Lab Manual. of Engineering Chemistry

Transcription

1 Lab Manual of Engineering Chemistry 1

2 1 Determination of Total Hardness of Water by Complexometric Titration with EDTA I Water Analysis 2 Determination of Chloride ion in a given Water sample by Argentometric Method (Mohr s Method) 3 Determination of Dissolved Oxygen present in a given Water sample by Iodometric Method (Winkler s Method) II Volumetric Analysis 4 5 Determination of Percentage of Available Chlorine present in Bleaching Powder sample Determination of amount of Iron and the number of Water molecules of Crystallization in Mohr s salt using Standard Potassium Dichromate solution III Analysis of Ores/Alloys 6 7 Determination of amount of Iron present in the given Iron Ore/Alloy by Permanganometry Determination of amount of Copper present in the given Copper Ore/Alloy by Iodometry IV Preparation of polymers 8 Preparation of Urea-Formaldehyde resin 9 Preparation of Phenol-Formaldehyde resin Internal Continuous Assessment (Maximum Marks 50 marks) 50% - Laboratory practical and record Max = 25 marks 10% - Regularity in the class Max = 5 marks 40% - Test Max = 20 marks [Time: 3 hours] Viva [Marks = 10] Contribution of Marks from Daily Lab Work = 30 marks Performance in Lab Record Attendance [Marks = 5] [Marks = 10] [Max = 5] Contribution of Marks from Internal Lab Exam = 20 marks [Time: 3 hours] Experiment [Marks = 10] Viva, Principle and Procedure 40 % for Tabulation 60 % for Accuracy [Marks = 10] [Marks = 4] [Marks = 6] Viva = 2 Prin = 4 Proc = 4 Std = 2 Est = 2 Std = 3 Est = 3 Total Marks = 30 Total Marks = 20 2

3 Expt. No: 1 Determination of Total Hardness of Water by Complexometric Titration [EDTA Method] Aim To determine the total hardness of a given water sample by complexometric titration (EDTA method) Theory Water which does not give ready and permanent lather with soap is called hard water. Presence of calcium and magnesium salts in the form of bicarbonate, chloride and sulphate in water makes water hard. Water free from soluble salts of calcium and magnesium is called soft water. It gives lather with soap easily. The property of water which restricts the lather formation with soap is called hardness. It is of two types: (a) temporary hardness and (b) permanent hardness Temporary Hardness: It is due to the presence of magnesium and calcium bicarbonates [Ca(HCO 3 ) 2 and Mg(HCO 3 ) 2 ]. Permanent Hardness: It is due to the presence of soluble salts of magnesium and calcium in the form of chlorides and sulphates in water (CaCl 2, CaSO 4, MgCl 2 and MgSO 4 ). The unit used for expressing the hardness of water is parts per million (ppm). It is the number of parts of calcium carbonate (CaCO 3 ) equivalent hardness present in one million parts of water. Eriochrome Black-T [EBT] is the indicator used in the determination of hardness by complexometric titration with EDTA. Here, Eriochrome Black-T is a complex organic compound [sodium-1-(1-hydroxy 2-naphthylato)-6-nitro-2-naphthol-4-sulphonate] and EDTA is a hexadentate ligand [disodium salt of ethylenediamine tetraacetic acid]. OH HO NaOOCH 2 C CH 2 COOH N N SO 3 Na N H 2 C H 2 C N Eriochrome Black-T [EBT] NO 2 HOOCH 2 C CH 2 COONa EDTA [Disodium salt of ethylenediamine tetraacetic acid] 3

4 Observations and Calculations (a) Standardisation of EDTA solution with standard hard water S.No Volume of standard hard water in ml Burette Readings in ml Initial Final Volume of EDTA solution in ml Concordant Volume of EDTA solution, V 1 = ml 1 ml of Standard hard water = 1 mg CaCO 3 V 1 ml of EDTA solution = 20 ml of Standard hard water 1 ml of EDTA solution, = (b) Estimation of Total Hardness of given water sample = 20 mg CaCO 3 =..mg CaCO 3 S.No Volume of given water sample in ml Burette Readings in ml Initial Final Volume of EDTA solution in ml Concordant Volume of EDTA solution, V 2 = ml 20 ml of given water sample = V 2 ml of EDTA solution = 1 ml of given water sample = 1000 ml of given water sample = Total Hardness of given water sample = = = =. 4

