1. The mineral hausmannite, Mn 3 O 4 , which contains both manganese(II) and man
ID: 1036620 • Letter: 1
Question
1. The mineral hausmannite, Mn3O4, which contains both manganese(II) and manganese(III) ions, is formed from heating manganese(IV) oxide to 890°C.
3 MnO2(l) ? Mn3O4(s) + O2(g) (at 890°C)
(a) What is the maximum mass, in megagrams, of Mn3O4 that can be formed from the decomposition of 31.86 Mg of manganese(IV) oxide, MnO2?
Mg
(b) If 22.33 Mg of Mn3O4 is isolated in the decomposition reaction of 31.86 Mg of manganese(IV) oxide, MnO2, what is the percent yield?
%
2. When determining the theoretical yield for a reaction, why must we first determine which reactant is the limiting reactant?
During the reaction the limiting reactant ___(depletes first or depletes last) , after which ___ (no further or additional reaction) takes place and ____(additional product or no additional product) is produced. The amount of ___ (limiting reactant or product) determines the amount of ___(limiting reactant or product produced).
3. The equation for one process for making aluminum fluoride follows. What is the maximum mass, in grams, of aluminum fluoride, AlF3, that can be produced from the complete reaction of 3.0???103 g of aluminum hydroxide, Al(OH)3, with 2.9???103 g of H2SiF6?
2 Al(OH)3 + H2SiF6 ? 2 AlF3 + SiO2 + 4 H2O (at 100°C)
_____g?
4. Uranium is distributed in a form called yellow cake, which is made from uranium ore. In the second step of the reactions that form yellow cake from uranium ore, uranyl sulfate, UO2SO4, is converted to (NH4)2U2O7.
2 UO2SO4 + 6 NH3 + 3 H2O ? (NH4)2U2O7 + 2 (NH4)2SO4
(a) What is the maximum mass, in kilograms, of (NH4)2U2O7 that can be formed from the reaction of 150. kg of water and 150. kg of ammonia with 490. kg of UO2SO4?
___ kg
(b) Explain why two of these substances are in excess and one is limiting.
---Select--- Uranyl sulfate or Ammonia Water and ---Select--- uranyl sulfate ammonia water are both ---Select--- (expensive or cheap), ---Select--- plentiful rare , and ---Select--- easily separated hard to separate from ---Select--- uranyl sulfate ammonia water .
5. Calcium carbide, CaC2, reacts with water to form acetylene, C2H2, and calcium hydroxide.
(a) Write a balanced equation for this reaction.
(b) If you were designing the procedure for producing acetylene from calcium carbide and water, which of the reactants would you have as the limiting reactant? Why?
It would be best to have _____ (calcium or carbide water) in excess as it is _____ (cheap or expensive) , _____ (plentiful or rare) , and safer to handle than _______ (water or calcium carbide) .
(c) Assuming 100% yield from the limiting reactant, what are the amounts of CaC2 and water that you would combine to form 151 g of C2H2?
exactly ____ g of (calcium carbide or water) ? well over _____g of ---Select--- (calcium carbide or waterExplanation / Answer
1)
a)
Molar mass of MnO2,
MM = 1*MM(Mn) + 2*MM(O)
= 1*54.94 + 2*16.0
= 86.94 g/mol
mass of MnO2 = 31.86 Mg = 31860000 g
mol of MnO2 = (mass)/(molar mass)
= 31860000/86.94
= 366460 mol
Balanced chemical equation is:
3 MnO2(l) ? Mn3O4(s) + O2(g)
According to balanced equation
mol of Mn3O4 formed = (1/3)* moles of MnO2
= (1/3)* 366460
= 1.22*10^5 mol
Molar mass of Mn3O4,
MM = 3*MM(Mn) + 4*MM(O)
= 3*54.94 + 4*16.0
= 228.82 g/mol
mass of Mn3O4 = number of mol * molar mass
= 1.22*10^5*228.82
= 2.80*10^7 g
= 28.0 Mg
Answer: 28.0 Mg
b)
% yield = actual mass*100/theoretical mass
= 22.3*100/28.0
= 79.9 %
Answer: 79.9 %
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