carbon, except for metallic carbonates, |single bond | |hydrogen carbonates, carbon oxides and carbides. |Add drops of bromine water to sample in the presence of light; very | | |slow reaction. | | | | |alkene | | |double bond | |Add drops of bromine water to sample; rapidly changes bromine from | | |brown to colourless even in the dark. | | | | |alkyne | | |triple bond | | |Add drops of bromine water to sample; slowly changes bromine from | | |brown to colourless even in the dark. | | | | |Different classes and tests for carbon compounds – 1c and 1E. (continued) |Different classes and tests for carbon compounds – 1c and 1E.
| |(continued) | |Carbon compound class | | |Functional group |Acids, bases and neutral salts | |Distinguishing test | | | |Class | |aromatic |Distinguishing test | |benzene ring |Forensic chemistry example | |When drops of bromine water are added to a sample in the presence of light there| | |is no reaction. |Acid | | |pH7 | |alkanoic acid |Cyanoacrylate (superglue) used to reveal fingerprints on glass | |-COOH |surfaces. | |Add drops of aqueous sodium carbonate to sample; bubbles of colourless gas form | | |(CO2). Neutral Salt | | |pH = 6-8 | |ester |Silver nitrate (AgNO3) used to reveal fingerprints on porous | |-COOR |substances. | |Fruity odour; esters containing four or more carbons are water insoluble. | | | | | Inorganic properties of soil and other materials can be useful evidence – 1d |Inorganic properties of soil and other materials can be useful evidence – 1d | | |(continued) | |Soils vary considerably.
The size of soil particles and their chemical |Glass may be useful evidence in a wide variety of cases, for example, | |composition ( clay, silt, sand) can provide very specific location details. |hit-and-run, burglaries and assault. | |Inorganic compounds are important as their composition is rarely altered by |Glass is a hard, brittle, amorphous substance that is composed of silicon oxides | |bacterial action or time. mixed with various metal oxides. Metal oxides include those of Na, Ca, K, Mg, Li,| |Examples of evidence that are composed of inorganic compounds include glass |Ba and B.
| |and soil. Glass may be useful evidence in a wide variety of cases, for |The metal oxides act to modify the properties of the glass. Co, Cr, Mn and Ni are| |example, hit-and-run, burglaries and assault |used to alter the colour of the glass. | |Soils in Eastern Australia often contain relatively high proportions of |The density and refractive index are used to compare glass found at a crime scene| |quartz. |with glass fragments found on a suspect.
| |Both methods require significant statistical treatment to determine the | | |likelihood of the two samples originating from the same source. | |Inorganic properties of soil and other materials can be useful evidence – 1d |Recent example and alteration of an outcome in a forensic investigation – 1e | |(continued) | | | |Case study example | |Paint chips can often provide information to a forensic scientist. | |They can be used to determine if a car was associated with a particular car |The story | |accident or to associate a criminal with a particular crime scene. | | |Automobile paint contains a pigment and binder, which varies depending on the |In early 2000 in the UK a man was arrested based on his DNA matching that from a | |type of paint. |crime scene. Although he lived over 200km from the site of the crime, the police | |Chips from a vehicle can be traced to particular makes and models using |still believed the DNA result was true and concentrated on this man as their | |techniques such as gas chromatography.
|prime suspect. |Evidence samples can be matched to car manufacturers which use the type of |This man has Parkinson’s disease in its advanced stages and he was unable to | |paint found as evidence and eventually lead to narrowing down the possible |perform simple tasks without help, so his lawyer asked for a more detailed DNA | |suspects or the owner of the vehicle. |test to try to prove that his client was innocent of the crime. The police gave | | |the statistics that there was only 1 in 37 million chance that the man’s DNA was | | |a match for another person’s based on the DNA test that was employed. | | | | |Alteration of the outcome | | | | | |The DNA test was a 6-marker test, meaning that six typical base-pair sequences | | |were compared between the two samples.
| | |When the more expensive and time-consuming 10-marker test was performed, it was | | |determined that the man was innocent of the crime. | | | | |The 10-marker test is said to only have a 1 in a billion chance of identifying | | |the person wrongly. | | | | |Recent example and alteration of an outcome in a forensic investigation – 1e |Ethical Issues during analytical investigations – 1B | | |Research these please. | |Breathaliser Example – see photocopy notes. | | | | |Name technology and discuss its advantages over the old technology used to | | |check alcohol levels in drink driving.
