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CHEMISTRY HSC MODULE 8 STUDY NOTES: APPLYING CHEMICAL IDEAS

BY JENNIFER AZZI

INQUIRY QUESTION 1: HOW ARE THE IONS PRESENT IN THE ENVIRONMENT IDENTIFIED AND MEASURED? 1. ENVIRONMENTAL MONITORING ●

Environmental monitoring: describes the processes and activities that need to take place to characterise and monitor the quality of the environment. ● Purpose: ○ Designed to help us understand the natural environment and protect it from any negative outcomes of human activity ○ Part of environmental impact assessments ○ Involve establishing baseline quality ○ Uncovering environmental trends ○ Identifying any variations ○ Determining success of projects ○ Confirming whether environmental goals have been or have not been met ○ Results determine whether projects are placed into action ● Areas of monitoring ○ Air quality: ■ Growing concerns of air pollution – affects environment and animal populations Pollutant Source Carbon monoxide (CO) Motor cars, cigarettes, bush, forest and farm fires, slow combustion stoves Oxides of nitrogen (NO + NO2) Combustion (vehicles and power stations). When heated at high temperatures Hydrocarbons Vehicles and factories using solvents Volatile organic compounds Industry, commerce (e.g. dry cleaners) and homes Particulates (including asbestos) Combustion (transport and industry), many industrial processes (mining), bush fires, farm and forest burn-offs, backyard incinerations; asbestos in dust from insulation and pre-1986 cement board in old buildings and from their demolition Airborne lead Lead smelters, paint dust from renovating old houses. And until recently from leaded petrol Sulfur dioxide (SO2) Combustion, metals extraction (from sulphide ores), some chemical manufacturing Radioactivity Combustion, uranium mining, nuclear weapons testing, nuclear power plants, medical and scientific use of radioisotopes Carcinogenic compounds Benzene and toluene from unleaded petrol, vinyl chloride from plastics manufacture, dioxin from using and incinerating chlorine-containing compounds, cigarette smoke Fluoride Aluminium smelters Chlorofluorocarbons (CFCs) and Before 1996 from refrigeration, air conditioning, foam other halogenated organic plastics, electronics cleaning, halon fire extinguishers compounds Ozone No direct source; formed in photochemical smog ○ Soil quality: ■ Important for farming and agriculture – world’s food production ● Requires monitoring of ions in the soil that are optimal for plant growth ■ Important for the regeneration of jungles and forests

● Essential to keep air clean and free of CO 2 Monitors: ● Erosion ● Soil contamination ● Salt levels ● Level of trace elements ○ Elements that are required by living organisms in very small amounts ○ Concentrations in plants and animals in 1 to 100 ppm range ○ Important for plants: Mn, Cu, B, Mo, Zn Water quality: ■ Four major uses for water: ● For human consumption (drink, food preparation) ● For other human domestic uses (washing, toilet, laundry) ● For agriculture and industry (irrigation, coolant) ● For recreation and aesthetic appeal (swimming, fishing, seascapes – attractive landscapes) ■ Good quality drinking water: ● Completely colourless and clear ● Odourless ● Pleasant taste ● Relatively low salt content ● No pathogens (disease causing agents) ● No poisonous chemicals ■ Good quality environmental water (for wellbeing of the environment): ● Contain adequate concentrations of dissolved oxygen (needed for most aquatic organisms) ● Not contain high levels of oxygen-consuming substances ● Be relatively free of suspended solids (they can interfere with photosynthesis) ● Contain only low concentrations of phosphate and nitrate (higher concentrations promote algal blooms) ○ Algal blooms: excessive growths of algae which cover streams and dams with a green sludge and make water unusable for people, stock or irrigation ■ Criteria for assessing water quality: ● Turbidity (lack of clarity – indicated by amount of suspended solids) ● Total dissolved solids ● pH ● Temperature ● Dissolved oxygen ● Amount of biochemical oxygen demand ● Concentrations of nitrate and phosphate ● Hardness ● Presence of pathogens ● Concentrations of heavy metals such as iron, lead, mercury, chromium, copper, zinc ● Presence of toxic organic compounds such as pesticides and herbicides ■

○

2. INORGANIC QUALITATIVE ANALYSIS ●

A qualitative test/analysis is the process of identifying the ions in a mixture. Through qualitative testing, environmental and industrial samples are monitored to ensure that it does not contain a harmful substance.

