STOICHIOMETRY( Important Questions)

STOICHIOMETRY

Mole  and Avogadro Number:

1.      The atomic weight of Gold is 197.2 a.m.u. What is the weight of one Gold atom?How many gram atoms are in 7.58g of Au?

2.      A sample of chlorine gas at S.T.P. has a volume of 800cm³

calculate;

                        a)The number of moles chlorine

                        b)The mass of the sample

                        c) The number of chlorine molecules in the sample

3. How many atoms of carbon are present in 10g of coke

4. 10g of Na contain as many no. of atoms an in 10g of K

5. The atomic mass of Zn is 65.4 a.m.u.

a)The number of moles and also the number of atoms in 10.9g of Zn

b)The mass of 1.204 x 10²⁴  atoms of Zn

6.      The molecular weight of NaOH is 40; find

a)Its gram molecular weight.

b)Weight of 3 molecules in a.m.u.

c)Weight of 60200 molecules in gram

d) Weight of 6 Gram mole

7. Atomic mass of Na = 23 a.m.u.; Calculate

(i)                 Number of mole in 460g of Na

(ii)               Mass of 3.01* 10²³ atoms of Na

(iii)             Number of atoms in 4.6g of Na

8.      Calculate the number of moles and the number of molecules present in 9.0 gm of C₆H₁₂O₆

9.      Calculate the number of moles, the number of molecules and

the volume in cm³ of 0.32gm of    a ) CH₄      b) SO₂ gases at S.T.P.

            10.The atomic mass of sodium (Na) = 23 a.m.u.

                                    a) Calculate the mass of 2.408 x 10²³ atoms of Na

                        b) Calculate the number of moles of Na in 4.6gm.

11. What is the mass of 3.01 x 10²² molecules of N₂?

Empirical and Molecular Fromula:

1.      The empirical formula of a compound is CH₂O. If the molecular weight of the compound is 180; calculate the molecular formula

2.      Calculate the Empirical formula from the given percentage composition 68.8% carbon 5.0% Hydrogen 26.2% Oxygen

3.      A given compound contain C = 60%, H = 13%, O = 27%

Calculate its Empirical formula.

4.      1g of a sample of an organic substance was burnt in excess of oxygen yield 3.03g of CO₂ and 1.55g of H₂O. if the molecular mass of the compound is 58 a.m.u.; find the molecular formula.

5.      A given compound contain 75.2% carbon 10.75% hydrogen and 14.05% oxygen; calculate the empirical formula of the compound.

6.      Adipic acid used in the manufacture of Nylon the acid contain 49.3% carbon, 6.9% hydrogen and 43.8% oxygen by mass, the molecular mass 146 a.m.u. find the molecular formula of Adipic acid.

7.      A compound contain 40% carbon, 6.66% hydrogen by mass. Its

molecular mass if double that of its empirical mass. Find  Molecular formula.

8.      An organic compound contain 51.8% carbon, 13.12% hydrogen and 35.08% oxygen; determine the empirical formula of the compound

            (C = 12 a.m.u. , H = 1a.m.u., O = 16 a.m.u).

9.      A hydrocarbon ha 20%  hydrogen and 80% carbon: find the empirical and molecular formula o the compound if the molecular mass is 30.

10.   Diethyl zinc is a chemical used in the library to produce the books from the worms. Its composition is 53% zinc, 38.9% carbon and 8.1% hydrogen; find the empirical formula of the compound.

11.   An organic compound contains 67.7% of C and 7.41% of H, and 25.90% of N. the molecular mass of the compound is 108. Determine the empirical and molecular formulae of the compound.

12.   The molecular mass of a compound is 180 and its empirical formula is CH₂O: find the molecular formula.

Stoichiometry:

1. 30gm of lime stone (calcium carbonate CaCO₃) was heated,

                        a) Write the equation of the reaction

                        b) Calculate the mass of CO₂ produced

                        c) Calculate the volume of CO₂ at S.T.P.

2. 73.5gm of KClO₃ is decomposed on heating as follows:

            2KClO₃                   2KCl    +    3O₂

            Calculate:       a) The mass of KCl formed

                                    b) The volume of O₂ formed at S.T.P.

3.54 gram of Dinitrogen pentaoxide (N₂ O₅) is decomposed in

heating as

                        2N₂O₅                          4NO₂  +  O₂

                        Find the volume of NO₂ and O₂ produce at S.T.P.

4.      Calculate the volume of oxygen gas at N.T.P. required to burn 30g of CH₄ gas as shown in the following reaction.

CH₄   +   O₂                              CO₂  +  2H₂O

5.      Calculate the volume of nitrogen gas produce by heating 300g of ammonia gas at 21^oC and 823 torr pressure.

2NH₃                            N₂  +  3H₂

6.      Calculate the volume of the oxygen at S.T.P. that may be obtain by the decomposition of 51.3g of KClO₃ of heating in presence of catalyst.

2 KClO₃                      2KCl  +  3O₂

7.      Find the mass of KCIO₃, required to prepare 3.2 gm of O₂.

2 KCIO_3(s)                   2KCl_(s) + 3O_2(g)

Limiting reactant:

1.      You are provided with 6.0 gm of C and 100 gm of O₂

Calculate the amount of CO₂ prepared by reacting them. Which of them is the limiting reactant?

2.      At high temperature sulphur (S) combines with iron (Fe) to form brown black iron sulphide (FeS)

Fe    +    S                     FeS

In one experiment 76.2g of Fe are allowed to react 86.7g of sulphur; which of the two is limiting reactant; Calculate the amount of FeS obtained.

3.      Determine the mass of aluminum acetate that can be made if You do this reaction with 125 g of acetic acid and 275 g of aluminum hydroxide

3CH₃COOH  +Al(OH) ₃ → Al(CH₃COO) ₃ +3H₂O

What is the limiting reactant in the above problem ? How much of Excess reagent will be left over after the reaction is complete?

4 .Consider the following reaction:

                                    3CaCO₃ +2FePO₄→ Ca₃(PO₄) ₂  +Fe₂ (CO₃) ₃          

When 100 g of calcium carbonate anf 45 g of iron(III)Phosphate .    

What is the limiting reactant in the above problem ? How much of Excess reagent will be left over after the reaction is complete. What is the maximum amount of each products that can be formed?

Theoretical and Actual  Yield

1.      Calculate the theoretical yield of Calcium Oxide if 24.8 g of Calcium carbonate decomposes. Calculate the percent yield if we got 13.1 g in the laboratory .

   CaCO₃ →CaO + CO₂

2.       What is the percent yield  if we experimentally produce 1.65g of copper when 1.87g  of Aluminum  react with 9.65g of copper  (II)sulphate .

2Al +CuSO₄ →  Cu + Al₂(SO₄)₃

3.       Find the theoretical yield of silicon carbide if 50.0 g of silicon dioxide react with 79.1 g of Carbon .

SiO₂ + C      →   SiC +CO 

4.      What is the percent yield  if 155 g of calcium carbonate is treated with 250g of hydrochloric acid 142g of calcium chloride is obtained .

   CaCO₃  + HCl →CaCl₂ + CO₂ +H₂ O