5 When Eriochrome Black-T is added to the hard water at ph around 10, it gives wine red coloured unstable complex with Ca 2+ and Mg 2+ ions of the sample water. Ca 2+ / Mg 2+ from hard water + EBT [Ca 2+ / Mg 2+ EBT] Wine red coloured unstable complex Now when this wine red-coloured solution is titrated against EDTA solution, EBT in the unstable complex is replaced by EDTA to form a stable metal-edta complex and liberates the free Eriochrome Black-T. At this point, the colour of the solution changes from wine red to original blue colour which showing the end point of the titration. Apparatus: Reagents: [Ca 2+ / Mg 2+ EBT] + EDTA [Ca 2+ / Mg 2+ EDTA] + free EBT Wine red coloured Stable metal-edta complex Blue colour unstable complex (Colourless) Conical flask, Burette, Pipette, Beaker, Measuring flask 0.1M EDTA solution, Eriochrome Black-T indicator, Basic buffer solution (NH 4 OH and NH 4 Cl), Standard hard water, Given water sample Procedure: (a) Standardisation of EDTA solution with standard hard water Pipette out 20 ml of standard hard water in a washed conical flask. Add 5ml basic buffer solution and 2-3 drops of Eriochrome Black-T indicator, the colour of the solution turns wine red. Titrate this solution against EDTA solution taken in the burette until the colour changes from wine red to clear blue at the end. The final reading of the burette is noted and the titration is repeated to get concordant value. (b) Estimation of Total Hardness of given water sample Pipette out 20 ml of given hard water in a washed conical flask. Add 5ml basic buffer solution and 2-3 drops of Eriochrome Black-T indicator, the colour of the solution turns wine red. Titrate this solution against EDTA solution taken in the burette until the colour changes from wine red to clear blue at the end. The final reading of the burette is noted and the titration is repeated to get concordant value. Result: The total hardness of given water sample is..ppm 5

6 Expt. No: 2 Determination of Chloride ion in a given Water sample by Argentometric Method (Mohr s Method) Aim To determine the chloride ion of a given water sample by Argentometric method (Mohr s method) Theory Chlorides are present in water usually as NaCl, MgCl 2 and CaCl 2. Although chlorides are not harmful as such, their concentrations over 250 ppm impart a peculiar taste to the water thus rendering the water unacceptable for drinking purposes. By argentometric method, chloride ions in a water sample (neutral or slightly alkaline) can be determined by titrating it against standard silver nitrate (AgNO 3 ) solution using potassium chromate (K 2 CrO 4 ) as an indicator. The ph should be in between 7-8. At higher ph, silver ions are precipitated as silver hydroxide. At lower ph, potassium chromate indicator is converted to potassium dichromate (K 2 Cr 2 O 7 ). Argentometric method is based on the precipitation titration in which silver nitrate solution is released from the burette to the water sample which contains chloride ions and indicator. The silver ions (from silver nitrate solution) react with chloride ions (from water sample) and chromate ions (from indicator) to form white precipitate of silver chloride and red precipitate of silver chromate. + + Red colour formed because of formation of silver chromate disappears initially as the solution contains high concentration of chloride ions. + + When the concentration of chloride ions has decreased, the red colour starts disappearing slowly and slowly on shaking and a stage is reached when all the chloride ions have formed silver chloride. One extra drop of silver nitrate at this point reacts with potassium chromate and reddish coloured silver chromate is formed