| | |Must show a link between the old technology and how the current technology can| | |alter the outcome of an investigation. Use example of a situation. | | | | | | | | | | | | | | | | |Carbohydrates – 2a |First- hand investigation – Modelling monosaccharides and starch. -2B | |Carbohydrates are compounds that contain carbon, hydrogen and oxygen only. |Research textbooks and Internet resources for the structure of the above | |Monosaccharides (these are the basic building blocks of more complex carbohydrates). |carbohydrates.
| |Examples include glucose and fructose.Disaccharides (molecules of these contain two |Construct 3D models of glucose, fructose and starch using molecular modelling | |monosaccharide units linked together). Sucrose (cane sugar or table sugar) is an example. |kits. | | Polysaccharides (molecules of these are polymers made up of long chains of monosaccharide |Glucose units are linked correctly through a condensation polymerisation | |units). Examples include celluloses, starches and glycogen.
|reaction (elimination of water). | | |Class linked glucose units to construct a long coiled structure of starch. |Glucose is a monomer – 2b |Plant and animal carbohydrates -2d | |When two monosaccharides (monomer units) combine a disaccharide is formed. The reaction is | | |called a condensation reaction, resulting in the elimination of a water molecule. Sucrose is |Carb | |a dissacharide, which is formed by linking glucose and fructose together, eliminating water. |Origin | |Polysaccharides are formed when many monosaccharides are linked together in a condensation |Composition | |reaction.
Cellulose (unbranched molecules), starch and glycogen (highly branched molecule) |Found in | |are all polysaccharides formed from glucose monomer units. | | |Soluble starch is called amylose (unbranched-chain molecule); insoluble starch is called |Cellulose | |amylopectin (branched-chain molecule). |Plant | | |Linked (-glucose monomer units.Straight chained water insoluble fibres. | | |Plant cell walls | | | | | |Starch | | |Plant | | |Linked (-glucose monomer units.Coiled structure | | |Stored in cytoplasm of cells | | | | | |Glycogen | | |Animal | | |Linked ( -glucose monomer units.
Highly branched and coiled. | |Stored in muscle and liver cells | | | | |Reducing and non-reducing sugars-2c | glucose | |Reducing sugars (monosaccharides, e. g. glucose and some disaccharides, e. g. lactose and | | |maltose) Reducing sugars have an OH, attached to the C that the O in the ring is attached | | |to.
The chain can flip open to a straight chain structure and expose the –CHO group.It is | | |this aldehyde (alkanal) group -CHO which is oxidized to -COOH group by the addition of extra| | |oxygen. | | |The Cu2+ in the Benedict’s reagent (deep blue Copper sulfate alkaline (NaOH) solution)) are | | |reduced to Cu+1. This is seen from the colour change from light blue to brick orange colour | | |when gently heated. | |Non-reducing sugars do not have the –CHO group and do not reduce the copper ions. | | |Risk Assessment: | | |NaOH is corrosive.
Wear safety glasses to ensure no burns to eyes and when heating ensure | | |that the open end test tube is facing away from any persons to ensure no burns to any parts | | |of the body. | |[pic] | | |Glycogen is similar to the amylopectin (insoluble starch) however it has more side chains | | |(highly branched) | | | |Starch | |Proteins for structure and enzymes –3a |Composition of amino acids and proteins – 3c | |There are two general classes of protein – Fibrous and globular. | | |Fibrous proteins are tough, stringy in appearance and are insoluble in most |Amino acids are compounds that contain both an amine and a carboxylic acid | |solvents. Fibrous proteins form the major structural component of animal |functional group. | |tissue. They are found in skin, hair, muscles, tendons and supporting tissue.
R | |Globular proteins are predominately spherical in shape and are soluble in | | |water. They have specialised functions such as oxygen carriers (in |General formula of amino acids is: H2N-CH-COOH | |haemoglobin) communication agents (in nerve cells) defence agents (in |The COOH group being acidic tends to lose a proton, while the amine group NH2 | |antibodies) biochemical catalysts (in enzymes). |being basic tends to gain a proton.Hence in solution amino acids exist as | | |dipolar ions (zwitter ions) | | | | | |R R | | |H2N-CH-COOH ( +H3N CH-COO- | | |Proteins are long-chain molecules with thousands of amino acid molecules joined| | |together. | | |Protein structure- refer to Powerpoint on moodle (primary, secondary and | | |tertiary protein structure) | |Major functional groups in an amino acid – 3b | Peptide bond-3d | |The major functional groups present in an amino acid are: | | |Amino group (-NH2).At least one amino group is required to give the amino |Proteins are made by the linking of amino acids and the main links are called | |acid some basic (alkaline) properties |peptide bonds.
