Download pdf - EXPERIMENT FEST - newcastle.edu.au · The possible career paths listed below include a range of opportunities for graduates at degree, honours, ... Manufactured products, including

HANDBOOKChemistry

EXPERIMENT FEST

Experiment FestPage 2

CONTENTS

Introduction

Welcome

Studying Chemistry

Metal Analysis by Atomic Absorption Spectroscopy:

Concentration of Sodium in Sports Drinks

Determination of Sulfate in Lawn Food

Analysis of Nitrate Ion Concentration in Water

3

4

6

8

13

18


INTRODUCTION

Experiment Fest is an experiment program designed to provide enriching educational experiences for senior high school students who are studying Physics, Chemistry and Biology. Experiment Fest is supported by the University of Newcastle’s Faculty of Science and takes place at both the Callaghan and Ourimbah (Central Coast) campuses ofthe University of Newcastle.

All experiments are complemented by notes, follow-up discussions and questions to enhance your learning experience.

For booking information contact the Experiment Fest Team on [email protected]


WELCOME

Welcome to the Faculty of Science at the University of Newcastle.

Experiment Fest is a wonderful chance to give you practical experience which complements your classroom learning while giving you a first hand look at University life and facilities. Science is an exciting field of study, allowing you to move with the times and contribute actively and responsibly to society. There are many education opportunities in science after high school. Here in the Faculty we provide study and research programs in fastmoving modern fields that make our world work.

The Faculty staff and students who will be taking you through the experiments today are involved in contemporary science research. Please ask questions and utilise your time with them.

Take this day to enjoy being out of the class room, exploring science with fellow students and participating in valuable experiments and discussions which will help you in your HSC and beyond.

I wish you well in your studies. I hope you apply yourselves to the learning process with enthusiasm and you enjoy your time at the University. We hope to see you studying with us in the future!

Best wishes,

Prof. Lee Smith Pro Vice-Chancellor – Faculty of ScienceUniversity of Newcastle

CHEMISTRY


STUDYING CHEMISTRY

Why study chemistry?Chemistry is truly the “central science”. It is the science of the molecular scale, and it is at the molecular level wheremajor advances are being made in many diverse areas such as medicine, drugs, nanotechnology, new materials, andthe environment. A sound knowledge of chemistry is required to fully understand many other areas of science, andthis is why the study of chemistry is either compulsory or recommended by many other disciplines in the University.Chemistry opens the door for many careers because training in chemistry is essential for many positions in industry, ishighly desirable for science teaching, and is useful for careers in the public service and management. Both the publicand the private sectors increasingly draw their higher management echelons from chemistry graduates.But, most importantly, it is just so fascinating! If you want to understand the workings of the world around you - thenchemistry is for you!

Opportunities for further studies in Chemistry:The Bachelor of Science degree program at the University of Newcastle provides a foundation of knowledge, skillsand attributes that allows graduates to be employable not just today but into the future and to contribute actively andresponsibly to society. Majoring in Chemistry, you have the opportunity to sample and/or specialise in any one of thefollowing:

• Analytical Chemistry• Chemical Biology• Chemistry• Chemometrics (double major)• Environmental Chemistry• Forensic Chemistry• Geological Chemistry• Industrial Chemistry• Materials Chemistry• Medicinal Chemistry• Surface and Colloid Chemistry

Research in Chemistry at the University of NewcastleThere are various groups here at the University which are committed to research in chemistry. Groups include:

• Analytical and Environmental Chemistry• Battery Materials and Applied Electrochemistry• Coordination and Bioinorganic Chemistry• Marine Natural Products and Chemical Ecology• Medicinal Chemistry and Chemical Biology• Polyoxymetalates and Catalysis• Surface and Colloid Group


• Analytical Chemist• Clinical Research Coordinator• Developmental Chemist• Environmental Chemist• Energy Technologist• Forensic Chemist• Geochemist• Industrial/Production Chemist• Laboratory Manager• Laboratory/Research Assistant• Meteorologist• Organic/Synthetic Chemist• Pharmaceutical/Medicinal Chemist• Reproductive Medicine / IVF Chemist• Research Scientist• Science Information/Education Officer• Science/Chemistry Teacher• Sciences Technician• Scientific Patent Attorney / Technical Advisor• Scientific Policy Officer• Scientific Writer

Careers in Chemistry:

The Faculty of Science and IT care about our students and are interested in giving as much direction as possible to those making career choices and beyond. The possible career paths listed below include a range of opportunities for graduates at degree, honours, and post graduate study levels.

