Lab preparation XI

Laboratory preparation

1. Nepal APF School Kirtipur , Kathmandu Virtual Class Topic: Lab Preparation Class-XI By DP Paneru M.Sc Chemistry [email protected]

2. S.N. Content 1 Laboratory preparation Carbon Monoxide 2 Laboratory preparation of HI 3 Laboratory Preparation of hydrogen gas 4 Laboratory Preparation of hydrogen sulphide gas 5 Preparation of H 2 S by Kipp's Apparatus 6 Laboratory Preparation of SO 2 gas 7 Laboratory Preparation of Ethene 8 Laboratory Preparation of Ethyne

3. Lab Preparation of CO Carbon monoxide was first prepared in the laboratory in 1776 by J.M.F. de Lassone , a French chemist. As carbon monoxide is extremely poisonous, its preparation should be carried out only in a fume chamber. In the laboratory carbon monoxide is prepared oxalic acid crystals with conc. H 2 SO 4 . COOH                  ∆ │       + conc. H 2 SO 4    → CO 2  + CO + ( H 2 SO 4 .H 2 O) COOH                      

4. Conc. H 2 SO 4  dehydrates oxalic acid crystals and a mixture of CO 2  and CO is set free. The oxalic acid crystals are taken in a round bottomed flask and conc. H 2 SO 4  poured into it. On heating, mixture of gases (CO 2  and CO) is produced which is passed through sodium hydroxide where CO 2  is absorbed by it and CO is obtained. CO is collected in the gas jar by downward displacement of water. Physical Properties a)Carbon monoxide is colorless , almost odorless and tasteless gas . b) It is very slightly lighter than air. c)Carbon monoxide is only very slightly soluble in water. d) It is poisonous gas. Air containing even less than 1% of carbon monoxide, can be fatal, if breathed in for about 10 to 15 minutes.

5. Chemical properties It is neutral (neither acidic nor basic in nature). It doesn’t support combustion but burns with blue flame & gives carbon dioxide. 2CO + O 2 ⟶2CO 2 + Heat It reacts with hydrogen to form methanol (CH 3 -OH). CO + 2H 2 ⟶CH 3 −OH It reacts with chlorine to form phosgene (phosgene can be used as deadly weapon) CO + Cl 2 ⟶COCl 2 It reacts with caustic soda (NaOH) to form sodium formate ( HCOONa ). CO + NaOH⟶HCOONa It combines with metals like iron, nickel, cobalt to form carbonyls. Fe + 5CO⟶Fe(CO) 5 (Iron carbonyl) Ni + 4CO⟶Ni(CO) 4 (Nickel carbonyl) Co + 4CO⟶ Co(CO) 4 (Cobalt carbonyl) It reacts as the reductant . It reduces metals oxides into metal. Fe 2 O 3 + 3CO⟶2Fe + 3CO 2 (Ferric oxide to iron) ZnO + CO⟶Zn + CO 2 (Zinc oxide to zinc)

6. Uses Used as fuel. Used to prepare weapon ie . Phosgene. Purification of nickel by Mond’s process is done with it’s application .

7. Laboratory preparation of HI In the laboratory, HI is prepared by dropping water on a mixture of red phosphorus and iodine. A mixture of iodine and red phosphorus is taken in the flask and water is dropped from the funnel. HI with some vapour of iodine is evolved. P 4  + 6I 2  → 4PI 3 PI 3      +   3H 2 O   →   3HI   +    H 3 PO 3  ]  *  4 P 4  + 6I 2  + 12H 2 O → 12HI + 4H 3 PO 3 HI cannot be prepared in the same way as HCl by using conc. H 2 SO 4  because HI being stronger reducing agent, reduces the oxidizing acid ( i.e.conc . H 2 SO 4 ) to SO 2 . 2HI + H 2 SO 4  → SO 2  + 2H 2 O + I 2

8. Physical Properties Hydrogen iodide is a colorless gas, with an acrid odor . It is exceptionally soluble in water (245 g/100 mL), giving hydroiodic acid. The dissolution is exothermic. It is also slightly soluble in alcohols.

9. Laboratory Preparation of hydrogen gas Principle Hydrogen gas is prepared in laboratory by reacting dilute H 2 SO 4 . Zn + dil. H 2 SO 4 → ZnSO 4  + H 2 ↑ It is a redox reaction in which hydrogen is reduced and zinc is oxidized.

10. Procedure The apparatus is shown in the figure. To produce hydrogen, dilute H 2 SO 4  is poured from the dropping funnel into the Wolfe's bottle which consists of granulated zinc. The CuSO 4  crystals can be added as a positive catalyst. As H 2  gas is lighter than air it is collected by downward displacement of water. Precaution The zinc used must not be pure. Concentrated H 2 SO 4  should not be used instead of dilute H 2 SO 4  because of the oxidizing nature as conc. H 2 SO 4  reacts with zinc metal and gives SO 2  not H 2 Nitric acid cannot be used because with zinc it liberates nascent hydrogen and that reduces the acid into the oxides.

