Experimental Chemistry Parts I and II PDF

Experimental Chemistry SIO LEARNING OUTCOME SUCCESS CRITERIA Candidates should be able to: 1.1a name appropriate apparatus for the measurement of Unfamiliar 1. I am able to state the appropriate apparatus time, temperature, mass...

Experimental Chemistry SIO LEARNING OUTCOME SUCCESS CRITERIA Candidates should be able to: 1.1a name appropriate apparatus for the measurement of Unfamiliar 1. I am able to state the appropriate apparatus time, temperature, mass and volume; including for the measurement of burettes, pipettes, measuring cylinders and gas (i) time; (ii) temperature; (iii) length; (iv) mass ; (v) volume syringes of gas Unfamiliar 2. I am able to state the appropriate apparatus for the measurement of volume of liquids based on the volume of liquid and accuracy required 1.1b suggest suitable apparatus, given relevant information, Unfamiliar 3. I am able to suggest appropriate for a variety of simple experiments, including drying apparatus and drying agent for the collection of gas, given agents and collection of gases and measurement of information of how the gas reacts with concentrated sulfuric rates of reaction (drying agents will be limited to acid, calcium oxide or fused calcium chloride calcium oxide, concentrated sulfuric acid and fused calcium chloride) Unfamiliar 4. I can suggest appropriate apparatus for gas collection based on the solubility of gas in water and/or density of gas 1.2a describe methods of separation and purification for the Unfamiliar 5. I am able to list the apparatus used with a components of mixtures, to include: separating funnel to separate immiscible liquids. use of a suitable solvent, filtration and crystallisation or evaporation Unfamiliar 6. I am able to list the apparatus used in sublimation filtration. distillation and fractional distillation (see also 11.1(b)) use of a separating funnel Unfamiliar 7. I am able to list the apparatus used in paper chromatography evaporation as a separation technique. Unfamiliar 8. I am able to list the apparatus used in distillation. Unfamiliar 9. I am able to list the apparatus used in fractional distillation. Unfamiliar 10. I am able to list the apparatus used in crystallisation. Unfamiliar 11. I am able to list the apparatus used in chromatography. Unfamiliar 12. I am able to list the apparatus used for sublimation as a separation technique. Unfamiliar 13. I am able to explain the requirements of distillation and fractional distillation (e.g. position of apparatus, when a fractionating column is used) Unfamiliar 14. I am able to explain the requirements of chromotagraphy (e.g. drawing of the starting line in pencil) Unfamiliar 15. I am able to explain the requirements of crystallisation (e.g. heat until saturation, cool, filter and dry) Unfamiliar 16. I am able to explain the principle(s) behind the use of a separating funnel –miscibility of liquids (not differences in densities) Unfamiliar 17. I am able to explain the principle(s) behind filtration – difference in solubility in the solvent used / difference in particle size of solutes Unfamiliar 18. I am able to explain the principle(s) behind evaporation - difference in boiling point of dissolved solute and solvent Unfamiliar 19. I am able to explain the principle(s) behind distillation – selective condensation due to differences in boiling points Unfamiliar 20. I am able to explain the principle(s) behind crystallisation – a. dissolving excess solute at a higher temperature and cooling such that the solubility decreases, b. crystallisation allows for a pure substance free from soluble impurities to be formed. Unfamiliar 21. I am able to explain the principle(s) behind chromatography – different components have different solubility, hence different Rf values, in the specified  solvent Unfamiliar 22. I am able to explain the principle(s) behind sublimation - ability of one solid to change directly into a gas upon heating. 1.2b suggest suitable separation and purification methods, Unfamiliar 23. I am able to state whether a solid given information about the substances involved in the dissolves when a solvent is added to a mixture to 2 solids following types of mixtures: based on their solubility in the solvent. solid-solid solid-liquid Unfamiliar 24. I am able to state the products of a liquid-liquid (miscible and immiscible) mixture after separation (via filtration, evaporation distillation) Unfamiliar 25. I am able to suggest the appropriate separation technique(s) to separate 2 or more substances based first on the (i) physical state of the substances relative to one another (solid-solid, liquid-liquid, solid-liquid); (ii) soluiblity of the solid in the solvent for solid-liquid mixtures and miscibility of the substances in liquid-liquid mixtures. Unfamiliar 26. I am able to state the sequence in which to apply the separation techniques (if there is more than 1 technique involved) to separate 2 or more substances. 1.2c interpret paper chromatograms including comparison Unfamiliar 27. I am able to calculate Rf values using the with ‘known’ samples and the use of Rf values distances travelled by the solvent and substance Unfamiliar 28. I am able to identify the components in an unknown substance by comparing their Rf values with Rf values of known substances 1.2d explain the need to use locating agents in the Unfamiliar 29. I am able to explain the need to use chromatography of colourless compounds (knowledge locating agents in the chromatography of colourless of specific locating agents is not required) compounds. 