7 Observations and Calculations: Titration with the Blank solution S.No Volume of distilled water in ml Burette Readings in ml Initial Final Volume of AgNO 3 solution in ml Concordant Volume of AgNO 3 solution, V 1 = ml Titration with the Sample Water S.No Volume of given water sample in ml Burette Readings in ml Initial Final Volume of AgNO 3 solution in ml Concordant Volume of AgNO 3 solution, V 2 = ml Normality of standard AgNO 3 solution, N A = =, Volume of standard AgNO 3 solution, V A = = ml Volume of given water sample, V W = ml Normality of given water sample, N W can be calculated from the normality formula, i.e., N A x V A = N W x V W Normality of given water sample, N W = =..N Amount of chloride ions =. =. g/lit =..g/lit Amount of chloride ions in ppm =. mg/lit =..ppm 7

8 Apparatus: Reagents: Procedure: Conical flask, Burette, Measuring flask, Beakers Standard silver nitrate solution, Indicator potassium chromate solution Titration with the Blank solution Transfer 50 ml of the distilled water in a conical flask and add 3-4 drops of indicator potassium chromate solution. Slowly add standard silver nitrate solution from the burette and shake the solution well. At the end point, light yellow colour starts changing to red colour. The titration is repeated until a concordant volume V 1 is obtained. The blank correction for the indicator should be subtracted from the volume of the titrant obtained after titrating the sample solution as given below Titration with the Sample Water Transfer 50 ml of the given water sample in a conical flask and add 3-4 drops of indicator potassium chromate solution. Slowly add standard silver nitrate solution from the burette and shake the solution well. At the end point, light yellow colour starts changing to red colour and red colour persists. The titration is repeated until a concordant volume V 2 is obtained. Result: The amount of chloride ion in the given water sample is..ppm 8

9 Expt. No: 3 Determination of Dissolved Oxygen present in a given Water Sample by Iodometric Method (Winkler s Method) Aim To determine the amount of dissolved oxygen (D.O.) in a given water sample by Iodometric Method (Winkler s Method) Theory Oxygen is poorly soluble in water. The solubility of oxygen of air in fresh water varies from mg/lit. Dissolved oxygen is needed for living organism to maintain their biological process. It is an important factor in corrosion. Iodometric method (Winkler s method) is used for determining dissolved oxygen in water. The principle involved in the determination of dissolved oxygen is to bring about the oxidation of potassium iodide (KI) to iodine (I 2 ) with the dissolved oxygen present in the water sample after adding MnSO 4, KOH and KI, the basic manganic oxide formed act as an oxygen carrier to enable the dissolved oxygen in the molecular form to take part in the reaction Basic manganic oxide which on acidification gives The liberated iodine (I 2 ) is titrated against standard sodium thiosulphate (Na 2 S 2 O 3 ) solution using starch as indicator Apparatus: Conical flask, Burette, Measuring flask, Beakers Reagents: Procedure: Standard sodium thiosulphate solution, Potassium iodide solution, starch solution as indicator Take 100 ml of given water sample into a conical flask, and titrate slowly against N/50 standard sodium thiosulphate solution (taken in the burette). When the colour of the solution is very light yellowish add about 2 ml of freshly prepared starch solution, so the colour of the solution turned into blue. Continue the titration till the disappearance of blue colour of the solution and note down the volume of the titrant used. The titration is repeated until a concordant volume is obtained. Result: The amount of dissolved oxygen (D.O.) in a given water sample is..ppm 9

10 Observations and Calculations: S.No Volume of given water sample in ml Burette Readings in ml Initial Final Volume of Na 2 S 2 O 3 solution in ml Concordant Volume of Na 2 S 2 O 3 solution, V 1 = ml Normality of standard Na 2 S 2 O 3 solution, N 1 = =. Volume of standard Na 2 S 2 O 3 solution, V 1 = ml Volume of given water sample, V 2 =...ml Normality of given water sample, N 2 can be calculated from the normality formula, i.e., N 1 x V 1 = N 2 x V 2 Normality of given water sample, N 2 = =..N Amount of Dissolved Oxygen =. = g/lit = g/lit Amount of Dissolved Oxygen in ppm =.. mg/lit =..ppm 10