This linkage involves a condensation reaction between the COOH | |Carboxylic acid group (-COOH). At least one carboxylic group is required to |of one amino acid and the NH2 of another with the elimination of a water | |give the amino acid some acidic properties. |molecule. | | |A covalent C-N bond is produced from the peptide linkage. | |Proteins can be broken (hydrolysed) at different lengths in the chain by choice| | |of enzymes.
This occurs in digestion, both in stomach and in the intestine. | | |Some enzymes are very specific as to which peptide bonds they will break. | | |By using particular enzymes it is possible to break a protein in to several | | |smaller polypeptides. | | | | | | | | | | First hand investigation – Test for proteins-3B | Chromatography and electrophoresis processes compared –3e | | |Similarities | |Chemical |Differences | |Reagent | | |Positive result |Both separate mixtures of amino acids | | |Chromatography separates amino acids on the basis of their solubilities in | |Protein |polar and non-polar solvents. | |BIURET | | |(1ml NaOH solution, then a few drops of CuSO4 solution) |Both powerful tools for forensic chemists in identifying amino acids present in| |Colour change from blue to purple.
|a mixture. NOTE: This is not a process however useful for assessing these | | |techniques in forensic investigations) | | |Electrophoresis separates amino acids based on their charge and size. | |Risk Assessment | | | | | |NaOH is corrosive. Safety glasses are worn to prevent burns to eyes. |Electrophoresis allows the separation of certain amino acids by changing the pH| |(Dropper bottles were used to ensure confinement of chemical and small amounts|of the solution. More effective.
| |of chemical used. | | | | | | |In chromatography, while changing the solvent gives some control over the | | |degree of separation it is less effective. | | | | |Origins of a protein in forensic investigations-3f | First hand Investigation – Modelling proteins-3A | |Electrophoresis is widely ised in the separation of biological |Using molecular modelling kits it is possible to simulate the | |molecules such as proteins and DNA.It can separate individual |formation of a peptide bond and hence the formation pf a | |amino acids within a protein and hence allow the protein itself|polypeptide chain (proteins). | |to be determined. |From this we can determine the composition of proteins and its | |The proteins present on the surface of a red blood cell |generalised structure.
| |determine human blood groups (A, B, AB and O). Electrophoresis |Advantages of modelling: Allows a 3D representation of protein | |of a blood sample identifies the amino acids, and therefore the|structure. Hands on learning and experimenting. Simplifies a | |protein and thus the blood group of the sample. This process |complex process of polypeptide formation. |can be used as collaborative evidence by a forensic chemist to |Disadvantages of modelling – Does not show electrons shared.
| |link or dismiss a suspect to a crime. This method may also be |This is illustrated by plastic bonds. Not to scale. Does not | |used to help identify a victim of a crime or solve paternity |show the involvement of enzymes in protein | |cases. |synthesis/hyrdolysis.
| |First hand investigation –Chromatography -3C |First hand investigation – Chromatography and solvent | |Stationary phase – absorbent paper (filter paper) |polarities. –3D | |Mobile Phase – liquid (solvent). A more accurate determination of pigments in a sample can be | |Substance (plant pigment) to be separated is loaded about about|done by using solvents with different polarities (non | |2cm above the bottom of the paper. This position is called the |polar/polar solvents). | |origin.
|Examples of polar solvents include: water, acetone, ethanol. | |The paper is then placed in a container so that the solvent is |Examples of non-polar solvents include: kerosine, turpentine. | |below the dot (origin). As the solvent rises up the paper, the |If a plant sample contains polar and non-polar pigments then | |components of each sample separate.The rate at which the |the separation of the pigments can be improved by altering the | |components are carried up the paper is dependent on the degree |solvent used.