For more information please visit the University’s website:www.newcastle.edu.au

For more information on the Faculty of Science check out our website: www.newcastle.edu.au/faculty-of-science


METAL ANALYSIS BY ATOMIC ABSORPTION SPECTROSCOPY: CONCENTRATION OF SODIUM IN SPORTS DRINKS

SAFETY GLASSES AND A LABORATORY COAT MUST BE WORN AT ALL TIMES DURING THE LABORATORY SESSION

RISK ASSESSMENT

Extract from HSC Chemistry Syllabus:Manufactured products, including food, drugs, and household chemicals, are analysed to determine or ensure their chemical composition.

Gather, process and present information to interpret secondary data from AAS measurements and evaluate the effectiveness of this in pollution control.

Atomic Absorption Spectroscopy (AAS) allows the detection of very small concentrations from samples of air, water or food. This activity depends on your ability to manipulate data and dilution factors. The absorbance values obtained using solutions of known concentration enable you to draw a calibration graph. Use the specific absorbance data provided to read off the corresponding concentration for the sample.

Hazard Substance, Apparatus, Proce-dure

Precaution/ Action

Burette Filling: Use a plastic funnel to fill burette; remove equipment from retort stand and fill over sink

Pipette Filling: Do not pipette by mouth. Use a pipette bulb to fill pipette.

http://www.differencebetween.net/object/difference-between-gato-rade-and-powerade/


IntroductionAAS is a commonly used technique for determining the concentration of metal ions. The analysis of metals is important in a range of applications from trace analysis of metals – including pollutants - in water and soil to quality control of materials such as iron and special steels.

Quality control in products is an important commercial tool. In this instance, the presence of salts such as sodium in sports drinks is critical for their usefulness in replacing the salt loss by athletes through perspiration. Too little salt and the product will not be effective. However, the addition of too much salt may diminish the taste of the product, as well as slow the rate of absorption of the liquid in the stomach.

A flame is needed to atomise a sample in order to measure it. The temperature of the flame is selected based on what metal(s) are being analysed. As shown in Table 1, the less reactive metals require more energy (heat) to be atomised. The most common method for atomizing a sample is using an acetylene (C2H2) / air mixture.

The detection limit between metals varies considerably. Under acetylene/air conditions, the detection limit for iron is 5 µg/L (or 5 parts per billion, also expressed as 5 ppb), sodium – 0.3 ppb; zinc – 1.5 ppb and mercury – 150 ppb.

The basis of this analytical method is that for a given metal ion, the absorption is directly proportional to the concentration (A a [ ]), that is, the more atomised metal present, the higher the absorbance. We use this principle to prepare a calibration curve and use this to determine the concentration of the species in the unknown.

As with any analytical method, the determination of metals by AAS can be affected by the presence of other species. Remember a sports drink is not just sodium ions and water! It is important that we are aware of everything else in the solution and take steps to counter their effect. Any species that changes the observed signal, while the concentration of the metal remains unchanged, is termed an interference.

http://www.pelletlab.com/images/2303.jpg

Table 1: Flame gas temperatures and applications.

Gas Combination Max. Temp. (K) Elements atomizedNatural gas/air 1800 Group 1A (Li, Na, K)Acetylene/air 2250 Transition metals (Fe, Cu, Zn) Acetylene/N2O 3000 Group 2A (Ca, Mg, Ba) Group 3A (Al)


Types of Interference

In this experiment we are primarily interested in determining the sodium content of sports drinks by AAS. However, potassium is also present within sports drinks, and may affect the analysis of sodium (resulting in an interference).

In AAS, it is very important that the standards we prepare are as close as possible to the sample under investigation. When using a calibration curve to calculate an unknown concentration, your results will only ever be as good as your standards. Bad standards give bad results! In this investigation, the interference due to other ions (potassium) is accounted for in by adding potassium as well as sodium to the standard solutions.

The reason for adding potassium is simple. Alkali metals such as sodium have low ionisation potentials (lose electrons easily) and readily ionise in the flame. This results in sodium ions being present as well as sodium atoms, however, only sodium atoms absorb the unique radiation that is generated (via the lamp in the AAS) and measured by the instrument. When this occurs, it is called ionization interference.

The simplest way to overcome this effect is to add another alkali metal that will ionise more easily than the sodium, such as potassium. This is termed an ionisation suppressor. By having a high concentration of electrons in the flame, ionisation of the sodium is suppressed, keeping 100% of the sodium as atoms which can be measured.

