Mole Concept empirical & molecular formula by S.K.sinha See Chemistry Animations at sinhalab.com

SINHA I.I.T. CHEMISTRY

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MOLE CONCEPT(E.F & M.W.) Q.5

(i) Butyric acid contains only C, H and O. A 4.24 mg sample of butyric acid is completely burned. It gives 8.45 mg of carbon dioxide and 3.46 mg of water. What is the mass percentage of each elements in butyric acid? (ii) If the elemental composition of butyric acid is found to be 54.2 & C, 9.2% H and 36.6 % O, determine the empirical formula. (iii) The molecular mass of butyric acid was determined by experiment to be 88. What is the molecular formula?

Q.6

Fe2(SO4)3 is empirical formula of crystalline compound of iron. It is used in water and sewage treatment to aid in the removal of suspended impurities. Calculate the mass percentage of iron sulphur and oxygen in this compound.

Q.7

A 40 ml mixture of methane and ethylene when exploded with certain volume of oxygen which is just sufficient for combustion, produced 60 ml of CO2 gas. Calculate the ratio between the volumes of CH4 and C2H4 in the mixture. What volume of oxygen is required, if the ratio between the volumes of C2H4 and CH4 is first reversed and then doubled? What volume of CO2 is produced? Assume, all the volumes being measured under identical conditions.

Q.9

5.325 g sample of methyl benzoate a compound used in the manufacture of perfumes is found to contain 3.758 g of carbon, 0.316 g hydrogen and 1.251 g of oxygen. What is empirical formula of compound. If mol. weight of methyl benzoate is 136.0, calculate its molecular formula.

Q.12

Potassium bromide KBr contains 32.9 % by mass potassium. If 6.40 g of bromine reacts with 3.60 g of potassium, calculate the number of moles of potassium which combine with bromine to form KBr.

Q.16

How many moles of potassium chlorate to be heated to produce 5.6 lt. oxygen at STP?

Q.17

Weight of 1 liter milk is 1.032 kg. It contains butter fat (density 865 kgm-3) to the extent of4.0% by volume. Calculate the density of the fat-free skimmed milk.

Q.18

For the reaction:

Q.24

Chlorophyll the green coloring matter of plants responsible for photosynthesis, contains 2.68% of magnesium by mass. Calculate the number of magnesium atoms in 2.00 g of chlorophyll.

Q.25

How much CaCl2.6H2O and water must be weighed to prepare 100 g of a solution that is 5.0% CaCl2.

Q.26

Calculate the percentage composition in terms of mass of a solution obtained by mixing 300 g of a 25% and 400 g of a 40% solution by mass.

Q.27

2Na3PO4 + 3 Ba(NO3)2 Ba3(PO4)2 + 6 NaOH Suppose that a solution containing 32.8 g of Na3PO4 and 26.1 g of Ba(NO3)2 is mixed. How many g of Ba3(PO4)2 are formed?

When dissolved in dilute H2SO4, 0.275 g of metal evolved 119.7 ml of H2 at 20C and 780.4mm pressure. H2 was collected over water. Aqueous tension is 17.4 mm at 20C. Calculate equivalent weight of metal.

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SINHA I.I.T. CHEMISTRY

Q.28

A gaseous alkane on complete combustion gives CO2 and H2O. If the ratio of moles of O2 needed for combustion and moles of CO2 formed is 5:3 find out the formula of alkane.

Q.29

A 5.0 g quantity of white phosphorous was burned in an excess of oxygen and the product was dissolved in water to make 250 ml solution. (a) Write balanced equations for the reaction. (b) When the solution was treated with an excess of aqueous Ca(NO3)2 a while precipitate was obtained . What was it and how much it formed. (c) The precipitate in part (b) was removed and the solution was treated with an excess of Zn yielding a colorless gas collected at 20C and 742 mm of Hg. What was the gas and how much volume of it was formed?

Q.30

Find the milli-equivalents (a) Ca(OH)2 in 111 g (b) NaOH in 30 g

(c) H2SO4 in 4.9 g

Q.40

What is the strength in g per liter of a solution of H2SO4, 12 ml of which neutralized 15 ml of N/10 NaOH solution.

Q.41

Calculate the concentration of a solution obtained by mixing 300g 25% by weight solution of NH4Cl and 150 g of 40% by weight solution of NH4Cl.

