Hsc Chemistry Practicals 246nv

HSC Practicals In the HSC Chemistry Course we investigate the accuracy, reliability and validity of an experiment in of the first-hand data and the first-hand investigation.

Accuracy refers to the exactness or precision of a measurement; relating to its proximity to the accepted true value. The accuracy of the investigation can be improved through equipment upgrades such as using data loggers and sensors, and the calibration of equipment against known samples to test how accurate the device is and to adjust it accordingly. The accuracy of the data is dependent upon the accuracy of the equipment, human error is not a valid reason for inaccurate results. Inaccurate data can be the result of systematic errors (equipment defects) or due to the level of uncertainty of the equipment i.e. a 500 mL beaker measures with a level of uncertainty of ±10 mL while a volumetric pipette can measure with a level of uncertainty of ± 0.01 mL. Reliability refers to the degree with which repeated observation and/or measurements taken under identical circumstances will yield the same results. For all experiments, reliability can be improved through repetition, removal of outliers, averaging, and comparing with other students. A set of results is reliable if all the measurement taken of the same thing obtain approximately the same value. Validity refers to whether the processes and resultant data you are measuring is caused by the phenomena you are interested in. In a valid experiment only one variable must be changed and others must be kept constant. You assess validity by investigating the dependent, independent and controlled variables in the experimental design. Also, you want to also talk about what assumptions are being made and what limitations exist in the experiment, and possibly the need for a control experiment. An experiment test's a natural chemical phenomena, therefore to increase the validity you can test it on a greater range of chemicals, proving that it is universally true and not specific to the named chemicals used; for example in the bromine water test we can test more alkene-alkane combinations. The experimental data's validity is an overarching concept that cannot be attained without the data being both accurate and reliable. Experimental data obtained via interpolation is more valid than extrapolation, as when you extrapolate, you are assuming that the trend observed between your data points will continue beyond them.

identify data, plan and perform a first-hand investigation to compare the reactivities of appropriate alkenes with the corresponding alkanes in bromine water

1. 2. 3. 4. 5.

Place 5 mL of cyclohexane and cyclohexene in separate, labelled 10 mL test tubes. Add 2 mL of bromine water to each test tube using a dropper. Stopper and gently agitate each test tube to the same extent. Allow the test tubes to rest for 30 seconds. Observe and record any colour changes.

Control: Repeat the above steps for a 10 mL test tube containing 5 mL of distilled water. solve problems, plan and perform a first-hand investigation to carry out the fermentation of glucose and monitor mass changes

1. 2. 3. 4. 5.

Add 2 g of weighed dried yeast to a 100 mL conical flask. Add 20 mL of glucose solution using a measuring cylinder. Weigh and record the mass of the apparatus using an electronic scale. Place the apparatus in an electronic water bath, held at 30 – 35 C. Over successive days, re-weigh the flask and record the mass changes until a constant mass is reached.

I have not included the possible usage of a Buchner flask with a stopper and delivery tube, and a beaker containing limewater. This is not necessary for the exam, but it is useful to understand that it is used to indicate the production of CO2, through the formation of a cloudy white precipitate, and thus indicating that fermentation is occurring. Control: Repeat the above steps without the addition of yeast. identify data sources, choose resources and perform a first-hand investigation to determine and compare heats of combustion of at least three liquid alkanols per gram and per mole

1. Record the initial mass of the spirit burner using an electronic scale. 2. Add 200 mL of water to the aluminum can using a measuring cylinder. 3. Set up apparatus as drawn below:

4. Record the initial temperature of the water using a thermometer. 5. Light the burner and heat the water until the temperature has risen by 20 C. 6. Allow the apparatus to cool, before reweighing and recording the spirit burner's final mass. 7. Repeat the above steps for each alkanol.

perform a first-hand investigation and gather first-hand information to measure the difference in potential of different combinations of metals in an electrolyte solution

1. 2. 3. 4. 5. 6. 7. 8.

Clean metal strips with steel wool. Place 50 mL of each metal ion solution into separate, labelled 100 mL beakers. Add the metal strips to the beaker containing their respective metal ion solution. Soak strips of filter paper in KNO3 solution. Connect the two half cells together using the filter paper as a salt bridge, Connect the metal strips in each half cell to a voltmeter using connecting wires. Record the voltage produced. Repeat with other combinations of half cells. Use a new salt bridge each time to avoid contamination.