To show the effect from the presence of potassium, the sports drinks will be analysed using two sets of standard solutions. One series will be made containing only sodium ions, while another series will be prepared with the same concentrations of sodium ions and will also contain a large excess of potassium ions.

PrincipleYour analysis will determine the concentration of sodium present in a range of sports drinks. A series of standard solutions of sodium will be prepared. Our selection of the range of these standards is based on our understanding of the concentration of the unknown as well as the knowledge that high concentrations of substances cause deviations from the linear relationship between absorption and concentration.

Preparation of the sample for analysis involves dilution of the initial sports drink sample. This is required to adjust the concentration of sodium into the correct range for the operation of the instrument and to ensure that the absorption reading is within the range of the standards.

Supplied solutions:1,000 mg/L Sodium (NaCl) Stock10,000 mg/L Potassium (KCl) Stock


ProcedurePreparation of Standards

1. Prepare a series of four standard sodium solutions containing 0, 10.0, 20.0, 50.0 mg/L (ppm) of sodium. To do this,measure accurately, 0, 1, 2 & 5mL of the sodium stock solution (from the supplied burette) respectively into four separate100mL volumetric flasks and make each flask up to the mark with distilled water. Label them as “Na stds-1, 2,” etc.2. Prepare a series of sodium standards containing a constant amount of potassium ions (as KCl).3. Prepare the same series (i.e. 0.0, 10.0, 20.0 and 50.0 mg/L) as in Step 1 above by measuring out the same volumeof sodium stock solution into four new volumetric flasks. At this point, add 20mL of the 10,000 mg/L potassium (KCl) stocksolution (measured with a measuring cylinder) to each volumetric flask and make up to the mark with distilled water. Labelthis series as “Na-K stds-1, 2,”etc.

Preparation of Sports Drink Sample.

4. Pipette a 5 mL aliquot (precisely known volume – use a pipette) of Gatorade into the provided 100 mL volumetricflask. Add 20mL of the 10,000 mg/L potassium stock solution (measured with a measuring cylinder), then add distilledwater to the 100.0 mL mark. (What dilution factor have you just introduced?).5. Stopper all flasks and thoroughly mix the solutions by inverting the flasks at least 6 times.6. Analyse these solutions by AAS for sodium as described below.

Analysis7. Measure the absorbance of the “Na stds” series (all 4 solutions). Solutions are measured from lowest to highestconcentration. Record these results in the Table below. From the data, prepare a plot of Absorption Vs Concentration Na stds.8. Measure the absorbance of the “Na-K stds” series (all 4 solutions). Solutions are measured from lowest to highestconcentration. Record these results in the Table below. From the data, prepare a plot of Absorption Vs Concentration Na-Kstds.9. Measure the absorbance of the diluted sports drink. Record the absorption value in the Table below.10. From the absorption reading, determine the concentration of Na from each calibration graph.

You must take the dilution factor into account when reporting the actual concentration of sodium in the sports drink.


Table 2: Absorbance Values of Na standards. Concentration of Na stds

(mg/L)AAS Absorbance

Na-stds Na-K stds

0.0

10.0

20.0

50.0

Table 3: Absorbance of Sports Drink. Name of sports drink

Sodium concentration from bottle*

AAS Absorbance

Dilution Factor

Concentration of sodium in sports drink determined from ‘Na stds’ graph.

Concentration of sodium in sports drink determined from ‘Na-K stds’ graph.

*Express all values in mg/L

Results

Follow-up activity:1. Which of the two values you have reported in Table 3 above would be expected to be closer to the “real” value?Justify your choice.

2. Draw a block diagram of an AAS unit and use this to briefly explain how the system operates. https://www.youtube.com/watch?v=_KZjb9G3hB8

3. What else could be analysed using AAS?


DETERMINATION OF SULFATE IN LAWN FOOD

Extract from HSC Chemistry Syllabus:

Identify data, plan, select equipment and perform firsthand investigations to measure the sulfate content of lawn fertilizer and explain the chemistry involved

Analyse information to evaluate the reliability of the results of the above investigation and to propose solutions to problems encountered in the procedure.

Hazard Substance, Apparatus, Procedure Precaution/ Action

Burette Filling Use a plastic funnel to fill burette; remove equipment from retort stand and fill over sink.