11. Physical Properties 1. It is colorless , orderless and tasteless. 2. It is insoluble in water. 3. It can be liquefied at high pressure and low temperature. 4. It is the lightest gas having very low density. 5. It is neutral to litmus. Chemical Properties The bond dissociation energy of hydrogen molecule is 436 KJ mol and atomic size is very small. Due to these reasons, it is less reactive in nature in nature. However, it reacts with metals, non-metals and other compounds under suitable conditions. 1. Hydrogen is a stable molecule. 2. Action with metals: With reactive metals like: Na, K, Ca etc. respective hydrides are formed. 2 Na +H 2 → 2NaH b) With less reactive metals:Finely divided metals like palladium (Pd), platinum (Pt), nickel (Ni), cobalt (Co) etc. absorb hydrogen to form interstitial hydrides.

12. 3. Action with non- metals:Hydrogen reacts with the number of non-metals under the specific condition. With oxygen:When hydrogen is heated with oxygen water is produced. 2H 2 + O 2 −−−→ 2H 2 O b)With halogens:Hydrogen reacts with halogens to produce hydrogen halides. Reactivity of hydrogen decreases from fluorine to iodine. dark H 2 + F 2 −−→ 2HF sunlight H 2 + Cl 2 −−−−−→2HCl 673K H 2 + Br 2 −−−→2HBr 713K/Pt H 2 + I 2 −−−−−→2HI

13. c) With nitrogen: When nitrogen is treated with hydrogen about 773K and in the presence of catalyst Fe & Mo as a promoter under a pressure of about 200 atmospheric pressure, ammonia gas is formed. The reaction is reversible and exothermic. N 2 + 3H 2 ⇌ 2NH 3 + Heat d) With sulphur: Sulphur when heated with hydrogen, produces hydrogen sulphide (H 2 S). 700K S 8 + 8H 2 −−−→8 H 2 S e) With carbon: Hydrogen reacts with carbon on heating to produce hydrocarbons. 1373K C + 2H 2 −−−→CH 4 1773K 2C + 3H 2 −−−→C 2 H 6

14. 4. With other compounds: With metal oxides: Hydrogen is a reducing agent. So, it reduces metal oxides into pure metals. Δ CuO + H 2 −→Cu + H 2 O Δ MgO + H 2 −→ Mg + H 2 O Δ F e 3 O 4 +4 H 2 −→ 3Fe + 4H 2 O b ) With carbon monoxide: Carbon monoxide reacts with hydrogen on heating about 537K and in the presence of catalyst ZnO and Cr O atmos. pressure to get methyl alcohol (methanol). 573K ZnO,Cr 2 O 3 (200 atom) CO + H 2 −−−−−−−−−−−−−−−−→CH 3 OH c) With unsaturated hydrocarbon: Unsaturated organic compounds like ethene (CH 2 = CH 2 ) reacts with hydrogen to produce saturated organic compounds like ethane. This reaction takes place in the presence of Ni, Pb or Pt powder on heating at about 473K. Ni or Pd or Pt CH 2 = CH 2 + H 2 −−−−−−−−−→ vegetable ghee (fat)

15. Hydrogen Sulphide (H 2 S) Hydrogen Sulphide is prepared by the action of dilute hydrochloric acid on iron(II) sulphide. FeS + HCl -----------------> FeCl 2  + H 2 S The liberated gas is collected above warm water (since it readily dissolves in cold water) or by downward delivery.

16. H 2 S cannot be prepared by treating FeS with HNO 3  because H 2 S once formed may reduce nitric acid to NO 2  and H 2 S is itself oxidized. 2HNO 3  + H 2 S→ 2H 2 O + 2NO 2  + S And conc. H 2 SO 4  cannot be used for the preparation ofhydrogen sulphide because conc. H 2 SO 4  behaves as an oxidizing agent and oxidizes hydrogen sulphide to sulphur . H 2 S + conc. H 2 SO 4  → 2H 2 O + 2SO 2  + S Physical Properties Hydrogen sulphide is colourless gas with rotten-gas smell; It turns litmus paper red, because of the acidic nature of the gas The gas is about 1.25 times denser than air, Purification of gas H 2 S gas is purified by passing heat through the suspension of MgO . MgO + 2H 2 S ⟶Mg(HS) 2 + H 2 O Mg(HS) 2 → H 2 S ↑ + MgS

17. Preparation of H 2 S by Kipp's Apparatus Principle Hydrogen sulphide gas is prepared in Kipp’s Apparatus by action of HCl on FeS . FeS + HCl -----------------> FeCl 2  + H 2 S For analytical purpose, H S gas is needed in small quantity in the regular interval in small quantity. For this purpose, Kipp'sapparatus is used. It contains bulbs 'A', 'B' and'C ' in which bulb 'A' has a long stem that connects bulb 'B' and 'C' as shown in the figure.

