Alternative to Practical Paper 6 TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 1 of 21 Pursuit of Excellence Experimental techniques and chemical analysis Syllabus: Experiment 1: Experimental design I. Name appropriate apparatus for the measurement of time, temperature, mass and volume, including: a) stop-watches b) thermometers c) balances d) burettes e) volumetric pipettes f) measuring cylinders g) gas syringes II. Suggest advantages and disadvantages of experimental methods and apparatus Experiment 2: Experimental design Describe a: a) solvent as a substance that dissolves a solute b) solute as a substance that is dissolved in a solvent c) solution as a liquid mixture composed of two or more substances d) saturated solution as a solution containing the maximum concentration of a solute dissolved in the solvent at a specific temperature e) residue as a substance that remains after evaporation, distillation, filtration or any similar process f) filtrate as a liquid or solution that has passed through a filter Experiment 3: Chromatography I. Describe how paper chromatography is used to separate mixtures of soluble coloured substances, using a suitable solvent II. Interpret simple chromatograms to identify: a) unknown substances by comparison with known substances b) pure and impure substances III. State and use the equation for Rf: Rf = distance travelled by substance / distance travelled by solvent IV. Describe how paper chromatography is used to separate mixtures of soluble colourless substances, using a suitable solvent and a locating agent Knowledge of specific locating agents is not required Experiment 4: Separation and Purification: I. Describe and explain methods of separation and purification using: a) a suitable solvent b) filtration c) crystallisation d) simple distillation e) fractional distillation II. Suggest suitable separation and purification techniques, given information about the substances involved TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 2 of 21 Pursuit of Excellence III. Identify substances and assess their purity using melting point and boiling point information Experiment 5: Preparation of salts: I. Describe the general solubility rule for salts: a) sodium, potassium and ammonium salts are soluble b) nitrates are soluble c) chlorides are soluble, except lead and silver d) sulphates are soluble, except barium, calcium and lead e) carbonates and hydroxides are insoluble, except sodium, potassium and ammonium f) hydroxides are insoluble, except sodium, potassium, ammonium and calcium (partially) II. Describe tests to identify the anions: a) carbonate, CO32–, by reaction with dilute acid and then testing for carbon dioxide gas b) chloride, Cl–, bromide, Br–, and iodide, I–, by acidifying with dilute nitric acid then adding aqueous silver nitrate c) nitrate, NO3–, by reduction with aluminium and aqueous sodium hydroxide and then testing for ammonia gas d) sulphate, SO42–, by acidifying with dilute nitric acid then adding aqueous barium nitrate e) sulphite, SO32–, by reaction with acidified aqueous potassium manganate (VII) III. Describe the use of a flame test to identify the cations: (a) lithium, Li+ (b) sodium, Na+ (c) potassium, K+ (d) calcium, Ca2+ (e) barium, Ba2+ (f) copper(II), Cu2+ IV. Describe tests using aqueous sodium hydroxide and aqueous ammonia to identify the aqueous cations: a) aluminium, Al3+ b) ammonium, NH4+ c) calcium, Ca2+ d) chromium(III), Cr3+ e) copper(II), Cu2+ f) iron(II), Fe2+ g) iron(III), Fe3+ h) zinc, Zn2+ V. Describe tests to identify the gases: a) ammonia, NH3, using damp red litmus paper b) carbon dioxide, CO2, using limewater c) chlorine, Cl2, using damp litmus paper d) hydrogen, H2, using a lighted splint e) oxygen, O2, using a glowing splint f) sulfur dioxide, SO2, using acidified aqueous potassium manganate (VII) Experiment 6: Water I. Describe chemical tests for the presence of water using anhydrous cobalt(II) chloride and anhydrous copper(II) sulfate II. Describe how to test for the purity of water using melting point and boiling point III.Explain that distilled water is used in practical chemistry rather than tap water because it contains fewer chemical impurities. TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 3 of 21 Pursuit of Excellence Experimental design 1 Video Link: Making measurements in Chemistry: https://www.youtube.com/watch?v=zuPCBtiWRM4 Lab equipment: Link 1: https://www.youtube.com/watch?v=G36K4UDZLLo Link 2: https://www.youtube.com/watch?v=pAcPs5yXAC4 Measurement of Length A measuring scale is used to measure the