Ammonia solution Toxic by inhalation. Causes burns. Risk of seri-ous damage to eyes. Use in fume cupboard.

Pipette filling Do not pipette by mouth. Use a pipette bulb to fill pipette.

BaCI2 Harmful by inhalation. Toxic if swallowed. Skin contact may produce health damage.Avoid skin contact. Wash affected area well with water.

Enriochrome Black T indicator Cancer suspect agent. Cumulative effects may result following exposure. Avoid skin contact. Wash affected area well.

http://altura.speedera.net/ccimg.cata-logcity.com/210000/211600/211630/Products/5673991.jpg


RISK ASSESSMENT


Introduction

The traditional method used to determine sulfate concentration is using gravimetric analysis. This is easily achieved by weighing the dried pre-cipitate formed (barium sulfate) when barium ions are added to a sulfate solution. Although this is a simple procedure, it is very time consuming.

The solution has to be boiled for nearly 1 hour to ensure that the barium sulfate precipitate forms particles large enough to be successfully filtered. Once filtered, the precipitate then needs to be oven dried to remove residual water.

The concentration of barium ions in solution can be easily measured by completing a complexometric titration with ethylenediaminetetraacetic acid (EDTA) using a metallochromic indicator.

The indicator Eriochrome black T (EBT) forms a red coloured complex when bound to metal ions (e.g. Ba), and a blue complex when metal ions are absent.

EDTA is a strong chelate - a species that reacts with metal ions to form a stable metal complex. It reacts in a 1:1 ratio with barium ions by ‘stealing’ them away from the weaker eriochrome black complex. When enough EDTA is added in the titration, all barium ions are no longer complexed with the eriochrome black indicator which results in the solution turning blue, signaling the end of the titration. This is illustrated in the reaction scheme below:

Ba[EBT] + [EDTA] + Ba[EDTA] + [EBT]Red Blue

We have chosen ammonium sulfate [(NH4)2 SO4] as the lawn food to analyse.

An alternative method, the one we will use, involves performing a back titration. A back titration is only used when the endpoint of the forward reaction cannot be observed directly. This can occur when the reaction being measured is very slow, produces side reactions, or when the analyte is an insoluble solid.

In this experiment, we cannot directly measure when the barium sulfate precipitate stops forming (due to the sulfate fertiliser being completely consumed) because you cannot see through the already formed cloudy precipitate. Instead we use a col-ourometric indicator to measure the amount of excess barium that remains after the reaction is complete.

Barium ions react with sulfate ions in a 1:1 ratio as shown in the ionic equation representing the reaction below. If we know how much barium is present before the reaction, and how much barium remains after the reaction, any difference between these values must be how much has reacted with the sulfate. Because of the 1:1 ratio of the reaction, this difference will also equal the amount of sulfate present.

http://en.wikipedia.org/wiki/Eriochrome_Black_T


TitrationsThis analysis requires each group to perform 2 titrations. The first of these is a ‘blank’ titration. It determines the amount EDTA required to react with all the Ba2+ ions before the reaction with sulfate. The second titration is the ‘test’ titration. It measures the amount of Ba2+ ions that remain in solution after the reaction with sulfate.

When completing the titrations, carry out the titrations in duplicate and record your values to 2 decimal places (that is, estimate between the graduations on the burette). Ideally, the two results should be within 0.2 mL to be acceptable. Record your results in the Table below.

InterferencesThis method will not give a meaningful result in the presence of phosphate, as the solid barium phosphate will also form, leading to an incorrect estimation of the amount of barium ions which reacted with the sulfate.

The presence of other metal ions (such as copper, zinc, etc) will lead an inaccurate estimation of sulfate. These ions will also react with EDTA and if present, will lead to more EDTA being added than what is needed to react with the barium ions in solution. The sample analysed today does not contain these interferences.

Supplied solutions:Freshly prepared fertiliser solution[(NH4)2SO4] of known concentration (6.6 g/L) Freshly prepared ~0.2 M barium chloride BaCl2 solutionFreshly prepared 0.1 M EDTA solution (Note: record the exact concentration – 4 decimal points).Concentrated ammonia buffer solution NH3/NH4Cl (CAUTION: see safety note above).Freshly prepared Eriochrome Black T indicator solution.

To assist the completion of the experiment, samples of the lawn fertilizer pretreated with barium ion and predigested will be available. You will prepare fresh samples for the group following you.


