Chemistry Questions

Q1: Define Stoichiometry and explain its significance in Chemistry.

Q2: Define molecular formula of a compound as the number and types of different atoms in one molecule.

Q3: Define empirical formula of a compound as the simplest whole number ratio of different atoms in a molecule.

Q4: For many compounds, empirical and molecular formulas are the same. For example, water (H₂O), carbon dioxide (CO₂), ammonia (NH₃), sulphur dioxide (SO₂), etc. Can you show why?

Write the empirical formula for the compounds containing carbon to hydrogen in the following ratios:

(a) 1:4

(b) 2:6

(c) 2:2

(d) 6:6

Q5: Aspirin is used as a mild pain killer. There are nine carbon atoms, eight hydrogen atoms, and four oxygen atoms in this compound. Write its empirical and molecular formula.

Q6: Explain molecular mass and formula mass with examples.

1. Determine the molecular mass of glucose C₆H₁₂O₆, which is also known as blood sugar.

2. Determine the molecular mass of naphthalene C₁₀H₈, which is used in mothballs.

3. Sodium chloride, also called table salt, is used to flavor food, preserve meat, and in the preparation of a large number of compounds. Determine its formula mass.

4. Milk of magnesia, which contains Mg(OH)₂, is used to treat acidity. Determine its formula mass.

5. Potassium Chlorate (KClO₃) is commonly used for the laboratory preparation of oxygen gas. Calculate its formula mass.

6. When baking soda, NaHCO₃, is heated, carbon dioxide is released, which is responsible for the rising of cookies and bread. Determine the formula masses of baking soda and carbon dioxide.

7. The following compounds are used as fertilizers. Determine their formula masses:

(i) Urea, (NH₂)₂CO

(ii) Ammonium nitrate, NH₄NO₃

8. Write the molecular formula of glucose that has the empirical formula CH₂O, given that n = 6.

9. Write the formula for the following molecular compounds:

a. Sulphur trioxide

b. Phosphorus pentachloride

c. Phosphorus trichloride

d. Iodine pentafluoride

e. Carbon disulphide

Q7: Write the procedures for writing chemical formula and name of binary ionic compounds.

Q8: Discuss the concept of mole and Avogadro's number.

Q9: Write the difference between the terms gram atomic mass, gram molecular mass, and gram formula mass.

Calculate the molar masses of:

(a) Na

(b) Nitrogen

(c) Sucrose C₁₂H₂₂O₁₁

1. Calculate the mass of one mole of:

a) Copper

b) Iodine

c) Potassium

d) Oxygen

2. Differentiate between gram formula mass and gram molecular mass.

3. Aspirin is a compound that contains hydrogen and oxygen. It is used as a painkiller. An aspirin tablet contains 1.25 × 10²¹ molecules. How many moles of this compound are present in the tablet?

4. A method used to prevent rust in ships and underground pipelines involves connecting the iron to a block of a more active metal such as magnesium. This method is called cathodic protection. How many moles of magnesium are present in 1 billion (1 × 10⁹) atoms of magnesium?

5. Calculate the molar mass of sugar (C₁₂H₂₂O₁₁).

6. There are 3.01 × 10²⁵ molecules of CO present in a container. Calculate the number of moles and its mass.

7. What is molar mass and relative molecular mass?

8. Calculate the number of moles of magnesium oxide, MgO, in:

(a) 80g

(b) 10g of the compound. (Ar: O = 16, Mg = 24)

9. Calculate the number of moles of aluminum present in:

(a) 108g

(b) 13.5g of the element. (Ar: Al = 27)

10. Calculate the mass of 0.5 mol of bromine molecules. Bromine exists as molecules. Its formula is Br₂. The Ar of bromine is 80, so its Mr is 160.

11. How many molecules are present in 1.75 mol of carbon dioxide?

12. How many moles of carbon are present in 1.50 mol of aspirin, C₉H₈O₄?

13. Calculate the molar mass for lithium carbonate, Li₂CO₃.

14. A dentist orders 24.4 g of gold (Au) to prepare dental crowns and fillings. Calculate the number of moles of gold in the order.

15. Pencil lead contains graphite, which is the element carbon. Calculate the number of grams in 0.520 mol of carbon.

16. A salt shaker contains 73.7 g of NaCl. How many moles of NaCl are present?

17. How many atoms of sodium are present in 3 moles of sodium, and what is the mass of it?

18. How many atoms are in 1 amu and 1 g of hydrogen (H)?

19. How many atoms are present in 16g of O and 8g of S?

20. Is the mass of 1 mole of O and 1 mole of S the same?

Q10: What is a balanced chemical equation, and what are the steps and rules involved in balancing a chemical equation? Provide an example to illustrate the process.

Q11: Define and explain ionic equation.

Transform the following chemical equations into ionic equations:

Mg(s) + H₂SO₄(aq) → MgSO₄(aq) + H₂(g)

Mg(s) + 2H⁺(aq) + SO₄^2-(aq) → Mg²⁺(aq) + SO₄^2-(aq) + H₂(g)

Q12: Define molecular and structural formula.

Q13: How can you write the molecular formula of a compound from its structural formula?

Write the molecular formulae of the following compounds:

1. CH₃-CH₂-OH

2. CH₃-CH₂-NH₂

3. CH₃-CO-CH₃