length of an object. The unit of length is the metre (m) We do most measurement in centimetre (cm). The 1m = 100cm, 1cm = 10mm A measuring scale Measurement of Mass A balance is used to measure the mass of an object. The unit of mass is the kilogram (kg). The gram (g) is one-thousandth of a kilogram: 1 g = 1/1000 kg = 10-3 kg = 0.001 kg A balance can have an analogue and digital versions An analogue balance A digital balance Some other types of balances, commonly used are: TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 4 of 21 Pursuit of Excellence A beam balance A lever balance Measurement of Time Clocks, watches and timers can be used to measure time intervals. The unit of time is seconds (s). In an experiment it is important to choose the correct timing device for the required measurement. A stopwatch will be sufficient if a time in minutes or seconds is to be measured, but if times of less than a second are to be determined then a digital timer is necessary. Analogue stop watch Digital stop watch Measurement of Temperature A thermometer is used to measure temperature. The SI unit of temperature is Kelvin(K). o C(Celcius) and F(Fahrenheit) are other units of temperature. All these units are interconvertible. TK = TC + 273.15 TF = 1.8TC + 32 A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a mercury-in-glass thermometer or the pyrometric sensor in an infrared thermometer) in which some change occurs with a change in temperature; and (2) some means of converting this change into a numerical value (e.g. the visible scale that is marked on a mercury-in-glass thermometer or the digital readout on an infrared model). Thermometers are widely used in technology and industry to monitor processes in meteorology, medicine and scientific research. TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 5 of 21 Pursuit of Excellence An infrared thermometer Alcohol laboratory thermometer Clinical mercury thermometer Advantages of using an alcohol thermometer in lab. Unlike the mercury-in-glass thermometer, the contents of an alcohol thermometer are less toxic and will evaporate quickly. The ethanol version is the most widely used due to the low cost and relatively low hazard posed by the liquid in case of breakage. Measurement of Volume Various apparatus like graduated cylinder, pipette, burette, gas syringes etc can be used to measure volume. The unit of volume is Litre (L). The millilitre (ml) is one-thousandth of a Litre: 1 ml = 1/1000 L = 10-3 L= 0.001 L A graduated cylinder, also known as a measuring cylinder or mixing cylinder is a common piece of laboratory equipment used to measure the volume of a liquid. It has a narrow cylindrical shape. Each marked line on the graduated cylinder represents the amount of liquid that has been measured. A pipette is a laboratory tool commonly used in chemistry, biology and medicine to transport a measured volume of liquid. Pipettes come in several designs for various purposes with differing levels of accuracy and precision. They can be single piece glass or more complex adjustable or electronic pipettes. Many pipette types, work by creating a partial vacuum above the liquid-holding chamber and selectively releasing this vacuum to draw up and dispense liquid. Measurement accuracy varies greatly depending on the instrument. TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 6 of 21 Pursuit of Excellence Pipette Burette Reading miniscus A burette is a volumetric measuring glassware which is used in analytical chemistry for the accurate dispensing of a liquid, especially of one of the reagents in a titration. The burette tube carries graduated marks from which the dispensed volume of the liquid can be determined. Comparison of a burette to a pipette and graduated cylinder: Compared to a volumetric pipette, a burette has similar precision if used to its full capacity, but as it is usually used to deliver less than its full capacity, a burette is slightly less precise than a pipette. The burette is different from a measuring cylinder as its graduations measure from top to bottom. Therefore, the difference between the starting and the final volume is equal to the amount dispensed. The precision and control of the burette over other means of adding solution is beneficial for use in titration. How to read the volume accurately? To read the volume accurately, the observation must be at an eye level and read at the bottom of a meniscus of the liquid level. The main reason as to why the reading of the volume is done via meniscus is due to the nature of the liquid in a closed surrounded