Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Rutherford on March 12, 2013, 01:52:19 PM
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Substance A is an anhydrous purple potassium salt. Substance B is the salt of one cation and one anion which in reaction with BaCl2 gives a white precipitate insoluble in dilute acid. When 7.11g of substance A reacts with B in excess in neutral environment, 9.79g of a dark brown oxide is obtained. Determine A and B.
A is certainly KMnO4. 0.045mol of it reacted to form the oxide. The anion in B is SO42-, but here I am stuck. I don't have the reaction equation. What to do now?
Also one quick question: Why is the formula Al(HSO4)3 incorrect?
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Have you noticed 9.79 g is more than 7.11 g? It tells you something.
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The molar mass of the oxide is bigger than that of KMnO4. I can't think of anything else ??? .
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What is the most likely identity of the brown oxide?
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Of manganese probably, and the one that has the biggest molar mass is Mn2O7, so what now?
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No, it is not Mn2O7, and it is quite unlikely product.
What is the most likely identity of a brown oxide that is a product of permanganate reaction?
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MnO2 is usually produces in neutral environment so it could be the oxide. It's amount is 0.1125mol, and the amount of permanganate is 0.045mol, so I don't have enough manganese in the permanganate meaning that B is MnSO4. Using the mass data, I got the following mole ratio: nKMnO4:nMnSO4:nMnO2=2:3:5. The ratio is in agreement with the redox balancing, so the reaction is:
2KMnO4+3MnSO4+2H2O :rarrow: 5MnO2+K2SO4+2H2SO4
I think that this is okay now. Thanks for the help.