I have been non-specific here, but the exam may intend for you to use the metals stated in a question or to use named metals from the experiment you performed in school. perform a first-hand investigation to prepare and test a natural indicator

1. Boil 100 g of shredded red cabbage in 250 mL of water until the water turns darkpurple. 2. Allow mixture to cool and decant dark-purple indicator solution into a clean beaker. 3. Add one drop of each 1M test solution in separate spots on a spotting plate using a droplet. Some possible test solutions include HCL, CH3COOH, NaCl, NH3 and NaOH 4. Add one drop of the indicator to each spot and record colour changes using a droplet. identify data, plan and perform a first-hand investigation to decarbonate soft drink and gather data to measure the mass changes involved and calculate the volume of gas released at 25̊C and 100kPa

1. 2. 3. 4.

Record the mass of an unopened soft drink can using an electronic scale. Open the can, allowing the CO2 gas to escape. Place the can on a hotplate, on low heat for 10 minutes. Allow the can to cool before reweighing and recording the mass change.

Control: Repeat the above steps for a washed soft drink can containing only distilled water.

perform a first-hand investigation to use pH meters/probes and indicators to distinguish between acidic, basic and neutral chemicals

pH probes 1. Calibrate the pH probe before use by placing the probe in buffer solutions, of known pH, and adjusting the meter to give appropriate readings. 2. Rinse the probe with distilled water between measurements and blot dry using a piece of tissue, to avoid contamination. Indicators 1. Add one drop of the test chemicals to separate spots on a spotting plate using a dropper. 2. Add one drop of the indicator solution to each spot using a dropper. 3. Compare the colours observed with a pH indicator chart. perform a first-hand investigation using the preparation of standard solutions

1. Calculate mass of anhydrous sodium carbonate required to prepare 250mL of 0.5M solution. 2. Weigh the dry solid in a 100mL beaker. 3. Dissolve the sample in a small volume of distilled water using a stirring rod. 4. Rinse a 250 mL volumetric flask, funnel and pasteur pipette thoroughly with distilled water. 5. Transfer the solution from the beaker into the volumetric flask using the funnel. 6. Rinse the beaker and funnel into the flask for complete transfer using a wash bottle, 7. Fill the volumetric flask with distilled water up until a few centimeters below the 250mL mark. 8. Add distilled water carefully until the bottom of the meniscus is at the graduated marking, using the pasteur pipette. 9. Stopper the flask and invert several times to homogeneously mix the solution. analyse information from secondary sources such as computer simulations, molecular model kits or multimedia resources to model a chemical reaction. •

They allow us to visualise which various bonds are being broken and which formed and they give us an idea of the shape of the molecule being made and their atomic constituents. They illustrate the stepwise nature of the process. They allows us to appreciate the three-dimensional nature of the process.

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The relative sizes of, and distances between the atoms are unrealistic. The dynamic nature of molecules and their bonds is not shown. They are an oversimplification of complex chemical process.

I have answered this question very generally using a Molymod kit. When asked for a specific reaction it is good to specifically say what the balls, connectors and motion of separating or ing them represented e.g. hydrogen atoms, double bond opening up, addition reaction and etc.

identify data, plan, select equipment and perform a first- hand investigation to prepare an ester using reflux

1. Add 10 mL of 1-pentanol, 15 mL acetic acid and 1 mL of concentrated sulfuric acid into a 100 mL round-bottom flask, using a measuring cylinder. 2. Add ceramic boiling chips to the flask 3. Assemble the reflex apparatus as drawn below.

4. Connect the tubing to the tap and condenser, and turn the tap on so there is uniform flow. 5. Heat the mixture under reflux for 45 minutes, and allow 5 minutes to cool. Turn off tap after. 6. Remove the flask and decant content into a separating funnel containing 15 mL of water. 7. Stopper the funnel and shake 8. Allow layers to separate and then drain off and discard the lower aqueous layer. 9. Add 15 mL of Na2CO3 to remove sulfuric acid. 10.Again shake, allow to separate, drain and discard the lower aqueous layer. 11.Place 5 g of anhydrous magnesium sulphate into a conical flask. 12.Pour the remaining contents of the funnel into the conical flask. 13.Decant the final ester into a round bottom flask, after 10 minutes.