space. By nature, liquid in the cylinder would be attracted to the wall around it through molecular forces. This forces the liquid surface to develop either a convex or concave shape, depending on the type of the liquid in the cylinder. Reading the liquid at the bottom part of a concave or the top part of the convex liquid is equivalent to reading the liquid at its meniscus. From the picture, the level of the liquid will be read at the bottom of the meniscus, which is the concave. The most accurate of the reading that could be done here is reduced down to 1 mL due to the given means of measurement on the cylinder. From this, the derived error would be one tenth of the least figure. For instance, if the reading is done and the value calculated is set to be 36.5 mL. The error, give or take 0.1 mL, must be included too. For example, if the reading is done and the value calculated is set to be 40.0 mL. The precise value would be 40.0+ 0.1; 40.1 or 39.9 mL. A gas syringe is a piece of laboratory glassware used to insert or withdraw a volume of a gas from a closed system, or to measure the volume of gas evolved from a chemical reaction. When using a gas syringe to measure gases it is important to keep the syringe free from liquids. As gases can dissolve in liquids, especially under any resulting pressure, this may result in inaccurate measurements (Henry's law). A gas syringe can also be used to measure and dispense liquids, especially where these liquids need to be kept free from air. TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 7 of 21 Pursuit of Excellence Gas syringes come in various sizes from 500 ml to 0.25 ml and tend to be accurate to between 0.01 and 1 ml, depending on the size of the syringe. Gas syringe gas syringe in use Acid-Base titration: This is a quantitative analysis also called volumetric titration. This technique is often used to calculate the strength of acid or alkali. Here acid is taken in a burette and is called a titrant. A known volume of base is taken in a flask using a pipette and slowly and carefully, known volumes of acid is added from the burette. Addition of the acid continues till neutralization point is reached which is indicated by a colour change in the indicator. TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 8 of 21 Pursuit of Excellence Experimental design 2 Video link: Components of a solution: https://www.youtube.com/watch?v=qyUnRgzKci4 Residue and filtrate:https://www.youtube.com/watch?v=vr3n1fUa2Vg Solutions are homogeneous mixtures of two or more than two components. The component of the solution that is present in the largest quantity is known as solvent. The component that is present in the less quantity is known as solute. A solute is dissolved in a solvent. The solution consisting of two components is known as binary solution. SOLUBILITY • Solubility of a substance is its maximum amount that can be dissolved in a specified amount of solvent at a specified temperature. • It depends upon the nature of solute and solvent as well as temperature and pressure. Saturated Solution: A solution which has maximum amount of solute dissolved into it such that no more solute can be dissolved at a particular temperature. Unsaturated Solution: A solution which does not have the maximum amount of solute dissolved into it and more solute can be added to it at a particular temperature. A saturated solution can be made unsaturated by heating. Residue is the substance that is left behind after evaporation, distillation or filtration or any other similar process. Filtrate is the liquid or solution that has passed through a filter paper. For example: When a spoonful of salt is added to water and mixed: Solute: Salt Solvent: Water Solution: Mixture of salt and water When the solution of chalk powder in water is prepared and filtered: Residue: the chalk powder that is obtained on the filter paper. Filtrate: The water that is obtained after passing through the filter paper. TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 9 of 21 Pursuit of Excellence Chromatography Video Link: Paper chromatography Link 1: https://www.youtube.com/watch?v=FAN6kyZVQXo Link 2: https://www.youtube.com/watch?v=mz_xcNrTK_U Chromatography technique that uses paper sheets or strips as the adsorbent being the stationary phase through which a solution is made to pass is called paper chromatography. It was discovered by Synge and Martin in the year 1943. It is an inexpensive method of separating dissolved chemical substances by their different migration rates across the sheets of paper. It is a powerful