11 Expt. No: 4 Determination of the Percentage of Available Chlorine present in Bleaching Powder sample Aim Determine the percentage of available chlorine present in the given sample of bleaching powder. Theory Bleaching powder is used as a bleaching agent and also as a disinfectant. The main constituent of bleaching powder is calcium hypochlorite [Ca(OCl) 2 ] which supplies chlorine [Cl 2 ] with dilute acids So the available chlorine is defined as the percentage of chlorine made available by bleaching powder when treated with dilute acids. The available chlorine present in bleaching powder sample is determined iodometricaliy by treating its solution with an excess of potassium iodide solution in the acidic medium The liberated iodine (I 2 ) is treated with sodium thiosulphate (Na 2 S 2 O 3 ) solution using freshly prepared starch solution as indicator to be added near the end point. Apparatus: Reagents: Digital Balance, Burette, Conical flask, Measuring flask, Funnel, Glass rod, Beakers Bleaching powder, Standard sodium thiosulphate solution, 10% Potassium iodide (KI) solution, dilute acetic acid, freshly prepared starch solution as indicator 11

12 Observations and Calculations: S.No Volume of given bleaching powder solution in ml Burette Readings in ml Initial Final Volume of Na 2 S 2 O 3 solution in ml Concordant Volume of Na 2 S 2 O 3 solution, V 1 = ml Normality of standard Na 2 S 2 O 3 solution, N 1 = =. Volume of standard Na 2 S 2 O 3 solution, V 1 = ml Volume of given bleaching powder solution, V 2 =...ml Normality of given water sample, N 2 can be calculated from the normality formula, i.e., N 1 x V 1 = N 2 x V 2 Normality of given bleaching powder solution, N 2 = = N Amount of available chlorine =. =. g/lit =..g/lit Amount of available chlorine present in 100 ml of the solution =. =..g The percentage of available chlorine present in the given sample of bleaching powder (BP) = = =..% 12

13 Procedure:.g of bleaching powder is accurately weighed in a weighing bottle. It is transferred to a clean beaker and is ground to a thin paste with water. The mixture is allowed to settle and the milky supernatant liquid poured into a 100 ml standard flask. The residue in the beaker is ground with a little more water and the operation repeated until the whole of the sample has been quantitatively transferred into the standard flask. Then the solution is made up to the volume. The flask is shaken well for uniform concentration. 10 ml of the solution (use measuring flask) in a state of very fine suspension is taken into a conical flask and add 10 ml of distilled water into it. Then add 10 ml of 10% potassium iodide (KI) solution and 10 ml of dilute acetic acid. This solution [which contains liberated iodine (I 2 )] titrates with standard sodium thiosulphate solution (taken in the burette) until the dark brown colour changes to pale yellow. To this add, 2 ml of freshly prepared starch solution as indicator, so the colour of the solution turned into blue. Continue the titration till the disappearance of blue colour of the solution and note down the volume of the titrant used. The titration is repeated until a concordant volume is obtained. Result: The percentage of available chlorine present in the given sample of bleaching powder is..% 13

14 Expt. No: 5 Determination of Strength of Iron and the number of Water molecules of Crystallization in Mohr s salt using Standard Potassium Dichromate solution Aim To determine the strength of iron and the number of water molecules of crystallization in Mohr s salt provided standard potassium dichromate solution (N/20), using diphenyl amine as internal indicator. Theory Mohr s salt is ferrous ammonium sulphate [FeSO 4.(NH 4 ) 2 SO 4.6H 2 O]. For determination of the amount of iron in the given solution of Mohr s salt, a known volume of this solution is titrated with standard potassium dichromate solution (K 2 Cr 2 O 7 ) in a medium acidified with dilute sulphuric acid. Potassium dichromate oxidises ferrous sulphate (FeSO 4 ) present in Mohr s salt into ferric sulphate [Fe 2 (SO 4 ) 3 ] : For finding out the end point, internal indicator diphenyl amine is used. At the end point, all the ferrous ions present in the solution get completely oxidised to ferric ions by chromate ions and as soon as a slight excess of potassium dichromate solution is added. It leads to the oxidation of diphenyl amine which results in the formation of a blue coloured complex. This indicates the end point of the titration. N H Diphenyl amine Oxidation with K 2 Cr 2 O 7 Blue Coloured complex The number of water of water molecules of crystallization in Mohr s salt can be calculated from the following equation, = + 14

