1 List of Experiment TodayPreparation of Nitrogen Monoxide and Study of Its Chemical Properties (microscale experiment) Making of Silver Nanoparticles Quantitative Analysis of a Mixture of Carbonates(Inquiry-Based Approach)
2 Website of Workshop ResourcesResources on June 2017(Today) Link: rce/CHEM02/internal/ Resources on February 2017 Link: HEM01/internal/
3 Redox Reactions, Chemical Cells and ElectrolysisPreparation of Nitrogen Monoxide and Study of Its Chemical Properties (microscale experiment) Curriculum Link Topic VII Redox Reactions, Chemical Cells and Electrolysis
4 Background Nitrogen monoxide (NO) is a colourless gas. It can be prepared by the reaction of sodium nitrite with acidified iron(II) sulphate solution: Nitrogen monoxide is very reactive and is readily oxidised in air to produce nitrogen dioxide:
5 Background Nitrogen monoxide has a very limited solubility in water.The oxidation state of nitrogen in nitrogen monoxide (NO) is +2. Since typical oxidation state of nitrogen ranges from -3 to +5, nitrogen monoxide has both oxidising and reducing properties with suitable reagents.
6 Tasks To prepare nitrogen monoxide from sodium nitrite and acidified iron(II) sulphate solution. To study the oxidising and reducing properties of nitrogen monoxide with (1) acidified potassium permanganate solution, (2) bromine water, (3) acidified iron(II) sulphate solution, and (4) air (oxygen).
7 Chemicals NaNO2(s) FeSO4/H+(aq) 1 M NaOH(aq) KMnO4/H+(aq) Br2(aq)Deionised water
8 Part A: Preparation of Nitrogen Monoxide1. Add 250 cm3 of deionised water into a 250 cm3 beaker. 2. Pour about 100 cm3 of 1 M NaOH solution into another 250 cm3 beaker. 1 M NaOH solution deionised water
9 Part A: Preparation of Nitrogen Monoxide3. Carry out the following for a 100 cm3 glass syringe: (a) Insert the plunger into the syringe, and push and pull the plunger several times. Check whether the plunger moves smoothly in the syringe.
10 Part A: Preparation of Nitrogen Monoxide3. (b) Cap the syringe with the syringe cap or your finger and check whether the plunger moves smoothly in the syringe. If it does, there may be a leakage and then you should ask for help.
11 Part A: Preparation of Nitrogen Monoxide4. (a) Weigh about 0.25 g of NaNO2(s) with an electronic balance and transfer it into a vial cap. Make sure that the NaNO2 solid is evenly placed in the cap.
12 Part A: Preparation of Nitrogen Monoxide4. (b) With the syringe tip pointing down without plunger, cap the tip, fill the upright-syringe with water. Put the vial cap prepared in (a) on the water surface.
13 Part A: Preparation of Nitrogen Monoxide4. (c) Uncap the syringe to allow water to drain out from the syringe. After water drains out completely, the vial cap should sit at the bottom inside the syringe. From now on, always keep the syringe in an up-right position with tip pointing down.
14 Part A: Preparation of Nitrogen Monoxide5. Insert the plunger into the syringe with the tip of the plunger touching the vial cap, and draw about 4 cm3 of acidified FeSO4(aq) into the syringe. 6. Cap the syringe immediately.
15 Part A: Preparation of Nitrogen Monoxide7. Shake the syringe gently to mix the NaNO2(s) and the acidified FeSO4(aq). To prevent the reaction from going too fast, you should stop shaking when the reaction goes. Only when the reaction stops or goes slowly should you shake the syringe again. In case the amount of the nitrogen monoxide gas generated is more than the syringe can contain, let the plunger move out of the syringe (but with your hand holding the plunger to avoid falling) and allow excess gas to escape from the syringe.
16 Part A: Preparation of Nitrogen Monoxide8. When the production of NO(g) is finished, hold the plunger and remove the syringe cap carefully. Discharge the solution inside the syringe into the 1M NaOH solution.
17 Part A: Preparation of Nitrogen Monoxide9. To wash away the contaminants from the collected NO(g) with deionised water, draw about 10 cm3 of deionised water into the syringe. Cap the syringe again and shake or swirl the syringe to wash the gas inside the syringe. Remove the cap and discharge the water from the syringe into the 1M NaOH solution.
