Determine the pH of an HNO2 solution of each of the following concentrations. A)

Question

Determine the pH of an HNO2 solution of each of the following concentrations. A) 0.500M B) 0.110M C) 1.10x10^-2M D) In which cases can you not make the simplifying assumption that x is small? A)only in (b) B) only in (a) C) in (b) and (c) D) in a) and (b) Determine the pH of an HNO2 solution of each of the following concentrations. A) 0.500M B) 0.110M C) 1.10x10^-2M D) In which cases can you not make the simplifying assumption that x is small? A)only in (b) B) only in (a) C) in (b) and (c) D) in a) and (b) A) 0.500M B) 0.110M C) 1.10x10^-2M D) In which cases can you not make the simplifying assumption that x is small? A)only in (b) B) only in (a) C) in (b) and (c) D) in a) and (b)

Explanation / Answer

HNO2 <---> H+ + NO2-

HNO2 will dissociate x amount into x amount of H+ and OH-.

ka = 4.00E-4

ka = [H+][NO2-] /[HNO2]

A,

4E-4 = x^2 / (.50-x)

x=0.0141M=[H+] = [NO2-]

pH=1.85

B,

4E-4 = x^2 / (.110-x)

x=[H+] = [NO2-]=0.081

pH=1.09

C,4E-4 = x^2 / (1.10x10^-2M-x)

x=[H+] = [NO2-] =0.0445

pH=1.31

at higher concentration we can assume x is small

so D,in b and c we cannot assume x is small

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