Question

Lead can be prepared from galena [lead(II) sulfide] by first roasting the galena in oxygen gas to form lead(II) oxide and sulfur dioxide. Heating the metal oxide with more galena forms the molten metal and more sulfur dioxide. (a) Write a balanced equation for each step. (b) Write an overall balanced equation for the process. (c) How many metric tons of sulfur dioxide form for every metric ton of lead obtained?

Short answer

The balanced equations are: \[ 2PbS + 3O_2 \rightarrow 2PbO + 2SO_2 \] \[ 2PbO + PbS \rightarrow 3Pb + SO_2 \] Overall: \[ PbS + O_2 \rightarrow Pb + SO_2 \] 1 metric ton of lead produces 1 metric ton of sulfur dioxide.

Step-by-step solution

Identify the Chemical Reactions

The preparation of lead from galena involves two key reactions. First, galena (lead(II) sulfide) is roasted in oxygen to form lead(II) oxide and sulfur dioxide. Second, lead(II) oxide reacts with more galena to produce molten lead and sulfur dioxide.

Write the Balanced Equation for Roasting Galena

The first reaction is the roasting of galena: Typically: \[ 2PbS + 3O_2 \rightarrow 2PbO + 2SO_2 \] This equation shows lead(II) sulfide reacting with oxygen gas to produce lead(II) oxide and sulfur dioxide.

Write the Balanced Equation for the Reaction with Lead(II) Oxide

The second reaction involves lead(II) oxide reacting with more galena: \[ 2PbO + PbS \rightarrow 3Pb + SO_2 \] This equation shows lead(II) oxide reacting with lead(II) sulfide to produce molten lead and sulfur dioxide.

Write the Overall Balanced Equation

Combine the two equations from Steps 1 and 2 to get the overall balanced equation for the process. By adding them together: \[ (2PbS + 3O_2 \rightarrow 2PbO + 2SO_2) + (2PbO + PbS \rightarrow 3Pb + SO_2) \] Result: \[ 3PbS + 3O_2 \rightarrow 3Pb + 3SO_2 \] Further reduced: \[ PbS + O_2 \rightarrow Pb + SO_2 \]

Calculate the Sulfur Dioxide Produced

To find the amount of sulfur dioxide produced, use the stoichiometric coefficients from the balanced overall equation: Each mole of PbS produces one mole of SO_2. Given that we are forming 1 metric ton (Mg) of Pb, the same amount, 1 metric ton, of SO_2 is produced.

Key concepts

chemical reactions

Chemical reactions are transformations where one or more substances change into new substances. In the process of extracting lead from galena, two main chemical reactions occur.
First, galena (lead(II) sulfide) reacts with oxygen to produce lead(II) oxide and sulfur dioxide. Then, lead(II) oxide reacts with more galena to yield molten lead and additional sulfur dioxide.
These reactions are critical. They enable us to obtain pure lead from its ore, highlighting the power of chemical transformations.

stoichiometry

Stoichiometry is the part of chemistry that studies relationships between quantities of reactants and products in a chemical reaction. It helps us understand how much of each substance is needed or produced.
In our lead extraction example, stoichiometry tells us the precise amounts of galena (PbS) and oxygen needed, and the quantities of lead and sulfur dioxide produced.

• For every mole of PbS, one mole of Pb and one mole of SO2 are produced
• This is essential for calculating materials needed and products formed

balanced equations

Balanced equations are crucial in chemistry. They show that mass is conserved in a chemical reaction—atoms are neither created nor destroyed.
For extracting lead from galena, we write and balance the equations accordingly:

• The roasting of galena: \( 2PbS + 3O_2 \rightarrow 2PbO + 2SO_2 \)
• Lead(II) oxide reacting with galena: \( 2PbO + PbS \rightarrow 3Pb + SO_2 \)

Combining these equations gives us the overall balanced reaction:
\( PbS + O_2 \rightarrow Pb + SO_2 \)
This ensures that we correctly account for every atom in the reaction.

lead (II) sulfide

Lead(II) sulfide, also known as galena, is the primary ore of lead. Its chemical formula is PbS, and it is a mineral with a metallic luster.
In the extraction of lead, galena undergoes two reactions:

• Roasting in oxygen to form lead(II) oxide and sulfur dioxide
• Reaction with lead(II) oxide to produce molten lead and sulfur dioxide

This process is efficient, as it makes use of the existing ore to both source lead and fuel the reactions needed for extraction.

sulfur dioxide

Sulfur dioxide (SO2) is a colorless gas with a pungent odor, often produced in industrial processes like metal extraction.
In the lead extraction cycle from galena, sulfur dioxide is produced both when galena is roasted in oxygen, and when lead(II) oxide reacts with additional galena.

• First reaction: \( 2PbS + 3O_2 \rightarrow 2PbO + 2SO_2 \)
• Second reaction: \( 2PbO + PbS \rightarrow 3Pb + SO_2 \)

Sulfur dioxide must be managed carefully due to its environmental and health impacts.