Short Response Questions

1. What is a mole?

2. Differentiate between empirical formula and molecular formula.

3. What is the number of molecules in 9.0 g of steam?

4. What are the molar masses of uranium-238 and uranium-235?

5. Why do one mole of hydrogen molecules and one mole of H-atoms have different masses?

6. Define ion, molecular ion, formula unit, free radical, atomic number, mass number, atomic mass unit.

7. Describe how Avogadro's number is related to a mole of any substance.

8. Calculate the number of moles of each substance in samples with the following masses:

9. Calculate the mass in grams of each of the following samples:

10. Calculate the number of molecules present in each of the following samples:

11. Decide whether or not each of the following is an example of an empirical formula:

a) Al₂Cl₆

b) Hg₂Cl₂

c) NaCl

d) C₂H₆O

12. TNT or trinitrotoluene is an explosive compound used in bombs. It contains 7 C-atoms, 5 H-atoms, 3 N-atoms, and 6 O-atoms. Write its empirical formula.

13. A molecule contains four phosphorus atoms and ten oxygen atoms. Write the empirical formula of this compound. Also, determine the molar mass of this molecule.

14. Identify the substance that has a formula mass of 133.5 amu:

a) MgCl₂

b) BCl₃

c) AlCl₃

15. Calculate the number of atoms in each of the following samples:

a) 3.4 moles of nitrogen atoms

b) 23 g of Na

16. Calculate the mass of the following:

a) 3.24 × 10¹⁸ atoms of iron

b) 2 × 10¹⁰ molecules of nitrogen gas

c) 1 × 10²⁵ molecules of water

17. Balance the following chemical equations:

1. A balanced chemical equation shows the reaction between 2Mg + O₂ → 2MgO. How many moles of magnesium oxide (MgO) are produced from 0.5 moles of magnesium (Mg)?

2. Given the balanced equation 2H₂ + O₂ → 2H₂O, what is the coefficient in front of H₂O when 6 moles of hydrogen (H₂) react?

3. Explain the difference between a molecular formula and an empirical formula, and provide examples of each for a specific compound.

4. Describe a real-world application of stoichiometry.

5. Calculate the molar mass of H₂O and determine the number of moles in 18 grams of water.

6. If a reaction produces 5 moles of a product with a molar mass of 20 g/mol, calculate the mass of the product formed.

7. How is Avogadro's number used to relate the number of particles to the number of moles in a given sample? Provide an example for better understanding.

8. Calculate the molar mass of NaCl and determine the number of moles present in 58.5 grams of sodium chloride.

9. If the molar mass of a gas is 32 g/mol, determine the mass of 4 moles of this gas.

10. How does the periodic table help us predict the formula of an ionic compound?

11. What information is conveyed by the state symbols (s, l, g, aq) in a chemical equation?

12. What is the name given to the number of particles (atoms, molecules, ions) in one mole?

13. Explain the difference between a balanced and unbalanced chemical equation.

14. Aspirin (C₉H₈O₄) has a molar mass of 180.14 g/mol. How many moles of aspirin are present in 500 mg of aspirin (convert mg to g first)?