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SS2: CHEMISTRY - 1ST TERM

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  1. Periodicity and Periodic Table I | Week 1
    5 Topics
    |
    1 Quiz
  2. Quantum Numbers Orbitals & Electrical Structure | Week 2
    6 Topics
    |
    1 Quiz
  3. Periodicity and Periodic Table II | Week 3
    12 Topics
    |
    1 Quiz
  4. Periodicity and Periodic Properties III | Week 4
    11 Topics
    |
    1 Quiz
  5. Periodicity and Periodic Properties IV | Week 5
    5 Topics
    |
    1 Quiz
  6. Mass-Volume Relationship in Reaction | Week 6
    8 Topics
    |
    1 Quiz
  7. Types of Reactions: Oxidation and Reduction | Week 7 & 8
    7 Topics
    |
    1 Quiz
  8. Oxidation – Reduction Reaction II | Week 9
    3 Topics
    |
    1 Quiz
  9. Electrode Potential and Electrochemical Cells I | Week 10
    6 Topics
    |
    1 Quiz
  10. Electrode Potential and Electrochemical Cells II | Week 11
    5 Topics
    |
    1 Quiz
  11. Electrolysis I | Week 12
    8 Topics
    |
    1 Quiz
  12. Electrolysis II | Week 13
    8 Topics
    |
    1 Quiz
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Topic Content:

  • Mass-Volume Calculations

In Mass-Volume Calculations a mass is given and a volume is to be found. This group of calculations depends upon the use of molar volume. The molar volume of any gas at standard temperature and pressure is 22.4 dm

Example 6.4.1:

Calculate the volume of Carbon[IV]oxide gas at STP when 5 g of zinc trioxocarbonate[V] is heated strongly.

[Zn = 65, C = 12, O = 16, molar volume = 22.4 dm3 at STP] 

Solution

ZnCO3[s]  → ZnO[s] + CO2[g]

1 mole of ZnCO3[s]  ⇒ 1 mole of CO2[g] at STP

1 × [65 + 12 + (16 × 3)] g of ZnCO3[s]  ⇒ 1 × 22.4 dm3 of CO2 at STP

125 g of ZnCO3[s]   ⇒ 22.4 dm3 of CO2 at STP

∴ 5 g of ZnCO3[s] ⇒ \( \frac{5}{125} \; \times \; \frac{22.4}{1}\) dm3 of CO2 at STP

= 0.896 dm3 of CO2[g] at STP

Example 6.4.2:

What volume of dry oxygen gas [measured at STP] will be produced from the decomposition of 2.45 g of potassium trioxochlorate [V] (KClO3)? 

[K = 39, Cl = 35.5, O = 16 molar volume = 22.4 dm3 at STP]

Solution

2KClO3[S] → 2KCl[s] + 302[g]

From the balanced equation;

2 moles of KClO ⇒ 3 moles of O2 at STP

2 × [39 + 35.5 + (16 × 3)] g of KClO ⇒ 3 × 22.4 dm3 of O2 at STP

∴ 245 g of KClO3[s]  ⇒ 67.2 dm3 of O2[g]

∴ 2.45 g of KClO3 ⇒ \( \frac{2.45}{245} \; \times \; \frac{67.2}{1}\)

= 0.67 dm3 of O2 at STP

Example 6.4.3:

Calculate the volume of Hydrogen gas measured at 30°C and 720 mmHg when 6.5 g of Zinc reacts with hydrochloric acid.

[Zn = 65, C = 12, H = 1, Cl = 35.5, molar volume = 22400 cm3 at STP]

Equation of reaction: 

Zn[s] + 2HCl[aq] → ZnCl2[aq] + H2[g]

1 mole of Zn[s] ⇒ 1 mole of H2[g] at STP

65 g of Zn[s]  ⇒ 22400 cm3 of H2[g] at STP

∴ 6.5 g of Zn[s] ⇒ \( \frac{6.5}{65} \; \times \; \frac{22400}{1} \) cm3 of H2[g] at STP                               

 = 2240 cm3 of H2[g] at STP

using: \( \frac{P_1 V_1}{T_1} =\frac{P_2 V_2}{T_2} \)

P1 = 760 mmHg                  P2 = 720 mmHg

V1 = 2240 cm3                    V2 = ?

T1 = 273 K                          T2 = 30°C + 273 = 303 K

V2 = \( \frac{P_1 V_1 T_2}{P_2 T_1} \)

V2 = \( \frac{760 \: \times \: 2240 \: \times \: 303}{720 \: \times \: 273} \\ \scriptsize = 2624.3 \: cm^3\)