Q.42

A sample of NaOH weighing 0.38 g is dissolved in water and the solution is made to 50 ml in a volumetric flask. What is the molarity of the resulting solution.

Q.44

How many moles of NaOH are contained in 27 ml of 0.15 M NaOH?

Q.45

A sample of NaNO3 weighing 0.38 is placed in a 50 ml volumetric flask. The flask is then filled with water to the mark on the neck. What is the molarity of the solution.

Q.46

In a reaction vessel 0.184 g of NaOH is required to be added for completing the reaction. How many milliliter of 0.15 M NaOH solution should be added for this requirement.

Q.47

Commercially available concentrated hydrochloric acid contains 38% HCl by mass. (a) What is the molarity of this solution? The density is 1.19 g ml-1. (b) What volume of concentrated HCl is required to make 1.00 liter of 0.10 M HCl?

Q.48

Concentrated nitric acid used in the laboratory work is 68% nitric acid by mass in aqueous solution. What should be the molarity of such a sample of the acid if the density of solution is 1.504 g ml-1

Q.49

A solution of glucose in water is labeled as 10 percent w/w, what would be the molarity and mole fraction of each component in the solution? If the density of the solution is 1.2 g ml-1, then what shall be the molarity of the solution?

Q.50

The acidic substance in vinegar in acetic acid. When 6.0 g of a certain vinegar was titrated with 0.1 M NaOH. 40.11 ml of base had to be added to reach the equivalence point. What percent by mass of this sample of vinegar is acetic acid?

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SINHA I.I.T. CHEMISTRY

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ANSWERS Q.1

Q.2. 1.54 CO2 , 3.5 X 10-2 mole

P= 26, Q= 18

Q.3. 50%

Q.4 mass of CO formed = 823.48 g Q.5. (i) C = 54.35% ,H = 9.06% O = 36.59% (ii) empirical formula =C2H4O (iii) Molecular formula = C4H8 O2 Q.6. % of Fe = 28% , % of S = 24 % , % of O = 48% Q.8. Molecular formula = CH Q.10. 6.43 kJ

Q.7. CO2 = 66.64 ml, O2 = 106.67 ml

Q.9. Empirical formula = C4H4O ,Molecular formula = C8H8O2

Q.11. 3.14 mole H2O

Q.12. moles of K = 8.01 X 10-2 mole

Q.13. Moles of H2 formed = 0.26 Q.14. (a) Thus limiting reagent = Al (b) Moles of AlCl3 formed = 1.0 (c) Moles of excess reagent Cl2 left unreacted = 1.5 Q.15. Volume of H2 at STP = 11200 ml Q.17. density of fat free skimmed milk = 1038.5 kh/m3

Q.16. 1/6 mole KClO3 Q.18. 20.07 g Fe3O4 = 78.94%

Q.19. CaO = 151.20 kg Q.20. Fe2O3 Q.21. FeO= 21.06% , Q.22. Al= 1.25 g , Zn = 0.42 g Q.23. 8.39 g HCl

Q.24. 1.345 X 1021 atoms of Mg. Q.26. 33.57%

Q.25. 9.9 g CaCl2.6H2O, mass of water = 90.1 g

Q.27. E = 27.52

Q.28. alkane = C3H8

Q.29. (a) 0.16 (b) Moles of HNO3 = 0.48 (c) Moles of N2O = 1.18 lt. Q.30. (a) = 3000 (b) = 750 (c) = 100 Q.31. w = 2.4 g Q.32. N = 0.0166 Q.33. w = 23.52 g Q.34. (a) 0.0167 (b) 0.267 (c) 0.1 (d) 9.9 Q.37. V = 857.14 ml Q.41. 30%

Q.35. 40 ml

Q.38. 0.5978g Q.42. N = 0.19

Q.45. Molarity = 8.94 X 10-2

Q.36.V = 1.44 ml

Q.39. Molarity = 0.07 Q.43. 1.05 M

Q.46. V = 30.67 ml

Q.40. 6.125 g lt-1

Q.44. 4.05 X 10-3 Q.47.V= 8.06 ml

Q.48. 16.23 M Q.49. Molality = 0.647 m , Molarity = 0.67 M Mole fraction of glucose = 0.011 Mole fraction of water = 0.989 Q.50. 4.01

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