analytical tool that uses very small quantities of material. Principle: When the mobile phase moves, the separation of the mixture takes place. The compounds in the mixture separate themselves based on the differences in their affinity towards stationary and mobile phase solvents under the capillary action of pores in the paper. Paper Chromatography Diagram Procedure: The following steps are followed during paper chromatography: 1. Selecting a suitable type of development: It is decided based on the complexity of the solvent, paper, mixture, etc. paper chromatography is used quite often as it is easy to perform and is less time-consuming. Also, it is easy to handle, the chromatogram obtained. 2. Selecting a suitable filter paper: Selection of filter paper is done based on the size of the pores and the sample quality. 3. Prepare the sample: Sample is prepared by dissolving the sample in a suitable solvent. 4. Spot the sample on the paper: Samples should be spotted at a proper position on the paper, using a capillary tube. 5. Chromatogram development: Chromatogram is immersed in the mobile phase. Due to the capillary action of paper, the mobile phase moves over the sample on the paper. 6. Paper drying and compound detection: Once the chromatogram is developed, the paper is dried using an air drier. Also, detecting solution can be sprayed on the chromatogram and dried to identify the sample chromatogram spots. TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 10 of 21 Pursuit of Excellence Applications: Some of the applications of paper chromatography are as follows: • To check the purity of pharmaceuticals. • To inspect cosmetics. • To detect the adulterants. • To detect the contaminants in drinks and foods. • To examine the reaction mixtures in biochemical laboratories. Limitations: Limitations of Paper Chromatography are as follows: • Paper chromatography cannot handle large amounts of sample. • Paper chromatography is ineffective in quantitative analysis. • Paper chromatography cannot separate complex mixtures. Interpreting a chromatogram Separation by chromatography produces a chromatogram. A paper chromatogram can be used to distinguish between pure and impure substances: • a pure substance produces one spot on the chromatogram • an impure substance produces two or more spots A paper chromatogram can also be used to identify substances by comparing them with known substances. Two substances are likely to be the same if: • they produce the same number of spots, and these match in colour • the spots travel the same distance up the paper compared to reference spots (have the same Rf value) Rf (Retention factor) values The Rf value of a spot is calculated using: Rf = distance travelled by substance / distance travelled by solvent • The Rf value is always the same for a particular substance using the same stationary phase and mobile phase. • Rf values can be used to identify unknown chemicals if they can be compared to a range of reference substances. • Rf values vary from 0 (the substance is not attracted to the mobile phase) to 1 (the substance is not attracted to the stationary phase). TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 11 of 21 Pursuit of Excellence Standard Rf values of some pigments Locating agent: A locating agent is used to analyse colourless substances in paper chromatography. It is generally a chemical that reacts with the colourless substances in order to form colourful products that are visible for inspection purpose. One such example of a locating agent is ninhydrin spray. TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 12 of 21 Pursuit of Excellence Separation and Purification Video links: Separation techniques Link 1: https://www.youtube.com/watch?v=KVcvIEZeNcA Separation techniques Link 2: https://www.youtube.com/watch?v=bkYqqJa5P8w Separating using suitable solvent: https://www.youtube.com/watch?v=XC1RxloV0Mo Filtration: https://www.youtube.com/watch?v=lrnt9QswVZ8 Crystallisation of Copper sulphate: https://www.youtube.com/watch?v=QdwKhbtzsug Distillation: https://www.youtube.com/watch?v=V5ep0-ojPGw Fractional distillation: https://www.youtube.com/watch?v=J1FjIRWVwTM Separation and purification mean separation of a substance into its components and the removal of impurities. There are a large number of important applications in fields such as medicine and manufacturing. • The petroleum industry separates crude oil into products used as fuels, lubricants, and chemical raw materials • The pharmaceutical industry separates and purifies natural and synthetic drugs to meet health needs • The mining industry is based on the separation and purification of metals. • In the field of medicine and the sciences. In the life sciences Reasons for making separations There are two general reasons for performing separations on mixtures. 