Eg. Use a polar solvent to separate the polar | |to which the pigment is soluble in a solvent and the degree to |pigments and then repeat the process with the non-polar | |which the pigment adheres to the paper. |solvent to separate the non-polar pigments. | |A pencil line is drawn about 1cm below the top of the paper | | |(solvent front) and process stopped once the solvent reaches | | |the solvent front. | |Paper is dried and components identified by coparison to a | | |control sample.
| | |Refer to Conquering Chemistry text page 478 | | | First-hand investigation – electrophoresis – 3E |Structure and composition of DNA –4a | |Refer to internet simulation. |Deoxyribonucleic acid is found in the nucleus of all living | |Electrophoresis is the separation ofmMolecules to be separated |things. |are applied to a supporting media (agar gel, cellulose acetate |Contains four bases: adenine, guanine, cytosine, thymine. | |or paper. |DNA is composed of two strands colied (double helix) in which | |Most biological molecules are electrically charged, move in an |each strand is composed of linked sugar and phosphate groups | |electric field when current is applied. |(backbone).
| |At low pH they have a net positive charge and will move towards|A base is attached to each sugar in the strand. A-T and C-G are| |the negative electrode. |the complimentary base pairs. | |At high pH, they have a net negative charge and will move |Between an A and T there are 3 hydrogen bonds. Between C and a | |towards the positive electrode. G there are 2 hydrogen bonds which hold the two strands | |The isolectric point is the pH at which there is no electric |together.
| |charge on the molecule. Different molecules differ greatly in |See pictures in Conquering Chemistry: ph 484-486. | |their isoelectric points, so they will migrate at different | | |rates at a particular pH. | | |Anaysis of DNA and identification of individuals – 4b |Draw and label an example of a nucleotide sequence | |DNA is unique to each individual (except for identical twins. | | |It is independent of the organisms’s age and tissue.
Every cell| | |contains DNA. | | |DNA is a robust molecule hence does not degrade rapidly so | | |sample can be preserved. | | |It has high analytical sensitivity and therefore requires only | | |minute samples for analysis. | |Individuals can be identified by analysing the non-coding | | |(introns) sequences along the DNA strand which vary | | |significantly from person to person. (more in point 4c) | | | Processes in DNA analysis for individuals/relationships | Processes in DNA analysis for individuals/relationships | |between people –4c |between people –4c | |Steps in DNA analysis: Steps in DNA analysis: CONTINUED | |1) Separate the DNA from other material in the sample.
Usually |3) This process is repeated for about 25 cycles to amplify the | |done by soaking the sample in a mixture of water-saturated |original DNA strand. | |phenol and water. The DNA dissolves in the water layer from |4)Restriction enzymes are then added which cut the DNA strand | |which it can then be recovered. |in to a series of fragments of various sizes. | |2) Make multiple copies of selected segments of the DNA in |5) Determine the length (number of nucleotides or bases) of | |intron regions using the polymerase chain reaction method |these copied segments by electrophoresis. | |(PCR).
6) Compare samples from different sources or persons to see if | |This is usually done by separating the DNA double strand in to |they match. (Re- visit the electrophoresis internet simulation | |single stands through incubation at 94(C. |activity). | |Short pieces of purified DNA called primers are added which | | |bond to the DNA at lower temperatures. An enzyme is then added | | |(DNA polymerase) which causes the primers to synthesise | | |complimentary strands of each single strand. | |Range of uses of DNA analysis and ethics in DNA data banks – 4A|Range of uses of DNA analysis and ethics in DNA data banks – 4A| |Range of uses in DNA analysis |(continued) | |Identifying the person who produced a biological sample at a |Points For | |crime scene: typical samples are blood, sperm, saliva,skin and |Fingerprints from crime scenes can be compared to stored prints| |hair with blood or saliva prefered.
|in an attempt to identify a culprit. | |Identifying the father of a child in disputed paternity cases |Apowerful tool in identifying criminals. | |Establishing familial links when there is a need to erify the |Innocent people currently are incarcerated for crimes they did | |claim of one person to be a relative of another person. |not commit; if samples had been taken at the time of arrest, | | |these individuals would have been excluded early in the | | |investigative process. | | |Investigators would be able to compare other cases against the | | |arrested person’s DNA profile, just as with fingerprints. | Range of uses of DNA analysis and ethics in DNA data banks – 4A|Range of uses of DNA analysis and ethics in DNA data banks – 4A| |(continued) |(continued) | |Points Against | | |Opposition from civil liberties groups to widespread |The primary concern is privacy.
