有幾條chem 的mole concept題目 唔識做
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1.What mass of iron is obtained when 0.20 mol of iron(III) oxide are completely reduced by carbon?
answer is 11.2 g
2.The following equation represents the reaction of an oxide of iron with hydrogen:
Fe3O4(s) + 4H2(g)--->3Fe(s) + 4H2O(l)
What mass of iron would be obtained if 2.32 g of the oxide was used up in the reaction?
(Relative atomic masses: Fe=56, O=16)
answer is 1.68g
3. 2.4 g of oxygen contains x atoms at room conditions. How many atoms are present in 12 g of helium?
answer is 20x
4.If 1 mole of YO3 contains the same number of atoms as 72 g of YH4, what is the relative atomic mass of Y?
answer is 86
about F4 chem mole concept
2008-12-02 7:05 am
回答 (1)
2008-12-02 10:15 am
✔ 最佳答案
1.Molar mass of Fe = 56 g mol-1
2Fe2O3 + 3C → 4Fe + 3CO2
Mole ratio Fe2O3 : Fe = 2 : 4 = 1 : 2
No. of moles of Fe2O3 used = 0.2 mol
No. of moles of Fe formed = 0.2 x 2 = 0.4 mol
Mass of Fe formed = mol x (molar mass) = 0.4 x 56 = 22.4 g
(The given answer 11.2 g is incorrect.)
(If 0.10 mol of iron(III) oxide is used instead, the answer is 11.2 g.)
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2.
Molar mass of Fe = 56 g mol-1
Molar mass of Fe3O4 = 56x3 + 16x4 = 232 g mol-1
Fe3O4 + 4H2 → 3Fe + 4H2O
Mole ratio Fe3O4 : Fe = 1 : 3
No. of moles of Fe3O4 used = mass/(molar mass) = 2.32/232 = 0.01 mol
No. of moles of Fe formed = 0.01 x 3 = 0.03 mol
Mass of Fe formed = mol x (molar mass) = 0.03 x 56 = 1.68 g
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3.
Molar mass of O atoms = 16 g mol-1
Molar mass of He atoms = 4 g mol-1
Avogadro number = L
No. of moles of O atoms = mass/(molar mass) = 2.4/16 = 0.15 mol
No. of O atoms = 0.15L
Hence, 0.15L = x
L = x/0.15
No. of moles of He atoms = mass/(molar mass) = 12/4 = 3 mol
No. of He atoms = 3L = 3(x/0.15) = 20x
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4.
Let M the relative atomic mass of Y.
Thus, molar mass of YH4 = (M + 4) g mol-1
Avogadro number = L
In 1 mol of YO3:
Each mol of YO3 contains 4 mol of atoms.
No. of moles of atoms = 4 mol
No. of atoms = 4L atoms
In 72 g of YH4:
No. of moles of YH4 = [72/(M + 4)] mol
Each moles of YH4 contains 5 mol of atoms.
No. of moles of atoms = 5[72/(M + 4)] = [360/(M + 4)] mol
No. of atoms = [360/(M + 4)]L = [360L/(M + 4)] atoms
Given that: 360L/(M + 4) = 4L
4(M + 4) = 360
M + 4 = 90
M = 86
The relative atomic mass of Y is 86.
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