1. The mixture may contain some substance (considered to be contaminants) that should be isolated from the rest of the mixture. This process of isolating and thus removing substances is called purification. 2. To alter the composition of a sample so that one or more of the components can be analyzed. Separation Techniques: Separation using suitable solvent: In some situations, one component of a combination is soluble in a liquid solvent while the other is not. This variation in solubilities can be utilised to separate the elements of a combination. For example, Sugar is soluble in water but sand is not, therefore a combination of sugar and sand may be separated using water as a solvent. Filtration is a physical separation process that separates solid matter and fluid from a mixture. The separation of solid and fluid is imperfect; solids will be contaminated with some fluid and filtrate will contain fine particles (depending on the pore size, filter thickness etc.) Evaporation is another physical process that separates soluble solid from a liquid. Here the mixture is boiled slowly to remove the liquid while the solid is left behind. For example, mixture of salt and water can be separated using evaporation. TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 13 of 21 Pursuit of Excellence Filtration Evaporation Crystallisation is the process by which a solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Crystallization is also a chemical solid–liquid separation technique. The process is related to precipitation. Crystallization is one of the purification techniques which follows the process of purification substances by removing unwanted by-products. The procedure of crystallization of copper sulphate: 1. Prepare a clear solution of copper sulphate. 2. Dissolve 0.8g of CuSO4.5H20 in about 8 mL of water and add 1-2 drops about 6 mL H2SO4 to it. 3. Heat the solution for a while and filter it using a filtration unit. 4. Transfer the solution from filtration unit to another beaker and allow it to cool to room temperature. 5. The crystals will appear. 6. Filter, wash these crystals and let it dry 7. Weigh the crystals and report the yield. . Distillation is a method of separation based on differences in the boiling points of substances. During distillation, the mixture is boiled; the component having lower boiling point gets converted to vapours which is condensed and collected separately. The two components are thus separated. TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 14 of 21 Pursuit of Excellence Distillation refers to the selective boiling and subsequent condensation of a component in a liquid mixture. It is a separation technique that can be used to either increase the concentration of a particular component in the mixture or to obtain (almost) pure components from the mixture. The process of distillation is based on the difference in the boiling points of the components in the liquid mixture by forcing one of them into a gaseous state. Distillation is not a chemical reaction but it can be considered as a physical separation process. Simple distillation Fractional distillation Fractional distillation is a type of distillation which involves the separation of miscible liquids. The basic principle of this type of distillation is that different liquids boil and evaporate at different temperatures. So, when the mixture is heated, the substance with lower boiling point starts to boil first and convert into vapours. The process involves repeated distillations and condensations and the mixture is usually separated into component parts. The separation happens when the mixture is heated at a certain temperature where fractions of the mixture start to vaporize. Distillation refers to the process of vaporisation followed by condensation (liquefaction). When this distillation process is repeated, a more volatile component will remain in a pure state in the liquid state. By using the fractional distillation method, components of the liquid-liquid mixture can be separated as a pure substance. Separation of Immiscible liquids: Immiscible liquids can be separated using separating funnel. The mixture is poured into the separating funnel and the layers are allowed to separate. The lower layer can be run off by opening the tap of the separating funnel. Separation using