| |fingerprinting of populations |DNA profiles are different from fingerprints, which are useful | |Breach of individuals privacy |only for identification. |Possibilities of insurance companies demanding routine |DNA can provide insights into many intimate aspects of a person| |screening of such material and getting access to information |and their families including susceptibility to particular | |about genetic disorders could seriously disadvantage affected |diseases, legitimacy of birth, and perhaps predispositions to | |people when seeking insurance. |certain behaviours and sexual orientation. | | |This increases the potential for genetic discrimination by | | |government, insurers, employers, schools, banks, and others. |Destructive testing – 5a |Evidence about samples using analytical techniques – 5A | |If the original sample is modified in some way and/or not |Analytical techniques may be useful in the following ways: | |recoverable, the analysis is called a destructive analysis. |Analysis of organic compounds such as oil spills which enables | |Non destructive testing is required in cases such as: |the scientists to trace the origin of an oil spill in the | |identification of artworks or establishing the authenticity of |ocean.
| |historical artefacts. Therfore forensic scientists are often |Drug testing in biological samples such as urine/blood samples | |not allowed to carry out a destructive test. Ink testing in forged bank notes | |This can be a problem for a forensic scientist for the |Analysis of poisons in autopsy investigations | |following reasons: |Pharmaceutical analysis | |Very small samples are present and repeats of tests are |Cosmetic, explosives, soft drinks, herbicides and drinking | |necessary. |water analysis. | |The requirement of non-destructive testing.
| | |Examples of destructive analysis include instruments such as: | | |mass spectrometry and analytical techniques such as gas/liquid | | |chromatography, atomic absorption spectroscopy and high | | |performance liquid chromatography. | |Gas-liquid and high performance liquid chromatography – 5b |Gas-liquid and high performance liquid chromatography – 5b | |(continued) |(continued) | |Gas chromatography permits the rapid separation of complex |GC is a technique for separating substances based on their | |mixtures in to individual compounds (like organic compounds) , |differential distribution between two phases, one stationary | |and allows qualitative and quantitative determination of each |and the other mobile. | |compound. |In GC a coiled tube is packed with a particles coated in | |This technique is extremely sensitive and can detect minute |silicone oil (high BP) and a tiny sample of the material to be | |quantities of a compound.It is used in conjunction with mass |analysed is injected in to the tube and vapourised. A gas such | |spectroscopy to detect the presence of analgesics, narcotics, |as nitrogen is pumped through the tube and the components are | |anabolic steroids, stimulants, diuretics in urine samples |separated as the gas pushes them through the tube.
| |provided by athletes. |Detection is performed by a flame ioniser. | |A common application of GC in forensic chemistry is measuring | | |the blood alcohol (ethanol) level of drivers. It gives fast and|Refer to flowchart diagrams of Gc in your forensics booklets. | |accurate results.
| |Refer to Forensic Chemistry notes booklet for a detailed | | |assessment. | | |Gas-liquid and high performance liquid chromatography – 5b |Gas-liquid and high performance liquid chromatography – 5b | |HPLC allows sensitive analysis of a wide range of compounds and|(continued) | |is widely used for pharmaceutical analysis. It allows |This method uses a small-diameter steel tube as the column, | |qualitative and quantitative determination of each compound |packed with a finely powdered medium.The solvent is pumped | |HPLC is fast, accurate and can measure the quantity of |through at high pressure which increases the flow rate. | |compounds as little as ppm and ppb.
It can yield highly |It can be carried out at elevated temperatures to enhance the | |reproducible results and it is non-destructive. Hence it is a |separation. | |very sensitive and useful analytical tool. |Detection and measurement of the concentrations is by a UV | | |spectrophotometer and the results are graphed. | |Refer to Forensic Chemistry notes booklet for a detailed |Refer to flowchart diagrams of HPLC in your forensics booklets. | |assessment.
| | | | | | | | | | | | | |Mass Spectrometer – 5c . Refer to interactive internet activity |Mass Spectrometer – 5c (continued) | |sheet on mass spectrometer. |Negatively charged accelerator plates accelerate the positively| |How it Works! |charged ions through the mass spectrometer.The result is a | |Compound to be analysed is uasually dissolved in a common |rapidly travelling ion beam. | |volatile solvent |Ions then pass through a perpendicular magnetic field.
