Question

Which of the following mixtures, when dissolved in 1.0 L of water, would function as a buffer?

0.10 mol of sodium hydroxide (NaOH) and 0.10 mol of hydrochloric acid (HCl)

0.10 mol of ammonium chloride (NH4Cl) and 0.10 mol of ammonia (NH3)

0.10 mol of ammonium chloride (NH4Cl) and 0.10 mol of ammonium bromide (NH4Br)

0.10 mol of sodium chloride (NaCl) and 0.10 mol of ammonium chloride (NH4Cl)

more than one of the above would be suitable buffers

Answer 1

A buffer solution is a mixture of weak acid and its conjugate base or a mixture of weak base and its conjugate base. We can identify a buffer when there is difference of one H+ between weak acid and its conjugate base or when there is difference of one OH- between weak base and its conjugate base.

• 0.10 mol of sodium hydroxide (NaOH) and 0.10 mol of hydrochloric acid (HCl), in this NaOH is a strong acid and HCl is a strong acid. So a neutralization reaction will occur thereofore this mixture will not act as buffer.
• 0.10 mol of ammonium chloride (NH4Cl) and 0.10 mol of ammonia (NH3), in this NH3 (NH4OH) is a weak base and NH4Cl(NH4+) is its conjugate base. This mixture will act as buffer.
• 0.10 mol of ammonium chloride (NH4Cl) and 0.10 mol of ammonium bromide (NH4Br), in these both NH4Cl and NH4Br are salts(of strong acid and weak base). This will not act as buffer.
• 0.10 mol of sodium chloride (NaCl) and 0.10 mol of ammonium chloride (NH4Cl), in this NaCl is a salt(of strong acid and strong base) and NH4Cl is also a salt(of strong acid and weak base). This will not act as buffer.

0.10 mol of ammonium chloride (NH4Cl) and 0.10 mol of ammonia (NH3) will acts as buffer.