FORM 4 CHEMISTRY MC(20分)

1.
Let y g mol-1 the mass of 1 mol of O atoms.
Then, the mass of 1 mol of S atoms = 2y g mol-1


a) incorrect
At room temperature and pressure, sulphur is a solid while oxygen is a gas. Therefore, they have different molar volume, and their volumes are thus not equal to each other.

b) correct
From a), no. of moles of 2 g of S = (1/y) mol
No. of atoms of 2 g of S = mol * (Avogadro number) = (L/y) atoms

From a), no. of moles of 1 g of O = (1/y) mol
No. of atoms of 1 g of O = mol * (Avogadro number) = (L/y) atoms

c) incorrect
No. of atoms in 1 mol of S atoms = mol * (Avogadro number) = L atoms
No. of atoms in 1 mol of O atoms = mol *(Avogadro number) = L atoms
The no. of atoms in 1 mol of S atoms is NOT twice that in 1 mol of O atoms.

No. of atoms in 1 mol of S8 molecules = 8L atoms
No. of atoms in 1 mol of O2 molecules = 2L atoms
The no. of molecules in 1 mol of S8 molecules is NOT twice that in 1 mol of O2­ molecules.

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2. The answer is C.

Molar mass of N2 gas = 14*2 = 28 g mol-1
No. of moles of 4 g of N2 = mass/(molar mass) = 4/28 = (1/7) mol
No. of molecules in 4 g of N2 = (1/7)L = (L/7) molecules
Hence, y = L/7

Molar mass of O2 gas = 16*2 = 32 g mol-1
No. of moles of 64 g of O2 = mass/(molar mass) = 64/32 = 2 = 14(1/7) = 14y

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3.
The answer is b.

No. of O3 molecules in 1 mol of O3 = 1 * L = L molecules
No. of O atoms in 1 mol of O3 = L * 3 = 3L atoms
Hence, x = 3L

No. of O2 molecules in 1 mol of O2 = 1 * L = L molecules
No. of O atoms in 1 mol of O2 = L * 2 = 2L = 2*(3L)/3 = 2x/3

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4.
The answer is c.

Ca is a metal while Br is a non-metal.
Therefore, CaBr2 is an ionic compound, and each mol of CaBr2 contains 1 mole of Ca2+ cations and 2 mol of Br- anions.

a) incorrect
This is because CaBr2 is ionic, which contains ions, but not molecules.

b) incorrect
This is because CaBr2 contains 1 mol of Ca2+ cations, but not 2 mol.

c) correct
This is because CaBr2 contains 2 mol of Br- anions.

d) incorrect
This is because CaBr2 is ionic, which contains ions, but not atoms.
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1a)Wrong. At room temp and pressure, sulphur is solid and oxygen is gas. Their molar volume have great different.
b)Correct
c)Wrong. 1 mole of any substances has same number of atoms
2)molecules are present=y/(4/28)*(64/32)=14y (C)
3)one mole of oxygen contain= x/3*2=2x/3 (B)
4a)Wrong.CaBr2 is ionic compound. It has no molecules.
b)Wrong.One mole of CaBr2 contains one mole cations(Ca2+)
c&d)Corrcet