15 Observations and Calculations: S.No Volume of given solution of Mohr s salt in ml Burette Readings in ml Initial Final Volume of K 2 Cr 2 O 7 solution in ml Concordant Volume of K 2 Cr 2 O 7 solution, V 1 = ml Normality of standard K 2 Cr 2 O 7 solution, N 1 = =. Volume of standard K 2 Cr 2 O 7 solution, V 1 = ml Volume of given solution of Mohr s salt, V 2 =...ml Normality of given solution of Mohr s salt, N 2 can be calculated from the normality formula, i.e., N 1 x V 1 = N 2 x V 2 Normality of given solution of Mohr s salt, N 2 = =..N The strength of iron in the given sample of Mohr s salt =. =. g/lit = g/lit The strength of anhydrated Mohr s salt =. = g/lit =.. g/lit The strength of hydrated Mohr s salt = 20 g/lit Strength of hydrated salt 20 g/lit = Strength of anhydrated salt.g/lit = + The number of water molecules of crystallization in Mohr s salt, x =.. 15

16 Apparatus: Reagents: Burette, Conical flask, Pipette, Measuring flask Standard potassium dichromate solution, dilute sulphuric acid, 1:1 phosphoric acid, Indicator diphenyl amine Procedure: Pipette out 20 ml of given solution of Mohr s salt into a conical flask, add 5 ml of dilute sulphuric acid, 2-3 ml of 1:1 phosphoric acid and then two drops of diphenyl amine to this solution. Run the potassium dichromate solution in small lots from the burette, shaking the conical flask after each addition and also stirred at regular intervals. At the end point, the colourless solution becomes deep blue. Note down the volume of the titrant used. The titration is repeated until a concordant volume is obtained. Result: (i) The strength of iron in the given sample of Mohr s salt is.g/lit (ii) The number of water molecules of crystallization in Mohr s salt. 16

17 Expt. No: 6 Determination of the amount of Iron in the given Iron Ore/Alloy by Permanganometry Aim To determine the amount of iron present in the given iron ore/alloy using potassium permanganate (Permanganometry) provided standard Mohr s salt solution (N/20). Theory Minerals which are naturally occurring chemical substances in the earth s crust obtainable by mining. Out of many minerals in which a metal may be found, only a few are viable to be used as sources of that metal. Such minerals are known as Ores. Iron is the second most abundant metal in the earth s crust. The major ores of iron are Haematite (Fe 2 O 3 ), Magnetite (Fe 3 O 4 ), Siderite (FeCO 3 ) and Iron pyrites (FeS 2 ). Transition metals mix freely with each other in the molten state and on cooling a solid solution of different metals results in the form of alloys. The alloy formation is explained on the basis of similar sizes of atoms of these metals which allow the atoms of one metal to take up the position in the crystal lattice of the other. Steal is essentially an alloy of iron and carbon. Plain steel contains certain amount of C, Si, S, P and Mn apart from iron. For special purposes varying amounts of other metals such as Cr, V, Mo, W, Ti, Ni, Co, Zr and Cu are added. For determining the amount of iron in ore/alloy, the given ore/alloy sample is dissolved in dilute sulphuric acid, when the iron present as dissolved as ferrous sulphate (FeSO 4 ) and hydrogen gas is evolved. + + The amount of ferrous ion (Fe 2+ ) in the solution can be determined by a redox titration with standard potassium permanganate (KMnO 4 ) or potassium dichromate (K 2 Cr 2 O 7 ). The ionic equations of ferrous sulphate with acidified potassium permanganate are given below :

