## Stoichiometry Long Questions

This page consists of long questions on stoichiometry included in the First Year course for all BISE Khyber Pakhtunkhwa.

Question 3: (a) What is formula mass of a compound? What are the steps involved in calculating the formula mass of a compound? Explain with an example.

(b) Calculate formula mass of the following compounds. (i) HNO3, (ii) C6H12O6, (iii) C3H8 (iv) C2H5OH (v) Al2O3, (vi) K2Cr2O7

Question 4: (a) Define and explain mole and Avogadro number with example.

(b) Given the equation CH4 (g) + 2O2 (g) ——→ CO2 (g) + 2H2O (g) + Heat, how can this be read in terms of particles, moles and masses?

Question 5: (a) What do you mean by percentage composition of a compound? How the percentage of an element is calculated in a compound?

(b) Calculate the percentage composition of each of the following compounds. (Given atomic weights of the elements).

(i) MgSO4 (ii) C3H6O (iii) KMnO4 (iv) C6H6 (v) NaAl(SO4)2 (vi) CaCO3 (vii) CH4

[Mg = 24, S = 32, O = 16, C = 12, K = 39, Na = 23, Mn = 55, Ca = 40, Al = 27, H = 1]

Question 6: (a) Differentiate between a “limiting reagent” and a “reagent in excess”. How will you identify the limiting reagent in a chemical reaction?

(b) How does a limiting reagent control the amount of the product formed? Give an example.

Question 7: A technician weighs 40 g of sodium. How many moles of formula units are in the sample?

Question 8: Calculate the mass in grams of (a) 7.75 moles of Al2O3 (b) 15 moles of H2SO4 (c) 1.0 × 1025 molecules of H2O.

Question 9: How many moles are present in each of the following samples?

(a) 30 g of MgS, (b) 75 g of Ca, (c) 8.85 kg of CO2 (d) 40 dm3 of O2 gas at STP, (e) 7.5 × 1020 molecules of C6H6.

Question 10: Calculate the mass percentage of a metal in a compound that is formed by0.233 g of metal combining with 0.354 g of oxygen.

Question 11: Given the equation:             2H2 (g) + O2 (g) ——→ 2H2O (g)

(a) How many moles of water will be obtained by burning 5.6 moles of O2 in an excess of H2?

(b) How many moles of O2 would be needed to react 58.5 g of H2 to form water?

(c) How many grams of H2 would be needed to form 120 g of H2O?

Question 12: Given the equation N2 (g) + 3H2 (g) ——→ 2NH3 (g) at STP. How many moles of NH3 would be formed if 6.3 dm3 of N2 gas react with an excess of H2?

Question 13: Calculate the mass of Mg metal require to consume 2560 g of CO2 in the reaction                   2Mg(s) + CO2(s) ——→ 2MgO(S) + C(s)

Question 14: When steam is passed through red hot carbon, a mixture of H2 and CO gas called water gas is formed.

H2 O (g) + C(S)  ——→ CO (g) + H2 (g)

(a) Which is the limiting reagent if 24.5 g of carbon is mixed with 1.89 moles of water vapors?

(b) Calculate the amount in grams of the excess reagent left unreacted.

Question 15: Calculate the percentage yield if 6.53 g of hydrogen gas is produced when 5 moles of Zn is consumed in the reaction.

Zn(s) + 2HCl (aq) ——→ ZnCl2 (aq) + H2 (g)

Question 16: The percentage yield of the following reaction is 85%.

2Al(s) + 3Cl2(g) ——→ 2AlCl3(s)

How many grams of AlCl3 will be actually obtained from 100 g of aluminum metal?