l Verizon LTE 5:24 PM * 42%.. instructure-uploads,s3.amazonaws.com 18. Calculate
ID: 692041 • Letter: L
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l Verizon LTE 5:24 PM * 42%.. instructure-uploads,s3.amazonaws.com 18. Calculate pH of 0.1 M solution of a weak acid with Ka = 1.3 19. What will be the pH of the solutions of the following salts? a) NaNO, b) NH,CI c)CH COOK 20. Lewis theory: Which of the compounds or ions below is a Lewis acid? a. NH, b. Co in Co(NH 21. Calculate the pH of 0.15 M solution of Na HPO,if Ka( H.PO?) = 6.3x 10. 22. An acid-base equilibrium system is created by dissolving 0.20mol CH COOH in water and diluting the resulting solution to a volume of 1.0 L. What is the effect of adding 0.020 mol CH,COO (aq) to this solution? How will pH change (calculate pH before and after the addition. Ka of CH,COOH is 1.76 x10)? How will concentrations of CH,COOH and CHCoo at equilibrium change? 23. Which of the following combinations would be best to buffer an aqueous solution at a pH of 7.5? Why? a. H,PO, and H PO, K7.5 10 b. HNO, and NO., K, = 4.5 , 10. c. CH,CO,H and CH,COO, K,-1.8 d. H,PO, and HPO, K . 10 e. NH, and NH, K, = 5.7 , 101. 10Explanation / Answer
18) The pH of a weak acid is calculated by
pH = 1/2[ pKa -logC]
given Ka = 1.3 x10-5 , thus pKa = 4.886
Concentration C of acid = 0.1
Thus pH = 1/2[ 4.886 - log 0.1]
= 2.943
19) The pH of the salt is known from which acid and base they are formed.
Salts of weakacids and /or weak bases undergo hydrolysis and have pH less or more than 7.
A salt of strong acid and strong base does not hydrolyse and has pH = 7.
a) NaNO3 -salt of strong acidHNO3 and strong base NaOH
thus no hydrolysis and pH =7
b) NH4Cl
salt of weak base NH4OH and strong acid HCl.
Thus the cation NH4+ undergoes hydrolysis to give acidic solution.
NH4+ + H2O -----------> NH4OH + H+
Thus the pH of the solution is less than 7
c) CH3COOK
salt of weak acid CH3COOH and strong base KOH
undergoes anionic hydrolysis
CH3COO- + H2O ----------> CH3COOH + OH-
Thus pH >7
20) A Lewis acid is a species that can accept a pair of electrons and
a Lewis base is a species that can donate apair of electrons
a) NH3 is a Lewis base as it can donate a pair of electrons.
b) Co+3 in [Co(NH3)6]+3 is a Lewis acid as it accepts electrons from the Lewis base NH3 and is electron deficient
c) CO is electron rich and can donate a pair of electrons rather than accepting. Thus CO in Ni(CO)4 is a lewis base not Lewis acid.
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