45. If the concentration of Off in an aqueous solution is 1.4 X 10-7 M. concentr

Question

45. If the concentration of Off in an aqueous solution is 1.4 X 10-7 M. concentration of H30 is B) 1.0× 10-7M O 1.4 x 10-7 M D)7.1x10-8M. E) 1.3 10-8 46, Which solution is basic? A) [H30*)#1.0 x 10-4 B) 30 1.0 x 10-7 C) [H30-1.?? 10-10 D) [OH-)-1.0 x 10-7 E) tot.)-1.0 x 10-10 47. thich solution contaíning an equsl munber of mol substancen is a buffer? A) HCl nnd NaCl B) IN02 and HND E More than one of the solutions is a buffer. 48. Al1 of the following statesents are general properties of organte cospounds except: A) the honds are covalent. b) they have relatively low bolling points O they have linited or no water solubility D) they usually behave as electrolytes in solution. E) they have relatively low melting points

Explanation / Answer

Answer:

(45) The relationship between H3O^+ and OH^- is

[H3O^+][OH^-]=1x10^-14

Given [OH^-]=1.4x10^-7 M,

then [H3O^+]=(1x10^-14)/(1.4x10^-7)

[H3O^+]=7.1x10^-8 M.

So option (D) is correct.

(46) We know that the solution pH<7, then the solution is acedic.

If pH>7, then the solution is basic and pH=7, then the solution is neutral.

pH=-log[H3O^+], pOH=-log[OH^-] and pH+pOH=14.

Option (C) is basic, since [H3O^+]=1x10^-10 M,

Then pH=- log(1x10^-10)=10.

Therefore pH=10 (pH>7) so it is basic.

In option (A), [H3O^+]=1x10^-4, then pH=-log(1x10^-4)

pH=4 (<7) so it is acedic.

In option (B), [H3O^+]=1x10^-7, pH=- log(1x10^-7)

pH=7, so it is neutral.

In option (D), [OH^-]=1x10^-7, pOH=-log(1x10^-7)=7

pH=14-pOH=14-7=7. So it also neutral.

In option (E), [OH^-]=1x10^-10, pOH=- log(1x10^-10)=10.

pH=14-pOH=14-10=4, so it is also acedic.

Finally option (C) is correct.

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