Procedure

1. Pipette 1 x 50.0mL of the supplied ammonium sulfate solution into two separate beakers.

2. Pipette 25.0mL of 0.2M barium chloride into each beaker, then cover the solution with a watchglass and place onthe hotplate in the fume cupboard. These solutions will be used by the group undertaking the experiment after you. Taketwo of the predigested samples from the hotplate for your experiment.

3. Return the fertilizer solutions to your bench, place them in an ice bath to cool. While this is taking place, carry outa blank titration on the 0.2M barium chloride solution as follows:

• Pipette 25.00mL of 0.2M barium chloride into a 250 mL conical flask• Add 10mL of concentrated ammonia/ammonium chloride buffer• Add 6 drops of Eriochrome black T indicator• Titrate with 0.1M EDTA from red/purple to a blue endpoint.• Record the volume of EDTA required in the Results Table below as Vb.

4. Repeat step 3 to obtain a duplicate result for the blank titration. Record the volume in the table and average thetwo blank titration results.

5. Remove the now cooled fertilizer solutions from the ice bath and filter the BaSO4 precipitate from the first sampleusing the Millipore filtration apparatus on you bench. Make sure that you place a 0.45µm filter paper in the apparatus beforecommencing to filter.

6. Transfer the clear filtrate to a 250mL conical flask. This will be used to carry out the test titration as follows:• Transfer all of the filtrate into a 250 mL conical flask• Add 10mL of concentrated ammonia/ammonium chloride buffer• Add 6 drops of Eriochrome black T indicator• Titrate with 0.1M EDTA from red/purple to a blue endpoint.• Record the volume of EDTA required in the Results Table below as Vt.

7. Repeat steps 6 for the second fertilizer sample.

8. Use the information in the Results Table to calculate the percentage of sulfate ion in lawn fertilizer.

Steps 1 and 2 should be carried out in duplicate (2 samples). Get steps 1 and 2 underway before commencing the titration.

This apparatus is very expensive. Take great care!Make sure that you use the filter paper and not the separating paper!Check with demonstrator if you are unsure.


Follow-up activities:1. Can you suggest any changes in the experimental procedure that may improve the accuracy?

2. What was the reason for adding the ammonia/ammonium chloride buffer?

3. When is it useful to use the back titration method of volumetric analysis?

Concentration of fertiliser (g/L) 6.6 g/L

Exact concentration of EDTA (4 d.p)M

Volume of EDTA required for blank (Vb)

Titration 1 (2 d.p)mL


Average Titre: (2 d.p)mL

Volume of EDTA required for test solution (Vt)



Average Titre: (2 d.p)mL

Difference in volume of EDTA (corresponding to Ba2+ used, thus SO42- present) -Vb - Vt mL

moles of EDTA consumedmoles

moles of sulfatemoles

Initial mass of fertiliser in 50.0 mL sampleg

Mass of sulfate determined experimentallyg

Results:


IntroductionNitrate and phosphorous are together known as nutrients when found in water bodies. These two species, if present in sufficient quantities, allow excessive plant growth and eventual stagnation of the water. This process is known as eutrophication.

Nitrogen is tied up in biological systems. Nitrate and nitrite ions are important indicators of pollution by organic materials as nitrogen from decomposing organic substances often ends up as nitrate or nitrite ions. The determination of nitrate is often difficult because of the low levels found, and the distinct possibility of interfering materials (organic matter) being present.

SpectrophotometryWhen determining nitrate it is important to choose an analytical method that suits both the interferences that are present and the level of analyte in the solution. Spectrophotometry is an excellent analytical method. In visible spectrophotometry (400-700nm), light impinges on a coloured substance causing certain wavelengths of light to absorbed. The remaining wavelengths of light in the visible spectrum are reflected and transmitted to the eye of the viewer. For example, a purple dye absorbs wavelengths in the green-yellow parts of the visible spectrum and reflects red and blue wavelengths of light.

ANALYSIS OF NITRATE ION CONCENTRATION IN WATER

Extract from HSC Chemistry Syllabus:

• Perform first-hand investigations to use qualitative andquantitative tests to analyse and compare the quality of water samples.

• Gather, process and present information on the range andchemistry of the tests used to: monitor possible eutrophication ofwaterways.

WEAR GLOVESContact with combustible material may cause fire. Toxic by inhalation. Cause severe burns. Risk of serious damage to eyes. Reacts violently with water. Use only in fumehood with auto-dispenser.

http://altura.speedera.net/ccimg.catalogcity.com/210000/211600/211630/Products/5673991.jpg

Hazard Substance, Apparatus, Procedure Precaution/ Action

Burette Filling Use a plastic funnel to fill burette; remove equipment from retort stand and fill over sink.

