F4 Chemistry Questions(12Q=10MC + 2LQ)

2007-02-22 9:43 pm

1)Which of the following statements are correct?
a.1 mole is the quantity of a substance that contains Avogadro number of particles
b.1 mole of Zn and 1 mole of Fe have different masses
c.The molar mass of a substance is the mass in g of 1 mole of it
2)The Avogadro's no.
a.has the numerical value of 6.02*10^23
b.varies with temperature and pressure
c.is represented by the symbol L

更新1:

3)1 mole of a substance is a.the amount equal to the formula mass of the substance in g b.the mass of a substance divided by its molecular mass c.the amount = its molar mass 4)2g of O gas contains x molecules, then 28g of N gas present(N=14.0,O=16.0) a.x b.4x c.8x d.16x

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5)17.75g of Cl contain x molecules, then 8g of Sulphur dioxide contain(O=16.0,S=32.0,Cl=35.5) a.x/4 b.x/2 c.x d.2x 6)The molecular formula of a gas is X3. If the Avogadro's no. is L mol^-1, how many atoms are there in 48g of X3?(X=16.0) a.1/2L b.L c.2L d.3L

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7)2g of Carbon monoxide gas contain x molecules, how many molecules are present in 1g of H gas?(H=1.0,C=12.0,O=16.0) a.3.5x b.5.5x c.7x d.11x 8)Molecular formula of a gaseous element X is X2,then no. of molecules in 112g of the gas(X=14.0,L=6.02*10^23) a.4 b.8 c.4*L d.8*L

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9)3 moles of magnesium chloride contains a.3moles of molecules b.6moles of cations c.6moles of anions d.9moles of atoms 10)An oxide of X has the formula X2O3.14.28g of this contains 7.56 of X, then the relative atomic mass of X(O=16.0) a.12.0 b.18.0 c.27.0 d.36.0

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LQ: 11)5.1g of Cacl2．nH20 gives 5.0 g of water on strong and becomes CaCl2 on heating.Find n.(O=16.0,Cl=35.5,Ca=40.0,Cu=63.5)

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12)A hydrated salt of copper contains 63.9% by mass of the anhydrous salt.The anhydrous salt has the following percentage composition by mass: copper 39.8%, sulphur 20.0%, oxygen 40.2%. Find the empirical formula of the hydrated salt. (O=16.0,S=32.0,Cl=35.5,Ca=40.0,Cu=63.5)

更新7:

**Last notice: the informations about the elements in the brackets are the Atomic masses of the elements

回答 (1)

用戶109005

2007-03-04 3:43 am

✔ 最佳答案

1. A, B, C
2. A, C
3.A
4.D
5.B
6.B
7.C
8.C
9.C
10.C

11. The molar mass of CaCl2
= 40+35.5*2 g/mol
=111 g/mol

The amount of CaCl2 in 5.1g of CaCl2．nH2O
= (5.1-5)g
=0.1g

Therefore the number of mole of CaCl2
= (0.1/111) mol
=1/1110 mol

Amount of H2O = 5.0 g
Therefore the number of mole of H2O = 5/18 mol

___________CaCl2________________H2O______________________
Mole________1/1110 mol____________ 5/18
Mole Ration ____1_________________around 278 (277.777777777777)

Therefore the formula is CaCl2．278H2O

THE QUESTION MAY BE WRONG AS IT IS IMPOSSIBLE TO HAVE SUCH COMPOUND

12. Let's consider the empirical formula of the anhydrous salt first.

We will consider there's 100g of the anhydrous salt, therefore there are 39.8g, 20g and 40.2g of copper, sulphur and oxygen respectively.
________________Cu______________S_______________O
mass___________39.8 g____________20______________40.2
number of mole__398/635____________5/8____________201/80
Mole Ratio____around 1(1.003)_______1___________around 4 (4.02)
(We'll divide the numbers with the smallest mole)

Therefore the empirical formula is CuSO4

The molar mass of CuSO4 is 159.5 g/mol

Let's consider the hydrated salt

In 100g of CuSO4．nH2O has 63.9 of CuSO4 and the rest are H2O, which is 36.1g

_____________CuSO4______________________H2O
______________63.9_______________________36.1
Mole_________639/1595____________________361/180
Mole Ration______1________________________around 5 (5.0060)

Therefore the empirical formula of the hydrated salt is CuSO4．5H2O

參考: Chem knowledge

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