Identifying cations in mixtures: When testing for more than one cation, precautions need to be made so that one test does not interfere with the test for another cation. Hence, we separate each precipitate the filtrate from each precipitate and perform the next test on the filtrate. It is vital to ensure that all of the cation is precipitated out before filtrating. A faster method is using a centrifuge: ● A machine that spins test tubes at high speed and so flings the precipitate to the bottom of the tube very quickly The filtrate is then removed with a pipette and then test procedure is carried out like it was only a singular cation. 1. Add HCl: precipitate means Pb2+ is present 2. Filtrate 3. Divide into two portions 4. One portion add F-: precipitate means Ca2+ is present 5. Second portion add H2SO4: if precipitate forms and no Ca2+ is present, then Ba2+ is present 6. Filtrate second solution 7. Add NaOH: no precipitate means no copper or iron whereas if precipitate does form then they are present 8. Add NH3 and centrifuge: a. If green precipitate - Fe2+ is present b. If brown precipitate - Fe3+ is present c. If blue filtrate - Cu2+ is present Identifying anions in mixtures: 1. Add HNO3: if bubbles then CO32- is present 2. To acidic solution add Ba2+: if precipitate forms SO42- is present 3. Filtrate 4. Add ammonia till pH is 8 to 10; if no precipitate forms, add more Ba 2+: if precipitate forms PO43- is present 5. Filtrate 6. Add ammonium salt; if ammonia gas is released (detected by turning litmus paper blue) then OH - is present 7. Acidify with HNO3 then add Ag+: a. If white precipitate forms – Cl- is present b. If cream precipitate forms – Br- is present c. If yellow precipitate forms – I - is present 8. Filtrate 9. Add neutral ferric chloride: if red precipitate forms CH 3COO- is present Precipitates: 2+

OHN Y Y Y

ClN Y Y N

SO42Y Y Y N

CO32Y Y Y Y

PO43- (pH>6) Y Y Y Y

Ba Pb2+ Ag+ Cu2+ Flame Tests: ● Flame tests are highly useful in distinguishing metal ions as each has a different colour due to the varying levels of energy and, in turn, different frequencies and wavelengths of each ion. ● As heat is applied, the electrons gain energy and the valence electrons jump to higher energy levels. When they fall back down to their ground state they release energy as light energy. ● This process is highly useful when distinguishing between solutions that form the same colour precipitate, however, as is visible below, some metal ions produce similar colours which can mislead the

tester, hence causing inaccurate results.

Precipitation: ● Precipitation uses knowledge of precipitation reactions and solubility rules to determine which substances when combined will form a precipitate and which will be soluble. This allows for the identification and monitoring of ions as by adding various substances, whether a precipitate forms and the colour of a precipitate if it does form will allow for the substance in the mixture to be determined. ● Precipitation is particularly useful when identifying and monitoring ions in both environmental and industrial samples.

Complexation Reactions: ● A complex ion is an ion formed when anions or small polar molecules, referred to as ligands, attach themselves to a cation to form a combined ion that has properties that are distinct from their parent ions or molecules, such as a distinct colour change. ● Complex ions are formed due to the metal ions high charge density which results in an ability to strongly attract anions or ligands such as water, ammonia and chloride as is visible below. The process of the ligands forming an ion or compound around a metal ion is referred to as complexation. PRACTICAL INVESTIGATION: IONS IN SOLUTION Aim: To determine one cation and one anion present in an unknown solution using flame tests as well as knowledge of precipitation reactions and solubility rules. Equipment: - Cation - 5 drops of 0.1M Hydrochloric Acid (HCl) - 5 drops of 0.1M Ammonia Solution (NH3) - 5 drops of 0.1M Sulfuric Acid (H2SO4)

-

-

- 5 drops of 0.1M Sodium Fluoride (NaF) - 5 drops of 0.1M Sodium Hydroxide (NaOH) Anion - 5 drops of 0.1M Nitric Acid (HNO 3) - 5 drops of 0.1M Barium Nitrate (Ba(NO3)2 ) - 5 drops of 0.1M Iron (III) Chloride (FeCl3) - 5 drops of 0.1M Silver Nitrate (AgNO3) Safety glasses 8 micro test tubes Test tube rack Permanent Marker Nichrome wire Bunsen burner Heat proof mat Matches Beaker Distilled water One unknown solution containing one cation and one anion

