Only one direct question exists, so focus narrowly on the practical reasoning: iodide reacts rapidly with manganate(VII), using it up and stopping the ethanedioate reaction.
Brass is an alloy of copper. The percentage by mass of copper in a sample of brass can be determined by a three-stage process.
Stage 1 Oxidation of the copper to copper(II) ions with excess concentrated nitric acid.
Stage 2 Reduction of the copper(II) ions to copper(I) ions with excess iodide ions.
Stage 3 Titration of the iodine produced in Stage 2 against a standard solution of sodium thiosulfate.
In Stage 1, 2.53 g of brass is carefully warmed with 25 cm³ concentrated nitric acid in a 250 cm³ beaker.
The equation for the oxidation of copper metal by nitric acid is shown.
Cu(s) + 4H⁺(aq) + 2NO₃⁻(aq) → Cu²⁺(aq) + 2NO₂(g) + 2H₂O(l)
State what would be seen during the reaction.
green solution formed
- (reddish/yellow) brown fumes formed
Allow any shade of green/blue solution formed Ignore metal would dissolve
Ignore just effervescence