A fish-farm worker treats a water tank using potassium permanganate crystals. Fig. 1 shows a sealed reaction vessel containing the crystals and a solution o...
Question 1 Report
A fish-farm worker treats a water tank using potassium permanganate crystals. Fig. 1 shows a sealed reaction vessel containing the crystals and a solution of hydrogen peroxide. The vessel is connected to a gas syringe so that oxygen produced can be retained and measured.
(a) Name the gas in the syringe. [1]
(b) Describe a test for this gas and its positive result. [2]
(c) Explain why the gas syringe must remain attached when comparing masses before and after the reaction. [2]
Fig. 1 shows a medicines technician mixing aqueous silver nitrate with sodium chloride solution inside a stoppered conical flask. A white solid forms. The flask is weighed before mixing, and then gently tilted so the solutions combine without removing the stopper.
(a) Name the white solid made. [1]
(b) Complete the balanced equation: AgNO3 + NaCl → AgCl + ________. [1]
(c) Use the masses to calculate the mass of sodium nitrate if 8.50 g of reactants produce 2.87 g of silver chloride. [2]
(d) Explain why the mass does not change even though a solid appears. [1]
Answer Details
Hydrogen peroxide reaction
- The gas collected is oxygen. [1]
- Insert a glowing splint into the gas. A positive result is that the splint relights. [2]
- The syringe must stay attached because otherwise oxygen escapes. Escaped gas makes the measured mass lower even though mass is conserved when all products are included. [2]
Silver nitrate and sodium chloride
- The white solid is silver chloride. [1]
- \[\mathrm{AgNO_3+NaCl\rightarrow AgCl+NaNO_3}\] [1]
- \[8.50\text{ g}-2.87\text{ g}=5.63\text{ g}\]
Mass of sodium nitrate = 5.63 g. [2] - The atoms in the solutions are rearranged to form a precipitate, but they all remain in the stoppered flask. Therefore its mass does not change. [1]
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