18 Observations and Calculations (a) Standardisation of KMnO 4 solution with standard Mohr s salt solution S.No Volume of standard Mohr s salt in ml, V 1 Burette Readings in ml Initial Final Volume of KMnO 4 solution in ml Concordant Volume of KMnO 4 solution, V 2 = ml Normality of standard Mohr s salt solution, N 1 = =. Volume of standard Mohr s salt solution, V 1 =.ml Volume of KMnO 4 solution, V 2 =.ml Normality of KMnO 4 solution, N 2 can be calculated from the normality formula, i.e., N 1 x V 1 = N 2 x V 2 Normality of KMnO 4 solution, N 2 = (b) Estimation of iron in the given iron ore/alloy = N S.No Volume of given solution of iron ore/alloy in ml Burette Readings in ml Initial Final Volume of KMnO 4 solution in ml Concordant Volume of KMnO 4 solution, V 2a = ml Normality of KMnO 4 solution, N 2 =..N Volume of KMnO 4 solution, V 2a =.ml Volume of given iron ore/alloy solution, V 3 =.ml Normality of given iron ore/alloy solution, N 3 can be calculated from the normality formula, i.e., N 2 x V 2a = N 3 x V 3 Normality of given iron ore/alloy solution, N 3 = = N Strength of iron in the given iron ore/alloy solution =. =. g/lit The amount of iron present in the given sample of iron ore/alloy is =.. / =.. / =.g 18

19 Apparatus: Reagents: Burette, Conical flask, Pipette, Measuring flask, Beakers Standard Mohr s salt solution, potassium permanganate solution, dilute sulphuric acid Procedure: (a) Standardisation of potassium permanganate solution Pipette out 20 ml of the N/20 standard Mohr s salt solution into a conical flask and add 10 ml of dilute sulphuric acid. Then, titrate this solution slowly against the potassium permanganate solution from the burette until a faint but permanent pink colour persists in the solution. Note down the volume of the titrant used. Repeat the titrations until a concordant volume is obtained. (b) Estimation of Iron in the given ore/alloy The whole of the given iron ore/alloy solution is transferred into the 100 ml standard flask. Make up the volume of the solution to 100 ml with distilled water and shake the solution thoroughly. Pipette out 20 ml of the solution into a conical flask, add 10 ml of dilute sulphuric acid and titrate against the potassium permanganate solution taken in the burette. The appearance of a faint but permanent pink colour marks the end point. Note down the volume of the titrant used. Repeat the titrations until a concordant volume is obtained. Result: The amount of iron present in the given sample of iron ore/alloy is..g 19

20 Expt. No: 7 Determination of the amount of Copper in the given Copper Ore/Alloy by Iodometry Aim To determine the amount of copper present in the given copper ore/alloy provided standard sodium thiosulphate solution (N/20). Theory The major ores of copper are Copper pyrites (CuFeS 2 ), Malachite [CuCO 3.Cu(OH) 2 ] and Cuprite (Cu 2 O). Brass is an alloy of copper and zinc. It may also contain small amounts of iron, lead, tin or aluminium. For determining the amount of copper in ore/alloy, the given ore/alloy sample is dissolved in nitric acid. The excess acid is neutralized by drop wise addition of Na 2 CO 3 solution until turbidity appears This turbidity is removed by drop wise addition of acetic acid solution The principle involved in the determination of amount of copper present in the given copper ore/alloy is to bring about the oxidation of potassium iodide (KI) to iodine (I 2 ) with copper ions (Cu 2+ ). + + The liberated iodine (I 2 ) is titrated against standard sodium thiosulphate (Na 2 S 2 O 3 ) solution using starch as indicator Starch+ I Blue coloured complex. + + Apparatus: Conical flask, Burette, Measuring flask, Beakers Reagents: Standard sodium thiosulphate solution, Potassium iodide solution, starch solution as indicator Procedure: The whole of the given copper ore/alloy solution is transferred into the 100 ml standard flask. Make up the volume of the solution to 100 ml with distilled water and shake the solution thoroughly. Pipette out 20 ml of the solution into a conical flask, neutralize any free acid present in this solution by adding sodium carbonate solution by drop wise till a faint permanent precipitate remains on shaking and add dilute acetic acid drop wise until the precipitate dissolves. Add 10 ml of potassium iodide (KI) solution, so the solution becomes brown and then titrate slowly against N/20 standard sodium thiosulphate solution. When the colour of the solution assumes faint yellow colour of iodine, add about 2 ml of freshly prepared starch solution, so the colour of the solution turned into blue. Continue the titration till the disappearance of blue colour of the solution and note down the volume of the titrant used. The titration is repeated until a concordant volume is obtained. Result: The amount of copper present in the given sample of copper ore/alloy is..g 20

