CHEMISTRY MOLE CALCULATIONS

2010-03-21 7:14 am

1. Which of the following, when added to 25 cm3 of 0.1 M hydrochloric acid solution, would change the pH value of the solution

(1) 10 cm3 of 0.1 M nitric acid solution

(2) 15 cm3 of 0.1M sodium chloride solution

(3) 20 cm3 of distilled water

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

2. Which of the following would NOT change the pH of 10cm3 of 1M Hydrochloric acid when added to the acid?

A. 5 cm3 of distilled water
B. 10 cm3 of distilled water
C. 5 cm3 of 2 M hydrochloric acid
D. 20 cm3 of 1M hydrochloric acid

3. In a solution of sodium carbonate and sodium chloride, the concentration of sodium ions is 1.3 M and the concentration of carbonate ions is 0.3 M. What is the concentration of chloride ions?

4. 8.5 g of silver nitrate is dissolved in distilled water and is made up to 250 cm3 in a volumetric flask. What is the concentraion of the solution? (R.A.M : N = 14, O =16, Ag =107.9)

5. Sodium hydroxide solutions react with nitric acid according to the equation

HNO3 (aq) + NaOH (aq) --------> NaNO3 (aq) + H2O (l)

When 20 cm3 of 1 M of nitric acid is mixed with 30 cm3 of 0.5 M sodium hydroxide solution, what is the final pH of the solution?

更新1:

6. To a 1 M hydrochloric acid solution, an equal volume of 4M hydrochloric acid is added. Which of the following are true? (1) the pH value increases. (2) THe electrical conductivity increases. (3) The mass of sodium hydroxide for complete neutralization increases. A. 1 & 2 B. 1 & 3 C. 2 & 3

更新2:

D. ALL OF THE ABOVE

回答 (1)

胡雪8°

2010-03-21 8:06 am

✔ 最佳答案

1. Answer: D。

In 25 cm^3 of 0. M of HCl, concentration of H^+ ions = 0.1 M
If a solution in which the concentration H^+ ions equal to 0.1 M, the pH would not change.
If a solution in which the concentration H^+ ions does not equal to 0.1 M, the pH would change.

(1) Concentration of H^+ ions in HNO3 = 0.1 M
Hence, pH does not change.

(2) NaCl is neutral, concentration of H^+ ions << 0.1 M
Hence, pH changes.

(3) Distilled water is neutral, concentration of H^+ ions << 0.1 M
Hence, pH changes.

2. Answer: D

In 10 cm^3 of 1 M HCl, concentration of H^+ ions = 1 M
If a solution in which the concentration H^+ ions equal to 0.1 M, the pH would not change.
If a solution in which the concentration H^+ ions does not equal to 0.1 M, the pH would change.

A./B. Concentration of H^+ << 1 M. Hence, pH changes.
C. Concentration of H^+ = 0.2 M. Hence, pH changes.
D. Concentration of H^+ = 0.1 M. Hence, pH does not change.

3.
Let a M and b M be the concentrations of Na2CO3 and NaCl respectively.

Concentration of CO3^2- ions: a = 0.3
Concentration of Na^+ ions: 2a + b = 1.3 ..... Hence b = 0.7
Concentration of Cl^- ions = b M = 0.7 M ..... (ans)

4.
No. of moles of AgNO3 = 8.5/(107.9 + 14 + 16*3) = 0.05 mol
Volume = 250 cm^3 = 0.25 dm^3
Concentration = 0.05/0.25 = 0.2 M ..... (answer)

5.
HNO3 + NaOH → NaNO3 + H2O

No. of moles of HNO3 = 1 * (20/1000) = 0.02 mol
No. of moles of NaOH = 0.5 * (30/1000) = 0.015 mol

HNO3 is in excess.
No. of moles of unreacted HNO3 = 0.02 - 0.015 = 0.005 mol
Volume of the solution = 20 + 30 = 50 cm^3 = 0.05 dm^3
Concentration of HNO3 = 0.005/0.05 = 0.1 M
[H^+] = 0.1 M
pH = -log(0.1) = 1 ..... (answer)

6. Answer: C

(1) is false.
pH of 4 M HCl < pH of 1 M HCl

(2) is true.
4 M HCl has a higher concentration of mobile ions.

(3) is is true.
No. of moles of HCl increases after mixing the two acid solutions.

參考: 胡說八

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