18 Part A: Preparation of Nitrogen Monoxide10. Repeat step 9 for 2 to 3 times Cap the syringe with the syringe cap, and the preparation of NO(g) is done.
19 Part B: Study of the Oxidising and Reducing Properties of Nitrogen Monoxide1. Add 5 cm3 of acidified KMnO4(aq), Br2(aq), and acidified FeSO4(aq) to 3 test tubes respectively.
20 Part B: Study of the Oxidising and Reducing Properties of Nitrogen Monoxide2. Inject a small amount of nitrogen monoxide from the syringe into each of the solutions. 3. With NO(g) left in the syringe, suck in small amount of air into the syringe by pulling the plunger slowly.
21 Results Record your observations in the table: ObservationsObservations Appearance of the solid NaNO2. Appearance of the acidified FeSO4 solution. Mixing NaNO2(s) with acidified FeSO4 solution. Washing NO(g) with deionised water. Appearance of NO(g). Before and after adding NO(g) to (1) acidified KMnO4(aq). (2) Br2(aq). (3) acidified FeSO4(aq). After mixing NO(g) with air (O2(g)).
22 Results Answer the questions after the experiment:1. In the reaction between NaNO2(s) and FeSO4(aq)/H+(aq), (a) which one is the limiting reagent? Given: The FeSO4 solution is prepared by dissolving 33.8 g of FeSO4·7H2O in 90 cm3 of water, followed by addition of 10 cm3 of concentrated sulphuric acid. (b) calculate the theoretical volume of NO(g) produced. Assume the gas is produced under room temperature and pressure. (c) which one is the oxidising reagent and which one is the reducing reagent? Explain your answer in terms of the changes in oxidation numbers. (d) Write down the half-equations for the oxidation and reduction occurred in the reaction between NaNO2(s) and FeSO4(aq)/H+(aq). (e) What is the observable change occurred in the reaction between NO(g) and FeSO4(aq)/H+(aq)? Write a balanced equation for the reaction. 2. What is the observable change occurred in the reaction between NO(g) and acidified KMnO4(aq)? Write a balanced equation for the reaction. 3. What is the observable change occurred in the reaction between NO(g) and Br2(aq)? Write a balanced equation for the reaction. 4. What is the observable change occurred in the reaction between NO(g) and O2(g)? Write a balanced equation for the reaction.
23 Making of Silver NanoparticlesCurriculum Link Topic XIV Materials Chemistry
24 Background Nanomaterials are organic or inorganic materials that have particle sizes below nm, they have properties that are very different from those of the bulk materials. For example, silver is a metal. It has a silvery and metallic appearance When dispersed in water, very fine powder of silver material looks grey (‘D’ in the figure) But the colour of silver nanoparticle is yellow or bright yellow (‘A’ in the figure).
25 Making of Silver NanoparticlesSodium borohydride acts as a reducing agent to reduce the Ag+ ions into silver metal. Silver nanoparticles are formed, and then stabilised by sodium borohydride, further growing to particles with bulk size is suppressed (∵repulsive electrostatic forces).
26 Different stages of aggregationBy changing the size, shape, composition and the level of aggregation of the nanoparticles, the light absorbing and scattering properties, and so the perceived colour can be tuned accordingly. Increasing the level of aggregation of silver nanoparticles
27 Tasks To synthesise silver nanoparticles from silver nitrate solution and sodium borohydride solution. To observe the colour of the solution of the silver nanoparticles. To study the aggregation of the silver nanoparticles in the solution prepared.
28 Chemicals M AgNO3(aq) M NaBH4(aq) Saturated NaCl(aq)
29 Part A: Synthesis of Silver Nanoparticles1. Use a measuring cylinder to measure 30 cm3 of M sodium borohydride solution, and pour the solution into a 100 cm3 beaker. 2. Place the beaker into an ice bath. Cool the solution in the ice bath for about minutes.
30 Part A: Synthesis of Silver Nanoparticles3. Use a clean measuring cylinder to measure 10 cm3 of M AgNO3 solution and transfer the solution into a burette. 4. Stir the NaBH4 solution in the beaker with a magnetic stirrer bar or a glass rod.
31 Part A: Synthesis of Silver Nanoparticles5. With the beaker containing NaBH4 solution still in the ice bath, add the AgNO3 solution dropwise from the burette to the NaBH4 solution in the beaker with continuous stirring, at a rate of about 1 drop per second, until the silver nitrate solution is used up. 6. Stop the stirring as soon as the addition of silver nitrate solution is finished, and remove the stirrer bar or glass rod from the mixture.
