Molar Mass Calculations - UNSOLVED PRACTICE SET

Q7. Define molar mass. How is molar mass related to molecular mass? Explain with an example.

Q8. Calculate the molar mass of the following compounds: (i) H₂O, (ii) CO₂, (iii) NaOH, (iv) CaCO₃.

Q9. Your mother buys 500 g of sugar (C₁₂H₂₂O₁₁) from the market. Calculate how many moles of sugar she has bought.

Q10. What is the relationship between the number of moles (n), mass (m), and molar mass (M)? Write the formula and use it to calculate the mass of 0.25 mole of calcium oxide (CaO).

Q11. Calculate the number of moles in: (i) 80 g of sodium hydroxide (NaOH), (ii) 73 g of hydrogen chloride (HCl), (iii) 170 g of ammonia (NH₃).

Q12. A student has 22 g of carbon dioxide (CO₂). Calculate: (i) the number of moles of CO₂, (ii) the number of molecules of CO₂, and (iii) the number of oxygen atoms in the sample.

Q13. Explain the concept of molar mass in detail. How does it differ from molecular mass? Derive the relationship between mass, number of moles, and molar mass. Calculate the molar mass of ammonium sulphate ((NH₄)₂SO₄) and determine how many moles are present in 66 g of the compound.

Q14. A chemistry teacher gives students a challenge problem: "I have a white crystalline compound. When I dissolve 15.8 g of it in water, I find that it contains 0.1 mole of the compound."

(a) Calculate the molar mass of the compound.

(b) If the compound contains potassium (K), manganese (Mn), and oxygen (O), and its formula is KMnO₄, verify whether your calculated molar mass matches the theoretical molar mass of KMnO₄.

(c) If the student uses 31.6 g of the same compound, how many moles will it contain?

(d) How many molecules will be present in 31.6 g of the compound?

Q15. "Molar mass calculations are the backbone of quantitative chemistry, used in everything from cooking to industrial manufacturing." Discuss this statement by explaining: (i) how molar mass helps in preparing solutions of known concentration, (ii) how it is used to calculate yield in chemical reactions, (iii) how it helps in determining the empirical and molecular formulae of unknown compounds, and (iv) its application in quality control in food and pharmaceutical industries.

Q16. A chemistry laboratory needs to prepare various solutions for experiments:

(a) How many grams of NaOH are needed to prepare 250 mL of a 2 M solution?

(b) How many grams of H₂SO₄ are needed to prepare 500 mL of a 0.5 M solution?

(c) If a student dissolves 5.85 g of NaCl in water to make 100 mL of solution, what is the molarity of the solution?

(d) A 0.1 M solution of glucose (C₆H₁₂O₆) is prepared. Calculate the mass of glucose in 200 mL of this solution.

Q17. An industrial chemist needs to produce 1000 kg of calcium oxide (CaO) by heating calcium carbonate (CaCO₃):

CaCO₃ → CaO + CO₂

(a) Calculate the molar mass of CaCO₃ and CaO.

(b) Calculate the number of moles of CaO in 1000 kg.

(c) According to the balanced equation, how many moles of CaCO₃ are required?

(d) Calculate the mass of CaCO₃ needed.

(e) If the industrial process is only 80% efficient, how much CaCO₃ should the chemist actually use?

Q18. A nutritionist is analyzing the protein content of different foods. Proteins contain nitrogen, and the amount of nitrogen can be used to estimate protein content using the conversion factor 6.25 (since proteins contain approximately 16% nitrogen by mass).

A sample of dal (lentils) contains 3.2 g of nitrogen per 100 g of dal.

(a) Calculate the mass of protein in 100 g of dal using the conversion factor.

(b) If a person needs 50 g of protein per day, how many grams of dal should they consume?

(c) The molecular formula of a common amino acid (building block of protein) is C₃H₇NO₂. Calculate its molar mass.

(d) Calculate the percentage of nitrogen in this amino acid.

(e) If this amino acid makes up 20% of the protein in dal, how many moles of this amino acid are present in the protein content of 100 g of dal?