1.2e deduce from given melting point and boiling point data Unfamiliar 30. I am able to describe how the identities of substances and their purity chromatography and the checking of a melting point of a solid (or boiling point of a liquid) are used to determine the purity of a substance Unfamiliar 31. I am able to describe the difference in melting point and boiling point of an impure substance compared to a pure substance Unfamiliar 32. I am able to state the physical state of a substance given its melting and boiling point 1.2f explain the importance of measuring the purity in Unfamiliar 33. I am able to explain the importance of substances used in everyday life, e.g. foodstuffs and measuring the purity in substances such as foodstuffs and drugs drugs. Experimental Chemistry Part I - Experimental Design  Key Concept A: Measuring Physical Quantities 1. Measuring Mass a. The S.I. unit for mass is the kilogram (kg). b. Other commonly used units are gram (g) and tonne (t). c. The electronic balance is used for precise and fast weighing of small amounts of substances with an accuracy of up to ±0.01 g. 2. Measuring Time a. The S.I. unit for time is the second (s). b. Other commonly used units are minute (min) and hour (h). c. The digital stopwatch is used for measuring time to an accuracy of ±0.01 s 3. Measuring Temperature a. The S.I. unit for temperature is kelvin (K). b. The other commonly used unit is degree Celsius (°C) c. Temperature in K = Temperature in °C + 273 d. The mercury and alcohol thermometers are used to measure temperature of liquids or reaction mixture. They usually measure temperatures ranging from – 10°C to 110°C. e. Measure temperature to an accuracy of ±0.5°C. f. A data logger connected to a temperature sensor can also be used to measure temperature. g. It is more accurate than the thermometers and can record data continuously over a period of time. 4. Measuring Volume a. The S.I. unit for volume is cubic metre (m3). b. Other commonly used units are cubic centimetre (cm3) and cubic decimetre (dm3). c. Measure volumes of liquids Measuring cylinder: measure up to the nearest 0.1 cm3.​ *dependent on instrument graduation (half of the smallest increment) Burette: accurately measures variable volumes of liquid to the nearest 0.05 cm3. Pipette: accurately measures fixed volume of liquid e.g. 10.0 cm3, 25.0 cm3. d. Measure volumes of gases The gas syringe is commonly used to measure volume of gas. It measures a maximum volume of 100 cm3. Self-Assessment Questions: Measuring Physical Quantities 1. A student plans to dissolve 4.08g of solid sucrose in 43.00 cm3 of distilled water. ​ List the pieces of apparatus that should be used to ensure that this is done accurately. __________________________________________________________________________________________​ 2. A beaker of water is heated to 63°C. Calculate this temperature in kelvin (K). 3. In an experiment, 50 cm3 of hydrochloric acid was added to 4.00 g of solid sodium carbonate in a conical flask, to produce carbon dioxide gas. The time taken to collect 5 cm3 of gas was measured.​ List all the pieces of apparatus required for this experiment. __________________________________________________________________________________________​ ​ __________________________________________________________________________________________ __________________________________________________________________________________________ Key Concept B: Methods of Collecting and Drying Gases 1. Methods for Collecting Gases The method for collection of gas depends on: solubility of the gas in water density of the gas, compared to air a. Downward displacement of water For collecting gases that are insoluble or slightly soluble in water. E.g. carbon dioxide, oxygen, hydrogen b. Downward delivery of gas For collecting gases that are soluble in water and denser than air E.g. chlorine, hydrogen chloride, sulfur dioxide c. Upward delivery of gas For collecting gases that are soluble in water and less dense than air.  E.g. ammonia 2. Drying gases Pass the moist gas through a drying agent. a. Drying with concentrated sulfuric acid b. Drying with quicklime (calcium oxide) c. Drying with fused calcium chloride​ *fused calcium chloride cannot be used to dry ammonia​ (ammonia forms a ammine complex with calcium ions - explanation not in syllabus) Self-Assessment Questions: Methods of Collecting and Drying Gases 1. The table below contains some qualitative data on the solubility and density of some gases. ​ Fill in the table with the most suitable methods of collecting these gases. Gas Solubility Density compared to air Method of collection Hydrogen Not soluble Less dense Oxygen Slightly soluble Slightly denser Carbon dioxide Slightly soluble Denser Chlorine Soluble Denser Hydrogen Very soluble Denser chloride Sulfur dioxide Very soluble Denser Ammonia Very soluble Less dense Experimental Chemistry Part II - Methods for Separation and Purification Key Concept A: Paper Chromatography 1. Paper chromatography can be used to a.​ separate the components of a mixture, e.g. dyes, amino acids. b.​ identify the components of a mixture. c.​ test the purity of a substance. 2. Principles of chromatography a.​ As the solvent travels up the paper, the components of the mixture dissolve and move with it. b.​ Since different components have different solubility in the solvent, they travel up at different speeds. c.​ The most soluble component travels the fastest and furthest. d.​ Identical substances travel the same distance (under the same solvent). 3. The unknown spots can be identified by their Rf values. 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑚𝑜𝑣𝑒𝑑 𝑏𝑦 𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡 𝑥 Rf = 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑚𝑜𝑣𝑒𝑑 𝑏𝑦 𝑠𝑜𝑙𝑣𝑒𝑛𝑡 , e.g. Rf value for component B = 𝑦 4. Advantage of paper chromatography Identification of small quantities of both coloured and colourless substances. 