32 Part B: Study the Properties of the Silver Nanoparticles1. Right after the silver nanoparticles are prepared, place the beaker containing the nanoparticles and a 100 cm3 beaker containing about 40 cm3 water side by side. 2. Turn on a laser pointer from sideway such that the laser beam goes through both the solutions in the beakers.
33 Part B: Study the Properties of the Silver Nanoparticles3. Transfer about half of the silver nanoparticle solution into another 100 cm3 beaker, add about 10 cm3 of saturated NaCl solution into the beaker.
34 Results Record your observations in the table: ObservationsAppearance of the M silver nitrate solution. Appearance of the M sodium borohydride solution. Addition of AgNO3 solution to the NaBH4 solution. When the addition of AgNO3 solution is finished. When the laser beam goes through the water in beaker. When the laser beam goes through the silver nanoparticle solution in beaker. When NaCl solution is added to the silver nanoparticle solution.
35 Results Answer the questions after the experiment:1. What is the oxidation number of silver in (a) silver nitrate and (b) silver nanoparticles? 2. Write a half equation for Ag in the reaction. 3. What is/are the role(s) of NaBH4 in the solution? 4. State, with explanation, one important precaution when using NaBH4. 5. Is there any observed difference when a laser beam goes through the silver nanoparticle solution in beaker and water in beaker. Explain the difference(s) if any. 6. Explain why silver nanoparticles give a colour. 7. Explain why the bright yellow silver nanoparticles turn into gray precipitates when sodium chloride solution is added.
36 Solution v.s. colloid v.s. suspensionProperty Solution Colloid Suspension Particle size Less than 1 nm 1 to 100 nm Moe than 100 nm Homogeneity Homogeneous Homogeneous or heterogeneous Heterogeneous Transparency Transparent Often translucent and opaque but can be transparent Often opaque but can be translucent Separation Does not separate Separates or settles Filterability Passes through filter paper Particles do not pass through filter paper Examples Salt solution Milk Muddy water In this experiment, a colloid is formed in which insoluble silver nanoparticles are dispersed uniformly throughout the solution.
37 Curriculum Link Topic IV Acids and BasesQuantitative Analysis of a Mixture of Carbonates (Inquiry-Based Approach) Curriculum Link Topic IV Acids and Bases
38 Background You are given a sample of white powder. It is a mixture of potassium carbonate and calcium carbonate, but the percentages of the two compounds are not known.
39 Tasks To propose an experimental method to determine the ratio of potassium carbonate and calcium carbonate present in an unknown sample. To carry out an experiment to find out the ratio of potassium carbonate and calcium carbonate in the mixture. To compare and discuss the results obtained from other students or groups who carry out the determination with different methods.
40 Apparatus provided Filter funnel White tile Glass rod Hot plate100 cm3 Beaker 250 cm3 Beaker 250 cm3 Conical flasks 50 cm3 Pipette Burette 50 cm3 Measuring cylinder White tile Hot plate Stirrer bar Spatula Electronic balance Oven Filter papers Disposable droppers
41 Chemicals provided 0.200 M standard HCl(aq) 1.000 M standard HCl(aq)0.200 M standard NaOH(aq) 1.0 M BaCl2(aq) Methyl orange indicator Phenolphthalein indicator Deionised water Sample (Mixture of potassium and calcium carbonates)
42 Results Method Mass % of K2CO3 Mass % of CaCO3 1 2A 2B3 (Direct Titration) 4 (Back Titration)
43 Discussions What is your experimental method?What are the advantages and disadvantages of your experimental method? Why do you choose to carry out this experimental method? Are there any experimental errors/difficulties encountered in your experiment?
