G11 C4 Stoichiometry Short Question answers

Chapter 4 Stoichiometry

Short Answer Questions

Questions & Answers

1. Do 49 g each of H₂SO₄ and H₃PO₄ have the same number of molecules but a different number of atoms?

Yes, because both are one-half mole. According to Avogadro's number, equal moles of any substance have the same number of molecules ($3.01 \times 10^{23}$ molecules in this case). However, the number of atoms is different because each molecule has a different number of atoms (H₂SO₄ has 7 atoms and H₃PO₄ has 8 atoms).

2. Do different gases with different masses occupy an equal volume at STP?

Yes, they do. According to **Avogadro's Law**, at Standard Temperature and Pressure (STP), one mole of any ideal gas occupies a volume of **22.4 dm³** (or liters). Since different gases can have the same number of moles (like one mole), they will occupy the same volume regardless of their molar mass.

3. Do one mole of Na and one mole of Al have an equal number of atoms but a different size of atoms?

Yes, they do. One mole of any element contains the same number of atoms, which is **Avogadro's number** ($6.022 \times 10^{23}$). However, the atomic size is determined by the number of electron shells and the effective nuclear charge. Sodium (Na) and Aluminum (Al) are in the same period but have different numbers of protons, resulting in different atomic radii.

4. Is the limiting reactant always in a lesser quantity in a reaction mixture?

Not necessarily. The **limiting reactant** is the reactant that is completely consumed first, which limits the amount of product that can be formed. Its identification depends on the **mole ratio** of the balanced chemical equation, not just the initial mass or volume. A reactant with a smaller initial mass could be in excess if its stoichiometric coefficient is also small.

5. Is the amount of product obtained through a balanced chemical equation greater than the amount obtained experimentally?

Yes, typically it is. The amount of product calculated from a balanced chemical equation is the **theoretical yield**, which assumes perfect conditions and 100% reaction completion. The **actual yield**, obtained from an experiment, is almost always less due to factors like incomplete reactions, side reactions, product loss during purification, and experimental errors. The relationship is expressed by the **percent yield** formula: (Actual Yield / Theoretical Yield) x 100%.

6. What are the basic assumptions in Stoichiometric calculations?

The basic assumptions for Stoichiometric calculations are:

• The reaction goes to **100% completion**.
• There are **no side reactions**.
• Reactants are completely converted to products based on the balanced chemical equation.
• The products are pure and fully recovered.

7. Why does 18g of steam have Avogadro's number of molecules while 58.5g of NaCl does not?

This statement is incorrect. Both **18g of steam** (H₂O) and **58.5g of NaCl** contain Avogadro's number of molecules/formula units. The molar mass of water ($H_2O$) is 18 g/mol, and the molar mass of sodium chloride ($NaCl$) is 58.5 g/mol. Since 18g of H₂O is one mole and 58.5g of NaCl is one mole, both contain **$6.022 \times 10^{23}$** particles (molecules for H₂O and formula units for NaCl).

8. Why do 2 moles of Na react with 1 mole of chlorine gas to produce 1 mole of NaCl?

This statement is also incorrect based on the **balanced chemical equation**. The correct balanced equation is: $2Na + Cl_2 \rightarrow 2NaCl$ This equation shows that **2 moles of Na** react with **1 mole of $Cl_2$** to produce **2 moles of NaCl**. The prompt's statement that it produces 1 mole of NaCl is wrong; it produces 2 moles of NaCl to satisfy the law of conservation of mass.

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