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22 Lead is most commonly extracted from an ore called galena, PbS - OCR Gateway - GCSE Chemistry - Question 22 - 2019 - Paper 3
Question 22
22 Lead is most commonly extracted from an ore called galena, PbS. (a) Extracting lead from the galena ore involves two steps. Step 1: The galena ore is roasted in a... show full transcript
Worked Solution & Example Answer:22 Lead is most commonly extracted from an ore called galena, PbS - OCR Gateway - GCSE Chemistry - Question 22 - 2019 - Paper 3
Step 1
Draw a labelled reaction profile diagram for an exothermic reaction.
Answer
To illustrate an exothermic reaction, the reaction profile diagram should depict the reactants starting at a certain energy level. The curve then decreases as the reaction proceeds, indicating that energy is released, reaching a lower energy level at the products. The activation energy (the peak of the curve) must be labelled, along with the energy change, which is the difference in energy between the reactants and products, indicating a negative value, showing that energy is released.
Step 2
Explain, in terms of electron transfer, why carbon is called a reducing agent in this reaction.
Answer
In the reaction PbO + C → Pb + CO, carbon acts as a reducing agent because it donates electrons to the lead oxide (PbO). As it provides electrons, it reduces the oxidation state of lead, converting PbO (where lead is in the +2 state) into Pb (where lead is in the 0 state). This transfer of electrons implies that carbon is helping in the reduction process.
Step 3
Step 4
How many moles of lead nitrate would be produced if 20.7g of lead reacts with nitric acid?
Answer
To calculate the number of moles of lead nitrate produced:
- Calculate the molar mass of lead (Pb) which is approximately 207 g/mol.
- Calculate the number of moles of lead from the mass given: ext{Moles of Pb} = rac{20.7 ext{ g}}{207 ext{ g/mol}} \\ = 0.1 ext{ moles}
- From the balanced equation, 3 moles of Pb produce 3 moles of Pb(NO₃)₂. Therefore, the moles of lead nitrate produced are also 0.1 moles, when rounded to 2 significant figures.