You will never have to recite the entire experiment, rather the HSC tends to ask for specific parts such as setting up the reflex apparatus or the filtration/purification process.

identify data, plan, select equipment and perform first- hand investigations to measure the sulfate content of lawn fertiliser and explain the chemistry involved

1. Grind up a sample of fertilizer into a fine powder using a mortar and pestle. 2. Weigh out 1 g of the powder using an electronic balance. 3. Dissolve the powder in 100 mL of distilled water in a 250 mL beaker using a stirring rod. 4. Filter the solution in a clean 250 mL beaker using filter paper. 5. Add 25 mL of 1M HCl to remove carbonates. 6. Heat the mixture just below boiling using a hotplate. 7. Slowly add 20 mL or an excess amount of 20% BaCl2 solution with constant stirring. 8. Digest and stir the mixture for 30 minutes. 9. Allow the beaker to cool and then rest in ice. 10.Filter the solution through a sintered glass funnel. 11.Wash the precipitate using a wash bottle, once with distilled water and again with acetone. 12.Dry the precipitate on the sintered glass funnel in an oven. 13.Cool it in a desiccator. 14.Weigh and record the funnel and precipitate. 15.Repeat Step 12 – 14 until a constant mass is reached.

You do not need to memorise this process as they would never ask you to recite one, rather it is important to understand the purpose of each step.

I have gone more in-depth into the industrial practicals as the HSC tends to test them more holistically when they ask about them. identify data, plan and perform a first-hand investigation to model an equilibrium reaction 1. 2. 3. 4. 5. 6. 7.

Label two 50 mL measuring cylinders 'A' and 'B'. Fill A with 50 mL of water. Invert a 5 mL graduated pipette into 'A' and allow the water to rise. Place a finger on the tip and carefully transfer the trapped water into 'B'. Repeat steps 3-4 to transfer water from 'B' to 'A'. Perform 30 cycles of steps 3-5 and record the volumes of 'A' and 'B' each time. On the 15th cycle, transfer the water from 'A' to 'B' using a larger 10 mL pipette before continuing with the 5mL pipette.

Advantages: • Shows the effect of changes in concentrations on reactants and products. • Simple, visual and easy to understand. • Emphasises that equilibrium occurs in a closed system. Disadvantages: • Cannot show effect of temperature and pressure changes on equilibrium. • Cannot show the effect of a catalyst.

choose equipment and perform a first-hand investigation to gather information and qualitatively analyse an equilibrium reaction 1. 2. 3. 4.

Fill two 75 mL ampoules with NO2(g). Place one ampoule in a 150 mL beaker of warm water (50C) with a water bath. Place the other ampoule in a 150 mL beaker of cold water containing crushed ice. Observe and record colour changes.

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Apply L to talk about this endothermic reactions

Safety Concerns: • • •

May cause or intensify fire; oxidiser. Contains gas under pressure and heat: may explode. Causes severe burns and eye damage.

Safety Precautions: • • •

Do not breathe in vapors if leak occurs. Wear protective gloves, clothing and safety glasses. Conduct experiment in a fume cupboard.

perform first-hand investigations to observe the reactions of sulfuric acid acting as: – an oxidising agent – a dehydrating agent Dehydration 1. 2. 3. 4.

Add 50 g of sucrose into a 150 mL beaker. Place the beaker in a fume cupboard. Pour 25 mL of Sulfuric acid (concentrated) into the beaker and step away. Record any observations:

A black foam-like product will form. Oxidation 1. Place a clean strip of zinc in a 150 mL beaker. 2. Pour 20 mL of Sulfuric acid (concentrated) into the beaker. 3. Record any observations:

Zn(s) will degrade, the solution is colourless but H2(g) can be indicated with the pop test.

identify data, plan and perform a first-hand investigation to identify the products of the electrolysis of sodium chloride 1. Add 100 mL of water and 10 g of NaCl in a 150 mL beaker (dilute NaCl solution) 2. Add 100 mL of water and 60 g of NaCl in a 150 mL beaker (conc. NaCl solution) 3. Clamp a U-tube to a retort stand. Attach two carbon electrodes to a 6 V power source and place one in each opening of the U-tube. Pour some dilute NaCl in. 4. Add 2 drop of Universal indicator at both openings. 5. Turn on the power source and record any colour changes at the anode and cathode. 6. Repeat steps 3-5 but with concentrated NaCl solution.

