F.5 CHEM MC

2010-10-18 9:18 am

1. 4.00 g of sodium hydroxide is dissolved in 500 cm^3 of water to make a solution. What is the concentration of the solution?

A. 8.00 g dm^-3
B. 0.200 M
C. slightly higher than 0.200 M
D. slightly lower than 0.200 M

Why the answer is D?
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2. What is the concentration of a solution formed by dissolving 28g of anhydrous iron(II) sulphate in 125.0 cm^3 of solution?

A. 1.47 M
B. 0.00147 M
C. 0.221 M
D. 22.1 M

Why is the answer is A?
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3. Which of the following solutions contain the same amount of ions?
(1) 36 cm^3 of 1.0 M sodium nitrate solution
(2) 30 cm^3 of 1.5 M sodium hydroxide solution
(3) 24 cm^3 of 1 M potassium sulphate solution

A. (1) and (2) only
B. (1) and (3) only
C. (2) and (3) only
D. (1),(2) and (3)

Why the answer is B?
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Thanks very much!!! :D

回答 (1)

六呎將軍

2010-10-18 7:59 pm

✔ 最佳答案

1) Since 4.00 g of sodium hydroxide has a little volume, say △V, thus the resulting volume after dissolving it in 0.5 dm3 of water will be (0.5 + △V) dm3.

Hence the conc. is (with 4.00g of NaOH having 0.1 mole):

0.1/(0.5 + △V) < 0.2 M slightly

So ans = D

2) Molar mass of iron(II) sulphate = 56.3 + 32.1 + 4 x 16 = 152.4 g/mol

This no. of moles of 28 g of it = 28/152.4 = 0.1837

Conc. = 0.1837/0.125 = 1.47 M

So ans = A

3) For (1), no. of moles of sodium nitrate = 1 x 0.036 = 0.036

Each mole of sodium nitrate contains 1 mole of sodium ions and 1 mole of nitrate ions, i.e. a total of 2 moles of ions

Hence no. of moles of ions = 2 x 0.036 = 0.072

For (2), no. of moles of sodium hydroxide = 1.5 x 0.03 = 0.045

Each mole of sodium hydroxide contains 1 mole of sodium ions and 1 mole of hydroxide ions, i.e. a total of 2 moles of ions

Hence no. of moles of ions = 2 x 0.045 = 0.09

For (3), no. of moles of potassium sulphate = 1 x 0.024 = 0.024

Each mole of potassium sulphate contains 2 mole of sodium ions and 1 mole of sulphate ions, i.e. a total of 3 moles of ions

Hence no. of moles of ions = 3 x 0.024 = 0.072

Hence ans = B

參考: Myself

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