44 Possible Methods Method 1 (Measure the mass of insoluble CaCO3 residue after filtration) Method 2A (Precipitation between BaCl2 and filtrate) Method 2B (Titration between filtrate and standard strong acid) Method 3 (Direct Titration) Method 4 (Back Titration)
45 Method 1 (Measure the mass of insoluble CaCO3 residue)Potassium carbonate is soluble in water; calcium carbonate is insoluble. To find out the mass of calcium carbonate in the sample. Mixture of K2CO3 and CaCO3 Mixture of K2CO3 and CaCO3 Dissolve in water, Filtration Dissolve in water, Filtration CaCO3(s) (residue) CaCO3 (s) (residue) K2CO3 (aq) (filtrate) K2CO3(aq) (filtrate) Excess BaCl2(aq), Filtration Titrate against standard strong acid Titrate against standard strong acid Dry and weigh the insoluble CaCO3 Dry and weigh Dry and weigh the insoluble BaCO3 Dry and weigh the insoluble BaCO3 No. of mole of CO32-in K2CO3 No. of mole of CO32-in K2CO3
46 Method 2A (Precipitation between BaCl2 and filtrate)Barium carbonate is insoluble. To find out the amount of carbonate ions in soluble potassium carbonate. Mixture of K2CO3 and CaCO3 Mixture of K2CO3 and CaCO3 Dissolve in water, Filtration Dissolve in water, Filtration CaCO3(s) (residue) CaCO3 (s) (residue) K2CO3 (aq) (filtrate) K2CO3(aq) (filtrate) Excess BaCl2(aq), Filtration Titrate against standard strong acid Titrate against standard strong acid Dry and weigh the insoluble CaCO3 Dry and weigh Dry and weigh the insoluble BaCO3 Dry and weigh the insoluble BaCO3 No. of mole of CO32-in K2CO3 No. of mole of CO32-in K2CO3
47 Remarks on Method 1 and 2A For convenience, it is advised to weigh the filter paper before carrying out the filtration, and then weigh the total mass of the filter paper and residue after filtration and drying. The mass of residue can be determined from the difference between the two mass readings. Collect the residue from the filter paper and then weigh the residue collected will induce a large experimental error because a lot of residue would stick firmly on the filter paper. To increase the accuracy of the results, it is advised to heat the residue on filter paper in an oven at 110oC for at least 30 minutes before weighing, to ensure the residue and the filter paper are dried completely.
48 Method 2B (Titration between filtrate and standard strong acid)To find out the amount of carbonate ions in soluble potassium carbonate Use methyl orange as the indicator. Mixture of K2CO3 and CaCO3 Mixture of K2CO3 and CaCO3 Dissolve in water, Filtration Dissolve in water, Filtration CaCO3(s) (residue) CaCO3 (s) (residue) K2CO3 (aq) (filtrate) K2CO3(aq) (filtrate) Excess BaCl2(aq), Filtration Titrate against standard strong acid Titrate against standard strong acid Dry and weigh the insoluble CaCO3 Dry and weigh Dry and weigh the insoluble BaCO3 Dry and weigh the insoluble BaCO3 No. of mole of CO32-in K2CO3 No. of mole of CO32-in K2CO3
49 Method 3 (Direct titration)To find out the total amount of carbonate ions present in the sample. Use methyl orange as the indicator. Mixture of K2CO3 and CaCO3 Dissolve in water K2CO3(aq) + CaCO3(s) Titrate against standard strong acid Known amount of excess strong standard acid HCl Total amount of carbonate ions KCl(aq) + CaCl2(aq) + acid Titrate against standard alkali Total amount of carbonate ions
50 Method 4 (Back titration)To find out the total amount of carbonate ions present in the sample. Use phenolphthalein as the indicator. Mixture of K2CO3 and CaCO3 Dissolve in water K2CO3(aq) + CaCO3(s) Titrate against standard strong acid Known amount of excess strong standard acid HCl Total amount of carbonate ions KCl(aq) + CaCl2(aq) + acid Titrate against standard alkali Total amount of carbonate ions
51 Remarks on Methods 3 and 4 For methods 3 (direct titration), the determination of end-point is difficult due to various reasons, such as the poor solubility of calcium carbonate in water. However, the accuracy of this method is comparable with other methods so it is not excluded. Back titration technique is not required in DSE Chemistry curriculum, but its determination of end-point was easier in our trials.
52 Other methods measuring volume of CO2(g) producedResults are not satisfactory, due to reasons like the leakage of gas and the solubility of CO2(g) in solution. These two methods are not recommended. Mixture of K2CO3 and CaCO3 + HCl KCl(aq) + CaCl2(aq) +H2O(l) + CO2(g) Measure the volume of CO2 gas produced Measure the loss of mass in the sample due to the loss of CO2 gas
53 Summary of results Method Mass % of K2CO3 Mass % of CaCO3 1 64 36 2A50 2B 55 45 3 (Direct Titration) 62 38 4 (Back Titration) 63 37
54 Solving simultaneous linear equations in 2 unknowns