18. Working process The middle bulbs contain iron sulphide pieces. Dil H 2 SO 4 is poured from the top of bulb A. When acid just covers the FeS pieces after filling the bulb C reactions starts to give H 2 S gas and comes out when the tap is open. FeS + H 2 SO 4 ⟶FeSO 4 + H 2 S ↑ When the tap is closed, the gaseous pressure in bulb 'B' increases that pushes H 2 SO up, up to the bulb 'A' which breaks thecontact between acid and FeS and hence the formation of gas is stopped. When the tap is open H 2 S gas comes out and acids come in place of H 2 S and this process repeats .

19. Test of H 2 S It has a pungent smell(rotten egg odour) and is tested by passing it through the filter paper wetted by lead acetate which turns into black. Physical Properties 1. It is colourless gas with the pungent smell of rotten egg. 2. It is heavier than air. 3. It is fairly soluble in gas. 4. It is poisonous gas.

20. Laboratory Preparation of SO 2 gas Principle In the laboratory, SO 2 gas is prepared by the action of cupper turnings with concentrated sulphuric acid. Cu + 2H 2 SO 4 ⟶CuSO 4 + H 2 O + SO 2 Hence, formed gas is collected in the gas jar by upward displacement of air.

21. Procedure Cupper turnings pieces are taken in a round bottom flask. Conc. H 2 SO is poured through thistel funnel and apparatus is made air tight as shown in figure. After heating the flask, SO 2 gas is formed which can be dried by passing it through conc. H 2 SO 4 in order to absorb moisture, pure and dry gas is obtained in the gas jar by upward displacement of air. Physical Properties 1. It is a colour gas with a pungent suffocating odour. 2. It is 2.2 times heavier than air. 3. It is highly soluble in water and the solution is called sulphurous acid. 4. It can be easily liquefied to a colourless liquid at -10°C and solidified at -26°C.

22. Preparation of Ozone Ozone is best prepared by silent electric discharges through pure and dry oxygen. 3O 2 ⇌ 2O 3 − 96 cal Different types of ozonizers can be used for this purpose. The ozonizer contains an annular space between two tubes through which oxygen passes. In Siemen's ozoniser , the inner tube is of iron or glass and it's concentric with outer one of glass, partly coated with tin foil. Both these are connected to the two secondary terminals of an induction coil and the ozone produced is continuously swept out by the fresh current of oxygen.

23. Preparation of ethene In the laboratory ethene is prepared by dehydration of ethanol. On heating ethyl alcohol with sulphuric acid at a temperature of 170 °C temperature forms ethene .

24. Physical properties Ethene is a colourless gas. Ethene posses pleasant odour at STP. Ethene is completely soluble in organic solvents and slightly soluble in water. It is lighter than air. Boiling point of ethene is -102 ° C and melting point is: –169° C. It has anaesthetic effect on inhalation. Chemical properties Reactivity: Ethene is more reactive than ethane and methane , as it has a double bond. The double bond is weaker than single bond. Hence, it can be readily attacked any other reactant. The typical reactions of alkenes involve the breaking of the double bond to form two single bonds. Such reactions are called addition reactions. 2. Combustion Ethene on combustion produce carbon dioxide, water and heat. C 2 H 4 + 3O 2 → 2CO 2 + 2H 2 O + Heat

25. Addition of hydrogen to ethene : Gives ethane after catalytic hydrogenation in presence of nickel. Addition of chlorine: When treated with halogens, forms 1, 2, dihalo ethanes . Polymerisation: Polymerisation is a process in which large number of unsaturated hydrocarbons join together to form a big molecule. The big molecule formed in this process is called a polymer. The polymer polythene is formed by the polymerisation of ethene at high temperature and pressure.

26.   Test of Ethene Two common qualitative tests for unsaturation are the reaction of the compounds with bromide in carbon tetrachloride and with potassium permanganate.    1. Bromine in Carbon Tetrachloride    Bromine will add to the carbon-carbon double bond of alkenes to produce dibromoalkanes , characteristic dark red-brown color disappears at the end of reaction.Which indicate the presence of unsaturation .

27. Potassium Permanganate (Baeyer Test ) A second qualitative test for unsaturation , the Baeyer test, depends on the ability of potassium permanganate to oxidize the carbon-carbon double bond to give alkanediols only ethene gas gives both test and ethane doesn't give such tests .

28. Laboratory Preparation of Ethyne Ethyne is prepared by the action of water on calcium carbide. CaC 2  + 2H 2 O   → Ca(OH) 2  + C 2 H 2 A thin layer of sand is spread atomic the bottom of a conical flask. A few small pieces of calcium carbide (CaC 2 ) are placed over the sand. The whole apparatus is set upon. Water is added to the flask drop wise with the help of a thistle funnel. Ethyne (acetylene) gas so produced is collected in a gas jar by the downward displacement of water.