separating funnel TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 15 of 21 Pursuit of Excellence Preparation of salts The general solubility rule for salts are as follows: Soluble salts • • • • • • Insoluble salts All salts of Sodium, Potassium and Ammonium are soluble All Nitrates are soluble All chlorides except lead and silver chlorides Barium, Calcium and lead sulfates, all sulphates are soluble. Sodium, Potassium and Ammonium carbonates and hydroxides Calcium hydroxide • Lead and Silver chloride • Barium, Calcium and lead sulfates, all ine soluble. All carbonates and hydroxides except Sodium, Potassium and Ammonium carbonates and hydroxides. • Identification on the basis of appearance or smell: A preliminary examination helps in identification of substance. Deduction on the basis of appearance or smell Observation on substance Black powder Pale green crystals Dark green crystals Blue or blue-green crystals Yellow-brown crystals Smell of ammonia Indication Carbon, CuO or CuS Contains Fe2+ ions Contains Ni2+ ions Contains Cu2+ ions Contains Fe3+ ions Contains NH4+ ions Test to identify the anions: Experiment Observation Inference Test for carbonate, CO32– To the carbonate salt add dil. H2SO4, and allow the gas produced to pass through lime water Colourless gas is produced with effervescence. Lime water turns milky Carbonate, CO32– confirmed Test for chloride, Cl–, bromide, Br–, and iodide, I– To aqueous solution of the halide salt. Add dil. HNO3 and aqueous silver nitrate. Cl- gives a white precipitate Chloride, Cl- confirmed Bromide, Br- confirmed Br- gives a cream precipitate Iodide, I- confirmed I- gives a yellow precipitate TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 16 of 21 Pursuit of Excellence Test for nitrate, NO3– To aqueous solution of the nitrate salt add aqueous sodium hydroxide, then aluminium foil, warm carefully. Test for sulphate, SO42– Make aqueous solution of the halide salt. Add dil. HNO3 and aqueous barium nitrate. A colourless gas with a foul smell (ammonia) is produced. Nitrate NO3- confirmed White precipitate of Barium sulphate is produced. Sulphate, SO42– confirmed Test for sulphide, SO32– To the sulphide salt add acidified acidified aqueous potassium manganate (VII) The colour of acidified acidified aqueous potassium manganate (VII), changes from purple to colourless. Sulphite, SO32– confirmed Test to identify the cations using Flame test: Some metal ions can be detected by observing the colour of the flame produced, by soaking a wooden splint in aqueous metal ion solution and then heating in a colourless Bunsen flame. Principle of flame test: The electrons of the ion absorb energy from the flame and get excited. Then this energy is emitted as visible light. Different ions have different electronic configurations, hence impart different colours to the flame. Characteristic flame colours of some metal ions Group Group 1 Group 1 Group 1 Group 2 Group 2 Transition metal Metal Lithium Sodium Potassium Calcium Barium Copper (Cu2+) Flame colour Red Yellow Lilac Orange-red Light-green Blue-green Test to identify the cations using aqueous sodium hydroxide: All metal cations form insoluble hydroxides when sodium hydroxide solution is added to them. The colour of the precipitate and its behaviour in excess sodium hydroxide will help identify the metal present. TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 17 of 21 Pursuit of Excellence Effect of adding NaOH to solution containing various metal ions Added dropwise White precipitate White precipitate Green precipitate Light blue precipitate Green precipitate Red-brown precipitate To excess Precipitate is soluble in excess, giving a colourless solution Precipitate is insoluble in excess Precipitate is insoluble in excess Precipitate is insoluble in excess Precipitate is insoluble in excess, turns brown near the surface on standing Precipitate is insoluble in excess Likely cation Al3+, Zn2+ Ca2+ Cr3+ Cu2+ Fe2+ Fe3+ **Note: 1. Ammonium cation forms a soluble hydroxide. However, on heating it forms ammonia gas and water. 