I only want the answers, no need for explanation. 1. Which one of the following

Question

I only want the answers, no need for explanation.

1. Which one of the following is NOT a buffer solution?

A.     NH3 and NH4Cl

B.     CH3COOH and CH3COONa

C.     NaHCO3 and Na2CO3

D.     HClO4 and NaClO4

2. When a 25-mL sample of Ba(OH)2 is titrated to the equivalence point with 35.8 mL of 0.150 M HCl, what was the concentration of the original Ba(OH)2?

A.     0.105 M

B.     0.215 M

C.     0.107 M

D.     0.430 M

3. Consider a buffer solution prepared from HCN and NaCN. Which reaction shows how the buffer minimizes pH changes when NaOH is added?

A.     OH- + CN- ® HCNO

B.     H+ + CN- ® HCN

C.     OH- + H+ ® H2O

D.     OH- + HCN ® H2O + CN-

4. On the basis of the information below, a buffer with a pH = 2 can best be made by using

A.     only H3PO4.

B.     H3PO4 and KH2PO4.

C.     KH2PO4 and K2HPO4.

D.     K2HPO4 and K3PO4.

5. The addition of solid NaOH to a saturated aqueous solution of Cu(OH)2 will cause

A.     precipitation of more Cu(OH)2

B.      more Cu(OH)2 to dissolve

C.      no change of the Cu2+ concentration in solution

D.     the Ksp of Cu(OH)2 to decrease

A.     only H3PO4.

B.     H3PO4 and KH2PO4.

C.     KH2PO4 and K2HPO4.

D.     K2HPO4 and K3PO4.

Explanation / Answer

Ans. #1. Correct option- D. HClO4 and NaClO4

A solution of strong acid and its salt does not act as a buffer.

#2. At equivalence point, the total number of moles of H+ from acid is equal to total number of OH- from base.

That is-           x(M1V1), acid = y(M2V2), base

            Where, x = moles of H+ produced per mol acid = 1 for HCl

                        y = moles of OH- produced per mol base = 2 for Ba(OH)2

                        V and M are volume and molarity of respective solution.

Putting the values in above expression-

                        1 (0.150 x 35.8 mL) = 2 x (M2 x 25.00 mL)

                        Or, M2 = (0.150 M x 35.8 mL) / (2 x 25.0 mL)

                        Hence, M1 = 0.1074 M

Therefore, molarity of Ba(OH)2 = 0.1074 M

So, correct option is- C. 0.107 M

#3. Correct option- B. H+ + CN- <-----> HCN

Either the weak acid (HCN) shall donate its proton

Or,

The conjugate base (CN-) shall accept a proton.

#4. Correct option- B. The weak acid H3PO4 and its salt KH2PO4.

The weak acid with its pKa closest to desired buffer pH is preferred. A weak acid and its salt forms the buffer.

#5. Correct option- A. Precipitation od more Cu(OH)2

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