A solution contains 0.40 M NH3 and 0.20 M NH4Cl (pK_b = 4.74, pK_w = 14, log 2 = 0.301). Select the correct statements.

Adding a little HCl decreases the pH only slightly

Adding 0.1 mol NH4Cl per litre makes the pH exactly 9.26 (no volume change)

MolSynapse / Question bank / Ionic Equilibrium I / Buffer solutions and Henderson equation

JEE Advanced levelOne or more correct optionsDifficulty 3 of 3ie159

A solution contains 0.40 M $NH X_{3}$ and 0.20 M $NH X_{4} Cl$ ( $p K_{b} = 4.74$ , $p K_{w} = 14$ , $lo g 2 = 0.301$ ). Select the correct statements.

AIts pH is about 9.56
BIts pOH is greater than 4.74
CAdding a little HCl decreases the pH only slightly
DAdding 0.1 mol NH4Cl per litre makes the pH exactly 9.26 (no volume change)

Answer: A, C

pOH = 4.74 + log(0.2/0.4) = 4.439, pH = 9.56 (a true). pOH is smaller than 4.74 because salt < base (b false). Added HCl is absorbed by NH3 (c true). Adding 0.1 M salt gives ratio 0.3/0.4, pH = 9.38, not 9.26 (d false).

Practice Ionic Equilibrium I More on Buffer solutions and Henderson equation

Previous questionNext question

A solution contains 0.40 M NHX3​ and 0.20 M NHX4​Cl (pKb​=4.74, pKw​=14, log2=0.301). Select the correct statements.

Answer: A, C

More questions on Buffer solutions and Henderson equation

A solution contains 0.40 M $NH X_{3}$ and 0.20 M $NH X_{4} Cl$ ( $p K_{b} = 4.74$ , $p K_{w} = 14$ , $lo g 2 = 0.301$ ). Select the correct statements.