5. Use of locating agents a.​ A locating agent is used to determine the positions of colourless spots, e.g. amino acids, on the chromatogram. b.​ When the locating agent is sprayed on the chromatogram, it reacts with the colourless components to form coloured spots, hence enabling the positions of the colourless spots to be seen. Self-Assessment Questions: Paper chromatography 1. The diagram below shows a chromatogram obtained using solutions of three single dyes (blue, green and red) and four other solutions (A, B, C and D). The solvent used is water. (a) Which of the solutions A, B, C or D contains the following: (i) a pure dye?​ ​ ​ ​ _______________ (ii) green and red dyes only?​ ​ _______________ (iii) a dye other than blue, green and red?​ _______________ (b) Calculate the Rf value of the blue dye. (c) If ethanol is used as the solvent (instead of water), would you expect the Rf value of the blue dye to be the same as the one calculated in (b). Explain. (d) Explain why it is important for each of the following to be carried out in the chromatography. (i) The start line must not be drawn in ink. (ii) The mixture samples on the start line must be as small as possible. Key Concept B: Methods of separation 1. The methods of separation are: (i)​ Evaporation (ii)​ Crystallisation (iii)​ Filtration (iv)​ Sublimation (v)​ Simple distillation (vi)​ Fractional distillation (vii)​ Using a separating funnel 2. Separating a solute (soluble solid) from a solution (a) Evaporation To obtain a solute from a solution (b) Crystallisation To obtain a solute (which decomposes on heating) from a solution 3. Separating a mixture of solids (a) Filtration (i)​ To separate a mixture of a solid and a liquid ​ ​ ​ (ii)​ To separate a mixture of two solids (b) Sublimation To separate a mixture of two solids (one of which sublimes on heating). ​ ​ Examples of solids that sublime on heating: iodine, ammonium chloride and carbon dioxide. 4. Separating a liquid from a solution / liquid mixture (a) Simple distillation To obtain a liquid from a solution (b) Fractional distillation To separate a mixture of miscible liquids, i.e. liquids that mix completely. (c) Using a separating funnel To separate a mixture of immiscible liquids, i.e. liquids that do not mix. Self Assessment Questions: Methods of separation 1. Some countries grow sugar cane from which sugar is extracted. The sugar can be extracted on a laboratory scale by cutting the cane into pieces, crushing it and stirring it with water to dissolve the sugar. (a) Draw a labelled diagram of the apparatus that can be used in the laboratory to separate the pieces of crushed cane from the sugar solution. (b) Describe the method to obtain crystals of sugar from the sugar solution. (c) How does temperature affect the solubility of sugar in water? (d) How does the rate of cooling affect the size of crystals formed? (e) What happens if solutions of sugar or copper (II) sulfate are heated till dryness? 2. The following diagram represents an apparatus used to distil seawater. (a) Why is the bulb of the thermometer placed at the outlet to the condenser? (b) Does the cooling water enter the condenser at A or B? Explain why. (c) What is the purpose of adding a few antidumping granules into the distillation flask? (d) How would you modify the apparatus so that a flammable liquid can be purified? (e) To distill a solution of ethanol in water, a fractionating column is added. The boiling points of ethanol and water are 78°C and 100°C respectively. Describe how this separation technique works. Key Concept C: Criteria for Purity 1. There are only two ways to determine the purity of a substance: a.​ Melting / boiling point of the substance b.​ Chromatography 2. The purity of a solid can be tested by determining its melting point. a.​ A pure solid melts at a fixed melting point. b.​ An impure solid melts over a range of temperatures below the melting point of the pure solid. 3. The purity of a liquid can be tested by determining its boiling point. a. A pure liquid boils at a fixed boiling point. b. An impure liquid boils over a range of temperatures above the boiling point of the pure liquid. 4. The purity of a substance can also be determined by chromatography. a.​ If a substance is pure, its chromatogram should show only 1 distinct spot. b.​ If a substance contains impurities, its chromatogram would show 2 or more faint spots. c.​ Chromatography can be used to detect small quantity of impurities. 5. Ensuring the purity of substances is important in everyday life. a.​ In the electronic industry, purity ensures the effectiveness of components in electrical devices. b.​ In the food and beverage industry, purity ensures safety of chemicals added to food and drinks for consumption. c.​ In the pharmaceutical industry, purity ensures the original properties of the medicine and avoids undesirable side effects upon consumption. Self-Assessment Questions: Criteria for Purity 1. Esters are colourless liquids with a fragrant smell. They are immiscible with water. Which property of an ester could be used to check its purity before it is used as a food flavouring? A Boiling point B Colour C Smell D Solubility in water 2. The melting points of mixtures of lead and tin are shown in the graph below. The graph shows that any mixture of lead and tin must have a melting point ___________________. A above that of tin B below that of lead C below that of both lead and tin D between that of lead and tin 3. Urea, used extensively as a fertiliser, has a melting point of 133°C. It was found that a mixture of urea and compound X has a melting point of 133°C. Another mixture of urea and compound Y was found to melt at around 129°C. What can you deduce about compounds X and Y?