Concentrated hydrochloric acid


RISK ASSESSMENT


Spectroscopy can also be carried out using other parts of the electromagnetic spectrum such as the ultra-violet (400-10nm) and infrared regions (700-1050nm). The principle of evaluation remains the same however, provided you have a device for detecting the intensity of the radiation in the chosen region of the spectrum. In this experiment you will utilize UV radiation to quantify the amount of nitrate ion in an unknown sample.

The Beer-Lambert Law. The intensity of a coloured solution depends upon the concentration of the coloured component and the path length through which the light travels. The Beer-Lambert Law quantitatively relates the extent of absorption of light to the concentration of absorbing species in solution. Importantly, this law refers to a single wavelength and not to the absorption band as a whole.

The Beer-Lambert Law states that, at a given wavelength, the relationship between the intensity of the incident and transmitted monochromatic light in terms of the concentration of the absorbing species in solution and the pathlength is given by:

I tI o

= 10 - ecd

where:I0 is the intensity of the incident light of definite wavelength,It is the intensity of the transmitted light of the same wavelength,ε is the molar absorptivity (in units of L mol-1 cm-1) at that wavelength. It is a constant for a pure substance,c is the concentration of the absorbing substance (in mol dm-3, i.e. mol L-1), d is the pathlength (in cm) of the absorbing substance.


Using mathematics (a log transformation) this equation may be simplified to a linear form:

A = ecd

Measurement of the absorbance of light by solutions is accomplished using a spectrophotometer. In a spectrophotometer a light source emits a range of wavelengths which are passed into a mono-chromator. The monochromator in turn selects a single wavelength of light which is passed through the sample to be measured.

The incident light beam is absorbed to some extent by the sample and the intensity of the transmitted light (of the same wavelength as the incident light) is measured by a photoelectric device.

I oI t

log10A = absorbance

The electrical circuit is so designed that the output of the instrument is calibrated to read directly in absorbance or percentage transmission.

In this experiment you will use a spectrophotometer to determine the concentration of nitrate in an unknown water sample. This will be carried out in the UV region (400-10nm) of the electromagnetic spectrum. Good results may be obtained if the water contains little or no organic matter (which also absorb in the UV). The method will involve taking an absorbance spectrum of nitrate ion in the range 190-400 nm to select the strongest absorbance wavelength for your measurements. You will then construct a calibration plot, otherwise known as a Standard Curve (see below) from the absorbances of the nitrate samples of known concentration. The concentration of the unknown NO3

- sample will then be

determined by measuring it’s absorbance and reading the concentration from the Standard Curve.

This experiment relies on the same analytical concept that was utilized in the AAS experiment. The basis of this analytical method is that for a given analyte (nitrate) ion, the absorption is directly proportional to the concentration (A α [ ]), that is, the more nitrate ions present, the higher the absorbance of radiation. In this experiment nitrate ions absorb wavelengths of UV light.

polarisersource

sample

detector

spectrum

signalprocessing

diffraction grating

where


Procedure

1. Prepare nitrate calibration standards for 0, 5, 10 and 15 mg/L by adding 0, 5, 10 and 15 mL, respectively, of the100 mg/L stock nitrate solution, adding 1 mL HCl to each flask, and then making them up to the mark in a 100 mL volumetricflask with ultra-pure water.

2. Prepare you sample in a similar fashion by diluting 20 mL of the natural water sample in a 100 mL volumetric flaskwith HCl (1 mL) and ultra-pure water.

3. Using your 0 mg/L standard record a background absorbance spectrum in the range 190-400 nm.

4. Measure the absorbance spectrum of the remaining standards and sample over the same wavelength range.

5. Prepare a calibration graph by plotting the absorbance maximum in each spectrum and hence determine theconcentration of nitrate ion in the natural water sample.


Results

Follow-up activities:1. How would nitrates & phosphates get into the water supply? i.e where do they come from?

2. What happens when too much nitrate & phosphate are both present in a water system?

3. How would the levels of nitrate & phosphates be monitored by a governing body such as Hunter Water?

Solution Wavelength Maximum(nm)

Absorbance at Maximum

0 mg/ L standard

5 mg/ L standard

10mg/ L standard

15mg/ L standard

Unknown

Unknown Concentration=