EUDIOMETRY (GAS ANALYSIS) :- APPLICATION OF POAC ON EUDIOMETRY (gas analysis) NUMERICALS and HOW TO FIND OUT MOLECULAR FORMULAOF ANY HYDROCARBON USING "POAC" Eudiometry:- Eudiometry means gas analysis. It means in this type of numericals either you have to find out vol. of GAS From the data given in question or you have to find out any other thing like molecular formula of hydrocarbon ,no. of mole , mass of any other reactant and vol. of GAS is given. Specific gases are absorbed in specific reagents as given below Reactants KOH solution Alkaline Pyrogallol Absorbed gases CO2 & SO2 O2 Solution of ammonical cuprous chloride CO And if the mixture is cooled, H2O vapour changes to liquid. Hence, when temperature is above 100 0C (373 K) then only volume of H2O is considered. Eudiometry is mainly based on Avogadro's law, A (g) + B (g) → C(g) + D(g) a volume b volume c volume d volume a moles b moles c moles d moles Q.1 Three moles of Na2CO3 is reacted with 6 moles of HCl solution. Find out the volume of CO2 gas produced at STP Sol. Na2CO3→ NaCl + CO2 Apply POAC on C atom 2 litre HOW TO FIND OUT MOLECULAR FORMULA OF ANY HYDROCARBON USING POAC:Q. This vol. of ( CO2 + unreacted O2) = 70 ml. at NTP. of CO2 = 3 * 22.Cx Hy + O2 → CO2+ H2O Vol. What is the formula of hydrocarbon? Solution: . Vol. of moles of CO2 So no. of moles of C atoms in Na2CO3 = no. became 50 ml on treatment with KOH solution. of CO2 in the mixture was 20 ml. of O2 at NTP. of mole of Cx Hy = 1* no. of mole of CO2 -----------------------( i ) .4 litre = 67. mix. Vol. 10 ml.No. Apply POAC on C atoms X* no. of CO2 = 20 ml. of hydrocarbon = 10 ml. Because CO2 can be absorbed by KOH . of O2 reacted = 80 -50 = 30 ml. Is treated it becames 50 ml it means vol. of moles of C atoms in CO2 1* no. of moles of CO2 = 3 moles (given) Vol. which is absorbed by KOH and remaining 50 ml. of a gaseous hydrocarbon was burnt completely in 80 ml. of moles of Na2CO3 = 1* no. of moles of Na2CO3 = no. So when this 70 ml. was unreacted O2 ( O2 can NOT absorbed by KOH) So vol. The remaining gas occupied 70 ml. = 2* vapour density . Determine its molecular formula. of mole of H2O+2* no. of mole of H2O -----------------( ii ) Apply POAC on O atoms 2* no. of mole of CO2 2*30 = Y/2*10 + 2 *20 20 = 10Y/2 Y=4 Put the value of X and Y in Cx Hy The molecular formula of hydrocarbon is C2H4 TRY TO SOLVE FOLLOWING QUESTION Q. of mole of Cx Hy + 2* no.2 7.molecular wt.X* 10 = 20 So X = 20/10= 2 Apply POAC on H atoms Y* no. of moles of Cx Hy = 2* no. of moles of O2 = y/2* no. of mole of CO2 From eq. Solution ( HINT ) :.5 ml of hydrocarbon gas was exploded with excess of oxygen. (ii) 2* no. if vapour density of hydrocarbon is 14. of moles of O2 = 1* no. On cooling it was found to have undergone a contraction of 15 ml. C2H4 Q.5 ml.3 7. of which was absorbed by KOH and the rest was absorbed in a solution of alkaline pyrogallol. Answer:. The vol.C2H4 . are measured under the same conditions. If all vol. 15 ml. of gases on cooling was found to be 28. determine the molecular formula of hydrocarbon.5 ml of hydrocarbon gas was exploded with 36 ml..Answer:.of oxygen.