2. The reaction with NaOH can be used to distinguish between Fe2+and Fe3+as the colour of precipitate is different. Test to identify the cations using dilute ammonia solution: Ammonia gas dissolved in water is called aqueous ammonia. The solution is weakly alkaline, which produces low hydroxide ions. The colour of the precipitate helps to identify the metal present. Effect of adding NaOH to solution containing various metal ions Added dropwise White precipitate No precipitate or very slight white precipitate Green precipitate Light blue precipitate Green precipitate Red-brown precipitate White precipitate To excess Precipitate is insoluble in excess No change Precipitate is insoluble in excess Precipitate is soluble in excess, giving a dark blue solution Precipitate is insoluble in excess, turns brown near the surface on standing Precipitate is insoluble in excess Precipitate is soluble in excess, giving a colourless solution Cation present Al3+ Ca2+ Cr3+ Cu2+ Fe2+ Fe3+ Zn2+ **Note: When aqueous ammonia is added to a solution of Cu2+ ions, the solution forms a gelatinous light blue precipitate. As more ammonia is added, the precipitate dissolves, forming a dark blue clear solution. TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 18 of 21 Pursuit of Excellence Test for gases: Various gases are produced during qualitative analysis. These gases can be identified using following tests Tests for gases Gas Colour Hydrogen (H2) Oxygen (O2) Colourless (odourless) Colourless (odourless) Effect of moist indicator paper No effect-neutral No effect-neutral Carbon dioxide (CO2) Ammonia (NH3) Sulphur dioxide (SO2) Colourless (odourless) Pink-weakly acidic Colourless (very pungent smell) Colourless (very choking smell) Blue-alkaline Chlorine (Cl2) Yellow-green (very choking smell) Water (H2O) Colourless (odourless) Bleaches moist indicator paper after it initially turns pale pink No effect-neutral Red-acidic TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Test Burns with a pop sound Relights the glowing splint Turns lime water cloudy white (milky) Turns damp red litmus blue Turns acidified potassium dichromate (VI) from orange to green Or Turns acidified potassium manganate (VII) from purple to colourless Bleaches damp litmus paper Turns blue cobalt chloride paper pink Or Turns anhydrous copper (II) sulphate from white to blue Page 19 of 21 Pursuit of Excellence Water Chemical Test for water: Presence of water can be detected using cobalt chloride or copper (II) sulphate. It turns blue cobalt chloride paper pink Or turns anhydrous copper (II) sulphate from white to blue Checking purity of water: Purity of water can be checked using melting point or boiling point technique. Water melts at 0oC and boils at 100oC. Impure sample will have varied melting point or boiling point, depending on the type of impurity. Melting and Boiling point: Melting point determination: https://www.youtube.com/watch?v=ggXHDZFsQBc Boiling point determination: https://www.youtube.com/watch?v=nZXoe0fgJ8Q Boiling point determination: The temperature at which a pure organic substance changes from the liquid phase to the gas phase is known as the boiling point. A liquid's boiling point can be determined using the capillary method, where an inverted capillary is placed in the liquid of interest and the liquid is heated. As the temperature increases, the air in the capillary escapes and is replaced by the vapor of the liquid. The vapor pressure in the capillary increases with temperature. Once it exceeds the atmospheric pressure, the vapor escapes the capillary in a stream of bubbles. When the heat is removed, the liquid cools, and the vapor pressure in the capillary decreases. When the vapor pressure reaches the atmospheric pressure, the liquid begins to fill the capillary. The temperature at which this occurs is the boiling point. Melting point: The temperature at which a solid melts and becomes a liquid is the melting point. Since this requires that the intermolecular forces that hold the solid together have to be overcome, the temperature at which melting occurs will depend on the structure of the molecule involved. Hence, different compounds tend to have different melting points. A pure substance has a sharp and characteristic melting point. Hence, the melting point of a compound is a criterion for purity as well as for identification. TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 20 of 21 Pursuit of Excellence The melting point of an organic solid can be determined by introducing a tiny amount into a small capillary tube, attaching this to the stem of a thermometer centred in a heating bath, heating the bath slowly, and observing the temperatures at which melting begins and is complete. Use of distilled water in practical chemistry: Distilled water is free of ions whereas the tap water is rich in ions. These ions of the tap water can give their own test or interfere with the results. So, distilled water is preferred. TSMS Noida /Chemistry/Practical Booklet/2023 - 25 Integrity Sensitivity Pride in One’s Own Heritage Page 21 of 21 Pursuit of Excellence