Method: Cation Test 1. Place 5 drops of the unknown solution in each of the 6 test tubes in the test tube rack, each labelled from A to D. 2. Place 5 drops of HCl in test tube A. If a precipitate forms, continue to step 3, however, if no precipitate forms, continue to step 4. 3. Add 5 drops of NH3 to test tube A. If the precipitate remains, Pb2+ is present, however, if it dissolves, Ag+ is present. 4. Add 5 drops of H2SO4 to test tube B. If a precipitate forms continue to step 5, if no precipitate forms continue to step 6. 5. To test tube C, add 5 drops of NaF and if a precipitate forms, Ca 2+ is present, although if there is no precipitate, it is Ba2+. 6. Add NaOH to test tube D. If it turns white, Mg2+ is present, if it turns blue, Cu2+ is present, if it turns green, Fe2+ is present, and if it turns brown, Fe3+ is present in the solution. 7. Repeat the investigation at least 3 times and compare results to ensure reliability.

This method is also visible through the flowchart presented below.

Cation Confirmation Test

Anion Test 1. Place 5 drops of the unknown solution in each of the 2 test tubes in the test tube rack, labelled 1 and 2. 2. Add 5 drops of AgNO3 to test tube 1. If a precipitate forms, continue to step 3, however, if no precipitate forms, continue to step 6. 3. Add 5 drops of dilute HNO3 to the precipitate. If the precipitate dissolves, continue to step 4, however, if the precipitate remains, continue to step 5. 4. If the white precipitate dissolves, it is CO 32-, however, if a yellow precipitate dissolves, it is PO43-. 5. If a white precipitate remains, it is Cl-, if a cream precipitate remains, it is Br -, and if a yellow precipitate remains it is I-. 6. Add 5 drops of Ba(NO3)2 to a second sample. If a white precipitate forms, SO 42- is present, although if no precipitate forms, NO3- is present. 7. Repeat the investigation at least 3 times and compare results to ensure reliability. This method is also visible through the flowchart presented below.

Anion Confirmation Test

Results: Cation Test Results

Tests are as indicated in the flowchart

Test 1

Trial 1

Trial 2

Trial 3

Trial 4

N

No Precipitate

No Precipitate

No Precipitate

─

Test 2

─

─

Test 3

Pr

Precipitate

Precipitate

Precipitate

Test 4

N

No Precipitate

No Precipitate

No Precipitate

Test 5 Cation detected: Photos of the results of this experiment

─

─

─

Barium

Barium

Barium

are visible below.

Cation Confirmation Test Results

Tests are as indicated in the flowchart

Cation detected:

Test 1

Trial 1

Trial 2

Trial 3

Trial 4

Red flame

Green flame

Green flame

Green flame

No precipitate

No precipitate

No precipitate

Test 2

─

Test 3

─

─

─

─

Test 4

─

─

─

─

Calcium

Barium

Barium

Barium

This is also demonstrated through the flowchart below (Figure 7), the red line indicating the process taken during the experiment and the results of each test, although this was not the case in Trial 1 in which an error occurred which will be accounted for in the discussion.

Anion Test Results Trial 1

Trial 2

Trial 3

Trial 4

Tests are as indicated in the flowchart

Test 1

Precipitate ─

Test 2 Test 3

White Precipitate Remains Chloride

Anion detected:

Precipitate ─

No Precipitate White Precipitate

White Precipitate Remains Chloride

Precipitate

─

Sulphate

─ White Precipitate Remains Chloride

Photos of the results of this experiment are visible below.

Anion Confirmation Test Results

Tests are as indicated in the flowchart

Anion detected:

Trial 1

Trial 2

Trial 3

Trial 4

Test 1

No precipitate

No precipitate

No precipitate

No precipitate

Test 2

No precipitate

No precipitate

No precipitate

No precipitate

Test 3

No precipitate

No precipitate

No precipitate

No precipitate

Test 4

No precipitate

No precipitate

No precipitate

No precipitate

Test 5

Cream/White precipitate

Cream/White precipitate

Cream/White precipitate

Cream/White precipitate

Test 6

Precipitate dissolves

Precipitate dissolves

Precipitate dissolves

Precipitate dissolves

Chloride

Chloride

Chloride

Chloride

This confirmation test is also demonstrated through the flowchart below, the red line indicating the process taken during the experiment and the results of each test, although this was not the case for Trial 2 in which an error occurred which will be accounted for in the discussion.

Through this data, it is apparent that the unknown solution was Barium Chloride. 3. INORGANIC QUANTITATIVE ANALYSIS ●

A quantitative test is the process of determining the mass or concentration of ions in a sample.

