1- A solution contains 0.317 M potassium nitrite and 0.326 M nitrous acid . The

Question

1- A solution contains 0.317 M potassium nitrite and 0.326 M nitrous acid.
The pH of this solution is:________________.

2- A solution contains 0.285 M sodium nitrite and 0.201 M nitrous acid.
The pH of this solution is : ______________.

3- A solution contains 0.240 M ammonium bromide and 0.303 M ammonia.
The pH of this solution is : ______________.

4- A solution contains 0.242 M ammonium iodide and 0.458 M ammonia.
The pH of this solution is : ______________.

5- A buffer solution is 0.384 M in CH3COOH and 0.323 M in CH3COONa. If Ka for CH3COOH is 1.8×10-5, what is the pH of this buffer solution?

6- A buffer solution is 0.386 M in H3PO4 and 0.250 M in NaH2PO4. If Ka for H3PO4 is 7.5×10-3, what is the pH of this buffer solution?

7- A buffer solution made from CH3COOH and CH3COONa has a pH of 4.44. If pKa for CH3COOH is 4.74, what is the [CH3COO-] / [CH3COOH] in the buffer?

8- The pKa value for H3PO4 is 2.12. What mole ratio of NaH2PO4 to H3PO4 is needed to prepare a buffer with a pH of 1.75?

9- The pKa value for HCO3- is 10.3. What mole ratio of Na2CO3 to NaHCO3 is needed to prepare a buffer with a pH of 10.1?

10- When a 18.6 mL sample of a 0.371 M aqueous hypochlorous acid solution is titrated with a 0.391 M   aqueous sodium hydroxidesolution, what is the pH at the midpoint in the titration?

11- A 21.1 mL sample of a 0.485 M aqueous hypochlorous acid solution is titrated with a 0.347 M aqueous sodium hydroxide solution. What is the pH at the start of the titration, before any sodium hydroxide has been added?

12- A 24.0 mL sample of 0.323 M ethylamine, C2H5NH2, is titrated with 0.284 M nitric acid.
At the titration midpoint, the pH is :________________.

13- A 21.1 mL sample of 0.250 M diethylamine, (C2H5)2NH, is titrated with 0.286 M hydrobromic acid.
The pH before the addition of any hydrobromic acid is:________________.

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14 -

An aqueous solution contains 0.34 M potassium cyanide.

One liter of this solution could be converted into a buffer by the addition of:

(Assume that the volume remains constant as each substance is added.)

a)0.34 mol HI

b)0.17 mol HI

c)0.33 mol KNO3

d)0.33 mol HCN

e)0.17 mol KOH

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15-

An aqueous solution contains 0.22 M ammonia.

One liter of this solution could be converted into a buffer by the addition of:

(Assume that the volume remains constant as each substance is added.)

0.23 mol NH4NO3

0.23 mol HBr

0.22 mol KNO3

0.11 mol KOH

0.11 mol HBr

Explanation / Answer

1. pKa for nitrous acid = 3.39

So, pH = pKa + log [base]/[acid] = 3.39 + log (0.317/0.326) = 3.377

2. pKa for nitrous acid = 3.39

So, pH = pKa + log [base]/[acid] = 3.39 + log (0.285/0.201) = 3.54

3. pKb for NH3 = 4.74

So, pOH = pKb + log [acid]/[base] = 4.74 + log (0.240/0.303) = 4.638

pH = 14 - pOH = 9.26

4. pKb for NH3 = 4.74

So, pOH = pKb + log [acid]/[base] = 4.74 + log (0.242/0.458) = 4.46

pH = 14 - pOH = 9.54

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