The | |The syringe introduces the sample to the mass spectrometer. |field causes the ions to move in curved paths with a radius | |The vaporisation chamber which is heated to extremely high |dependent on the mass-to-charge ratio of the ions. Only ions | |temperatures vaporises the sample introduced. |with a particular radius reach the collector. By changing the | |The vaporised molecule is then hit with high energy electrons.
electric or magnetic field, different masses can reach the | |The molecule can either lose an electron to become a radical |collector. | |cation, or it can absorb an electron to become a radical anion |The detector identifies the mass of each particle from its | |or there may be no reaction. |path. The data are recorded as a mass spectrum. | | | | |Mass Spectrometer – 5c (continued) |5c – (continued) It is used in conjunction with GC in | |Use for forensic chemists |identifying accidental or deliberate oil spills.Samples from | |A mass spectrometer is widely used to determine relative |oil spills can be analysed and compared to those stored in the | |molecular masses of compounds, identify a range of industrial,|computer library to identify the source of the oil and hence | |environmental and forensic samples by comparison with standard |the ship responsible for the spill.
| |spectra (fingerprinting) and determine structural information |The combination of GC and MS enables forensic toxologists to | |about new compounds. |separate components of a drug mixture, and provides for the | | |specific identification of a drug substance. | |Conditions under which atoms emit light – 6a |Emission of quanta = specific colour – 6b | |Atoms in their normal state do not emit light. [pic] | |When atoms are given extra energy, either by being heated to a | | |high temperature or by being placed in an electric discharge, | | |they can be made to emit light. This is the basis of atomic | | |emission spectroscopy. | | |When atoms are given extra energy their electrons become | | |excited and move to a higher energy level.
When they drop down | | |to their ground state at a lower energy level (nomal state) | | |light is emitted. | |Emission of quanta = specific colour – 6b continued |Certain wavelengths of light are abosrbed – 6c | |White light is the combination of all colours of the spectrum. |Each individual excited atom usually emits only one wavelength. | |The spectrum ranges from 375nm (violet) to 740nm (red). The |Not all atoms in a sample will absorb or be excited in exactly | |spectrum can be split into three basic sections Ultraviolet |the same way and therefore excited electrons will travel to | |light (740nm). |ground state).
| |Each colour corresponds to a wavelength.Red colour has a |Each element produces a different wavelength of light (colour) | |longer wavelength than blue colour. |because each element has a unique energy level system (energy | |The wavelength is inversely proportional to the amount of |shell spacing). Therefore when an atom is excited, electrons | |energy released. This means that as the amount of energy |will travel to different shells according to the element. | |released decreases the wavelength increases.
Less energy is | | |required to produce a red colour (longer wavelength) than blue | | |colour. | | | | |Signature line emission spectrum – 6d |Use of emission spectra in identifying elements in chemicals – | |Since each element has a unique combination of colour |6e | |wavelengths produced by the electrons release of energy, a |Emission spectra can be used in the identification and analysis| |specific series of lines are formed. The series of lines are |of many elements particularly metals. It can be used in the | |called a spectrum. A spectrum formed by the emission of energy |following invesdtigations: | |is called an emission spectrum unique to that element.
|Lead poisoning investigations, | | |Water quality analysis for toxic metals or in water supply | | |control. | |Identification of particular elements in stars, | | |Soil detection to establish the origin of the soil sample. | | |Steel industry to monitor compositions of steels as they were | | |being made. | |First hand investigation – Emission spectrum of Na and Hg – 6A |Origins of a mixture and emission spectra – 6B | |Gas discharge tubes were used and hand held spectroscopes to | | |view the emisison sectra of Na and Hg. Practice exam style questions on identifying elements from | |Electrical energy is used to excite the atoms in the tube, |emission spectra. Refer to exercises in Conquering chemistry | |producing a distinctive colour light for each element.
A hand |text book pages 509-511. | |held spectroscope is used to observe the spectrum for each | | |element. |Emission spectra can be a valuable technique in forensic | |Ensure room is dark to ensure no other light source is present |investigations as it can determine the origin of metal elements| |which would interfere with the element’s spectrum studied. This|found in crime scene samples such as sand samples for example. | |would give invalid results.
Sand composition varies from place to place and if soil | |Gather first-hand information and draw to scale the spectra of |evidence is analysed the forensic scientist can determine the | |individual elements including Na and Hg. |origin of the sample and hence link the evidence to a | |Use second-hand information such as posters/textbook pictures |particular geographical location. | |(reference mateerial) of elemental emission spectra to compare | | |class results. |Refer to point 6e for other examples and expand on them. | |Refer to your prac handout for your results. | | ———————– OH group is now part of the glycosidic bond.
No reaction occurs. Can flip open and be oxidised to an alkanoic acid.