Dilute NaCl: •

Anode reaction: (2) ◦ red colour ◦ optional: oxygen gas reignited glowing splint

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Cathode Reaction: (4) ◦ purple colour ◦ optional: hydrogen gas confirmed using pop test

Concentrated NaCl: •

Anode reaction: (1) ◦ green colour ◦ optional: distinct Cl2(g) smell when carefully wafted

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Cathode Reaction: (4) ◦ purple colour ◦ optional: hydrogen gas confirmed using pop test

perform a first-hand investigation to carry out saponification and test the product 1. 2. 3. 4. 5. 6. 7. 8. 9.

Dissolve 5 g of NaOH pellets in 30 mL of water in a 150 mL beaker. Add 5 mL of coconut oil and 5 mL of methylated spirits to emulsify. Boil the mixture on a hot plate and continuously stir it Allow it to cool when the layer of oil has disappeared. Add 10 mL of NaCl solution and bring back to boil, stirring continuously. Allow the solution to cool; you will observe lumps of soap forming. Decant the solution to keep the soap. Flush the salt 2-3 times with NaCl solution. Allow the soap to dry on a piece of filter paper.

Testing: 1. Use six 50 mL test tubes and place 5 g of salt in two of them, 5 mL of synthetic detergent in another two and nothing in the last two. 2. Fill each test tube with 20 mL of water and 5 mL of oil. 3. Stopper each test-tube and shake vigorously for the same amount of time. 4. Record whether an emulsion or separate layer was formed and height of foam. • • •

Detergent and Lab soap will both form an emulsification. Detergent will produce more foam than Lab soap. Water + Oil test tube will form two separate layers.

perform a first-hand investigation to demonstrate the effect of soap as an emulsifier •

same as testing in above experimental

perform a first-hand investigation to gather information and describe the properties of a named emulsion and relate these properties to its uses 1. Mayonnaise was made by slowly adding vegetable oil to the egg in a jar, shaking vigorously throughout. Repeat with 5 mL of vinegar and continue shaking until creamy. 2. Investigate its properties Properties: • • •

Emulsification of vegetable oil and egg yolk. Lecithin in egg yolk is a strong emulsifier An even texture and appearance.

Use: •

A common food dressing

perform a first-hand investigation to assess risk factors and then carry out a chemical step involved in the Solvay process, identifying any difficulties associated with the laboratory modeling of the step To model the decomposition of sodium hydrogen carbonate: 1. Carefully place 2 g of NaHCO3 into a pre-weighed test tube and fit with a gas delivery tube and stopper. 2. Clamp the test tube in a slanted fashion onto a retort stand and place a bunsen burner under the tube. 3. Fill a beaker with 200 mL of limewater, and place the gas delivery tube into it. 4. Heat the test tube for 5 minutes, recording all observations. 5. Reweigh the test tube and determine the loss in weight.

Results: • • •

The formation of water vapour at the mouth of the test tube. The lime water bubbled and turned a cloudy milk phase, indicating presence of CO2. The test tube decreased in mass, indicating loss of water vapour and CO2.

Safety Concern: • • •

Na2CO3 is a slightly toxic if ingested and also a skin irritant. Inhalation of Na2CO3 aerosols can cause lung oedema. Lime water is corrosive, leading to chemical burns.

Safety Precautions: • •

Care must be taken when handling the substances. Hands must be washed immediately after coming in .

Difficulties associated: •

The difficulty encountered in this experiment was that it was not clear when the reaction had gone to completion, as both NaHCO3 and Na2CO3 is a white powder. ◦ Observation of when CO2 stops bubbling through limewater allows us to identify when the reaction is complete.

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The model over-simplifies a large scale industrial step in the process.