Atomic masses can be determined by electrolysis. In one hour, a current of 0.872 amperes deposits o.562 grams of a certain metal, M, which is present in solution as M^3+ ions.
a) what is the atomic mass of the metal?
b) Identify the metal.
Electrolysis to calculate atomic mass- PLEASE HELP?
2016-06-22 9:24 am
回答 (1)
2016-06-22 9:42 am
(a)
Amount of charges passed = I t = (0.872 A) × (3600 s) = 3139 C
I mole of e⁻ carries 96500 C of charges.
No. of moles of e⁻ passed = (3139 C) / (96500 C/mol) = 0.03253 mol
M³⁺(aq) + 3e⁻ → M(s)
OR: Mole ratio e⁻ : M = 3 : 1
No. of moles of M deposited = (0.03253 mol) × (1/3) = 0.01084 mol
Molar mass of M = (0.562 g) / (0.01084 mol) = 51.8 g/mol
Atomic mass of M = 51.8
(b)
The metal may be chromium.
This is because the atomic mass of chromium is 52.00, which is close to 51.8, and chromium usually forms Cr³⁺ ions.
Amount of charges passed = I t = (0.872 A) × (3600 s) = 3139 C
I mole of e⁻ carries 96500 C of charges.
No. of moles of e⁻ passed = (3139 C) / (96500 C/mol) = 0.03253 mol
M³⁺(aq) + 3e⁻ → M(s)
OR: Mole ratio e⁻ : M = 3 : 1
No. of moles of M deposited = (0.03253 mol) × (1/3) = 0.01084 mol
Molar mass of M = (0.562 g) / (0.01084 mol) = 51.8 g/mol
Atomic mass of M = 51.8
(b)
The metal may be chromium.
This is because the atomic mass of chromium is 52.00, which is close to 51.8, and chromium usually forms Cr³⁺ ions.
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