Consider the following data on some weak acids and weak bases: acid base CI name

Question

Consider the following data on some weak acids and weak bases: acid base CI name formula name formula 10 hydrocyanic acid HCN 4.9 x 10 ethylamineC2H5NH2 6.4x1 4 nitrous acid HNO | 4.5% 10 hydroxylamine HONH 21.1 x 10 Use this data to rank the following solutions in order of increasing pH. In other words, select a '1' next to the solution that will have the lowest pH, a '2' next to the solution that will have the next lowest pH, and so on solution pH 0.1 M HONH3CI choose one 0.1 M KCN choose one 0.1 M C2HsNH3Br choose one 0.1 M NaNO2 choose one

Explanation / Answer

for these are the salt.

for salt of strong base and weak acid.

PH = 0.5 * PKw + 0.5 * PKa + 0.5 * log C

For 0.1 M KCN,

PKa of HCN = - log (4.9 * 10^-10) = 9.31

for 0.1 M NaNO2:

PKa of HNO2 = -log (4.5 * 10^-4) = 3.35

for weak base and strong acid,

PH = 0.5 * PKw - 0.5 * PKb - 0.5 * log C

0.1 M HONH3Cl:

PKb of HONH2 = - log (1.1 * 10^-8) = 7.96

0.1 M C2H5NH3Br :

PKb of C2H5NH2 = - log (6.4 * 10^-4) = 3.19

increasing PH order is

0.1 M HONH3Cl < 0.1 M C2H5NH3Br < 0.1 M NaNO2 < 0.1 M KCN

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