Gravimetric analysis: ● A gravimetric analysis allows for the mass or concentration of an ion in solution or the amount of an ion in a solid to be determined. It can be used to determine the hardness of water samples or the percentage of an ion in a solid. Example Procedure Aim: - To measure the percentage loss in mass as water is removed from hydrated magnesium sulfate Equipment/materials: - Bunsen burner - Heat mat - Tripod - Pipe-clay triangle - Crucible - Hydrated magnesium sulfate Method: 1. Weigh a clean crucible on an electronic balance 2. Add about 2g of hydrated magnesium sulfate crystals to the crucible and reweigh 3. Place the crucible and contents on a pipeclay triangle supported by a tripod 4. Heat the crucible slowly to allow water vapour to escape slowly for 5-10 minutes 5. Reweigh crucible and contents

Results: Mass of crucible (g) Mass of crucible + hydrated crystals (g) Mass of hydrated crystals (g) Mass of crucible + dehydrated crystals (g)

50 52.003 2.003 51.204

Mass of dehydrated crystals (g)

1.204

Calculations: Difference in mass = 52.003-51.204 = 0.799g % of mass lost = 0.799 x 100 2.003 = 39.89016475 = 39.9% Kickstart method for testing for the presence of sulfate ions Aim: - To conduct a gravimetric analysis to determine the amount of sulfate in a sample solution. Materials: - 1g of Ammonium Sulfate - Barium chloride - 2 x 250mL beaker - 1L volumetric flask - Hot plate - Watch glass - Sidearmed conical flask - Sintered glass funnel (porosity 4) - Desiccator - Measuring cylinder - Deionised water - Magnetic stirrer - Electric balance - Beaker Procedure: 1. Place the 1g of Ammonium Sulfate in a beaker and add 25mL of deionised water to dissolve. 2. Place the beaker on a hot plate and heat up the solution. Then drop in a magnetic stirrer to stir the solution. 3. Take 50mL of the 5% barium chloride solution and heat on a hot plate. 4. Add the hot barium chloride solution very slowly with constant stirring to the hot ammonium sulfate solution. 5. Allow the solution to cool slightly for about 5 minutes. 6. Filter the warm solution into a weighted sintered glass funnel. Wash the precipitate with cold deionised water followed by a small amount of acetone to dry it. 7. Place the weighted funnel into a desiccator and leave overnight to dry. 8. Reweigh the funnel. 9. From the weight of the synthesised barium sulfate, the sulfate present in the fertiliser is able to be determined.

Results: Weight of sintered funnel (g)

95.74

Weight of funnel + paper (g)

96.60

Dried BaSO4 (g)

0.86

Molar Mass BaSO4 (g/mol)

233.43

n(BaSO4) (mol)

= 0.86 233.43 = 0.0037

Underlying Chemistry: - The sulfate ions react with barium ions to form the insoluble solid barium sulphate. Ba2+(aq) + SO42-(aq) → BaSO4 (s) - Barium sulfate has a very small particle size making filtration difficult. - In order to prevent the crystal from forming very fine particles, the precipitation process must be carried out using hot solutions that are being constantly stirred in order to prevent sudden supersaturation of the solution and subsequent immediate precipitation. Precipitation titrations: A Titration is an analytical procedure in which a reagent called a titrant is slowly added to another substance until one of the reactants is exhausted. A precipitation titration involves a reaction which produces a slightly soluble salt that will precipitate out. It is used to determine the concentration of an ion in a solution by using a titrant of known concentration and is similar to an acid-base titration. Two types of precipitation titrations include testing the Chlorine Content in Natural Water using the Mohr Method as well as testing the Hardness in Natural Waters using the Conventional EDTA Complexometric Titration, both of which were undertaken during the Kickstart program. Kickstart - Chlorine Content in Natural Water using Mohr’s Method: What is Mohr’s Method? - It uses silver nitrate solution of a known concentration as the titrant to determine the concentration of chlorides and bromides. - A potassium chromate (K2CrO4) indicator is used. - The method uses the fact that the chromate ion (CrO 42-) is yellow and the insoluble silver chromate (AgCrO4) compound is blood red. - At the end-point, all of the silver from the titrant will be used up by the chloride or bromide. The next drop of titrant will add excess silver to the solution which will react with the chromate indicator. The change in colour of the precipitate indicates the end-point has been reached. Experimental Process: - The precise volumetric determination of chloride requires knowing the exact point at which the precipitate has completely reacted with all of the chlorides that is at the equivalence point. - A solution of potassiu...