11. Assuming equal concentrations of conjugate base and acid, which one of the f

ID: 956416 • Letter: 1

Question

11. Assuming equal concentrations of conjugate base and acid, which one of the following mixtures suitable for making a buffer solution with an optimum pH of 4.6-4.8? A CH,coo,NaCH,CooH (k 1.8 x 10 B. x 10 c. NaoclHoci (K. 3.2 x 104 D. (Ka 4.5 x 10 E. NaCl/HCI 2. The pH at the equivalence point of a titration may differ from 7.0 due to A the initial concentration of the standard solution. B, the indicator used. C, the self-ionization of H2O. D. the initial pH of the unknown. E. hydrolysis of the salt formed. A titration of an acid and base to the equivalence point results in a noticeably acidic solution. It is likely this titration involves A. a strong acid and a weak base. B. a weak acid and a strong base. C, a weak acid and a weak base (where Ka equals Kb). D. a strong acid and a strong base. Bromothymol blue is a common acid-base indicator. It has a Ka equal to 1.6 x 10 Its un-ionized form is yellow and its conjugate base is blue. What color would a solution have at pH- 4.8? A. Yellow B. Blue C. Red D. Green What is the conjugate base of HPO42? H3PO4 H2PO4 PO. OH

Explanation / Answer

11) pH= pKa + log [conjugated base]/[acid]

If the concentrations of conjugated base and acid are the same log [conjugated base]/[acid] is 0.

So pH=pKa

a) pKa= -log Ka= 4.74= pH

b) pKa= 9.25

c) pKa= 7.49

d) pKa= 3.35

e) this option can´t be because to make a buffer you need a weak acid or a weak base, and HCl is a stong acid.

So the correct option is A).

12) The correct option is E. Some salt dissociate and react with water leaving H+ groups or OH- groups depending of the nature of the salt.

13) The correct answer is A.

For example HCl + NH3

HCl + NH3 ----> NH4Cl (salt)

Cl- is the conjugated base of a strong acid, this means that Cl- is a weak base and don´t affect pH.

NH4+ is the conjugated acid of a weak base, this means that NH4+ is a strong acid and will react with water.

NH4+ + H2O <-----> NH3 + H3O+

That H3O+ formed modifies pH and gives an acidic solution at the equivalence point.

14) the correct answer is A.

15) your answer is correct

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11. Assuming equal concentrations of conjugate base and acid, which one of the f

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