21 Observations and Calculations: S.No Volume of given solution of copper ore/alloy in ml Burette Readings in ml Initial Final Volume of Na 2 S 2 O 3 solution in ml Concordant Volume of Na 2 S 2 O 3 solution, V 1 = ml Normality of standard Na 2 S 2 O 3 solution, N 1 = =. Volume of standard Na 2 S 2 O 3 solution, V 1 = ml Volume of given solution of copper ore/alloy, V 2 =...ml Normality of given solution of copper ore/alloy, N 2 can be calculated from the normality formula, i.e., N 1 x V 1 = N 2 x V 2 Normality of given solution of copper ore/alloy, N 2 = =..N Strength of copper in the given Cu ore/alloy solution =. =. g/lit = g/lit The amount of copper present in the given sample of copper ore/alloy is =.. / =.g 21

22 Expt. No: 8 Preparation of Urea-Formaldehyde Resin Aim To prepare urea-formaldehyde (UF) resin Theory Urea-formaldehyde resin is prepared by the condensation polymerisation reaction between urea and formaldehyde in neutral or acidic condition. Such resins are water soluble and hence are used as textile finishing. They are also used in the paper industry to improve the wet strength of paper. In the plywood industry they are used as adhesives. Such resins find uses in packaging, accessories, unbreakable dishes, clock cases, etc. NH 2 H NHCH 2 OH NHCH 2 OH O C + O C O C + O C NH 2 H NH 2 NHCH 2 OH Urea Formaldehyde Monomethylol urea Dimethylol urea NHCH 2 OH NCH 2 n O C O C NH 2 Monomethylol urea NH 2 Linear UF resins n NHCH 2 OH NCH 2 n O C O C NHCH 2 OH NCH 2 n Dimethylol urea Cross linked UF resins 22

23 Apparatus: Beaker, Glass rod, Measuring flask, Funnel, Filter paper Reagents: Urea, 40% formaldehyde solution, Concentrated Sulphuric acid Procedure: Place 10 ml of 40% formaldehyde solution in a beaker. Add about 5g of urea while stirring until a saturated solution is obtained. Add a few drops of concentrated sulphuric acid stirring cautiously during the addition. All of a sudden a voluminous while solid mass appears in the beaker. When the reaction is complete, wash the residue with water and dry the product and determine the yield of the product. Result: The yield of the urea-formaldehyde (UF) resin is g 23

24 Expt. No: 9 Preparation of Phenol-Formaldehyde Resin Aim To prepare phenol-formaldehyde (PF) resin Theory Phenol - formaldehyde polymers (also called Bakelite) are the oldest synthetic polymers. These are obtained by the condensation reaction of phenol with formaldehyde in the presence of either an acid or a base catalyst. In the presence of acid catalyst, the reaction starts with the initial formation of o-and/or p-hydroxymethylphenol derivatives, which further react with phenol to form compounds having rings joined to each other through CH 2 groups. The initial product could be a linear product Novolac used in paints. Novolac on heating with formaldehyde undergoes cross linking to form infusible solid mass called Bakelite. It is used for making combs, phonograph records, electrical switches and handles of various utensils. 24

25 Apparatus: Beaker, Glass rod, Measuring flask, Funnel, Filter paper Reagents: Phenol, 40% Formaldehyde solution, Glacial acetic acid, Concentrated hydrochloric acid Procedure: Place 5 ml of glacial acetic acid and 2 ml of 40% formaldehyde solution in a beaker and add about 2g of phenol. Wrap a cloth or towel loosely round the beaker. Add a few ml of concentrated hydrochloric acid into the mixture carefully and heat it slightly. Within five minutes, a large mass of pink plastic is formed. The residue obtained is washed with water, filtered, then dry the product and determine the yield of the product. Result: The yield of the phenol-formaldehyde (PF) resin is g 25