Question

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

A) 0.550M

B) 0.100M

C) 1.2x10^-2 M

D) In which cases can you not make the simplifying assumption that x is small?
only in (b)
only in (a)
in (b) and (c)
in (a) and (b)

PS: Express your answer to two decimal places

Answer 1

Answer 2

The pH of HNO, has to be determined for different concentrations. The ICE table will be used to determine the amount of H ions dissociated by the nitric acid. Once the concentration of dissociated H ions is determined, the following formula is used to get the pH values: 1: pHlog[H] The acid dissociation constant of nitric acid is 4.6x 10 a) 0.550 M HNO, concentration H30NO HNO2 Н.о Initial 0.550 0 0 Change +x +x -X Equilibrium 0.550-x The concentration of water will not be considered as it is present in excess and remains constant NO:Ho HNO2 [xx] [0.550-x] 4.6x10 x=0.0156 M Thus, the concentration of H рH--1og [н] -log [0.0156] ions is 0.0156 M. Determine the pH as shown below: = 1.81 b) 0.100 M HNO, concentration HNO2 NO7 Н.о но Initial 0.100 0 0 Change +x +x -X Equilibrium 0.100-x X The concentration of water will not be considered as it is present in excess and remains constant

[NO;THo HNO2] 4.6x10 [0.100-x] x 0.00655 M Thus, the concentration of H pH-log H - -log[0.00655] ions is 0.0156 M. Determine the pH as shown below 2.18 c) 1.2x10 M HNO, concentration H,0 NO HNO2 H2O + 12x10 Initial 0 0 Change +x x -x 1.2x10-x Equilibrium The concentration of water will not be considered as it is present in excess and remains constant NO:Ho] HNO 4.6x10 1.2x10-x x 0.00213 M Thus, the concentration of H pH-log H] --log [0.00213] ions is 0.0156 M. Determine the pH as shown below 2.67

To make the assumption for value of x, 5% rule is considered. According to 5% rule, if the value of x is less than 5% of the value of given concentration of the acid, then it can be assumed small. If the value of x is more than 5 % of given concentration of the acid, then it cannot be assumed small Determine the 5 % of all the given concentration of acids. Determined Whether Given value of x value of x S. No. 5% of given concentration concentration (see above calculations) Neglected (in M) or not 5 -0.0275 100 0.550x neglected A 0.550 0.0156 5 0.005 100 Not 0.100 x 0.100 0.006 neglected 5 0.0006 Not 1.2x10 1.2x102x C 0.00216 neglected 100 The value ofx in part b and c is more than the 5 % of given concentration of the acid; thus, they can't be neglected. C C Hence, in (b) and (c), the simplifying assumption that x is small cannot be made