Brass is an alloy consisting mainly of copper and zinc. To determine the percentage of copper in a sample of brass, 2.63 g of the brass was dissolved in concentrated nitric acid and the solution diluted to 250 mL in a standard flask. Excess potassium iodide was added to 25.0 mL of this solution, iodine being produced according to the equation: 2Cu2+(aq) + 4I–(aq) → 2CuI(s) + I2(aq) The iodine formed was titrated with 0.1000 M sodium thiosulfate solution, Na2S2O3(aq), the volume required for complete reaction being 24.8 mL. I2(aq) + 2S2O32–(aq) → 2I–(aq) + S4O62–(aq) colorless colorless (a) Which species in the first equation is oxidised? (b) How could the end-point for the titration be made more obvious? (c) How many moles of sodium thiosulfate were required in the titration? (d) Calculate the percentage by mass of copper in the sample of brass.
Brass is an alloy consisting mainly of copper and zinc. To determine the percentage of copper in a sample of brass, 2.63 g of the brass was dissolved in concentrated nitric acid and the solution diluted to 250 mL in a standard flask. Excess potassium iodide was added to 25.0 mL of this solution, iodine being produced according to the equation: 2Cu2+(aq) + 4I–(aq) → 2CuI(s) + I2(aq) The iodine formed was titrated with 0.1000 M sodium thiosulfate solution, Na2S2O3(aq), the volume required for complete reaction being 24.8 mL. I2(aq) + 2S2O32–(aq) → 2I–(aq) + S4O62–(aq) colorless colorless (a) Which species in the first equation is oxidised? (b) How could the end-point for the titration be made more obvious? (c) How many moles of sodium thiosulfate were required in the titration? (d) Calculate the percentage by mass of copper in the sample of brass.
Chemistry & Chemical Reactivity
9th Edition
ISBN:9781133949640
Author:John C. Kotz, Paul M. Treichel, John Townsend, David Treichel
Publisher:John C. Kotz, Paul M. Treichel, John Townsend, David Treichel
Chapter4: Stoichiometry: Quantitative Information About Chemical Reactions
Section: Chapter Questions
Problem 125IL: You wish to determine the weight percent of copper in a copper-containing alloy. After dissolving a...
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Chemical Reactions and Equations
When a chemical species is transformed into another chemical species it is said to have undergone a chemical reaction. It consists of breaking existing bonds and forming new bonds by changing the position of electrons. These reactions are best explained using a chemical equation.
Question
Brass is an alloy consisting mainly of copper and zinc. To determine the percentage of copper in a sample of brass, 2.63 g of the brass was dissolved in concentrated nitric acid and the solution diluted to 250 mL in a standard flask. Excess potassium iodide was added to 25.0 mL of this solution, iodine being produced according to the equation:
2Cu2+(aq) + 4I–(aq) → 2CuI(s) + I2(aq)
The iodine formed was titrated with 0.1000 M sodium thiosulfate solution, Na2S2O3(aq), the volume required for complete reaction being 24.8 mL.
I2(aq) + 2S2O32–(aq) → 2I–(aq) + S4O62–(aq)
colorless colorless
(a) Which species in the first equation is oxidised?
(b) How could the end-point for the titration be made more obvious?
(c) How many moles of sodium thiosulfate were required in the titration?
(d) Calculate the percentage by mass of copper in the sample of brass.
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