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Chapter 5: Problem 73

Sodium hydroxide used to make standard \(\mathrm{NaOH}(\mathrm{aq})\) solutions for acid-base titrations is invariably contaminated with some sodium carbonate. (a) Explain why, except in the most precise work, the presence of this sodium carbonate generally does not seriously affect the results obtained, for example, when \(\mathrm{NaOH}(\mathrm{aq})\) is used to titrate HCl(aq). (b) Conversely, show that if \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) comprises more than \(1 \%\) to \(2 \%\) of the solute in NaOH(aq), the titration results are affected.

Short Answer

Expert verified
The presence of a small amount of Sodium Carbonate doesn't affect the titration results as sodium hydroxide, the strong base, reacts first with the acid. Sodium carbonate, being a weak base, only starts to react after all the sodium hydroxide has reacted. On the other hand, when sodium carbonate's composition goes beyond 1-2%, it starts reacting with the acid before all the sodium hydroxide is consumed, which leads to incorrect results.

Step by step solution

01

Explain why a small amount of sodium carbonate does not affect titration results

Sodium hydroxide is a strong base and sodium carbonate will act as a source of weak base. When a solution of sodium hydroxide is titrated against an acid (\(HCl\) in this case), the strong base will react first. Any sodium carbonate contamination will begin reacting only after all the sodium hydroxide has reacted. Therefore, even if there is a slight contamination of sodium carbonate, it will not significantly affect the results of the titration due to its weak basicity.
02

Show that if Na2CO3 is 1-2% of the solute in NaOH, titration results are affected

If the percentage of sodium carbonate rises to 1-2%, it means it is no longer negligible. The increased concentration of sodium carbonate can result in its reaction with the acid before all the sodium hydroxide is consumed. This would cause an earlier than expected end point in the titration, leading to higher values of acid concentration.

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Most popular questions from this chapter

Balance these equations for redox reactions occurring in acidic solution. (a) $\mathrm{MnO}_{4}^{-}+\mathrm{I}^{-} \longrightarrow \mathrm{Mn}^{2+}+\mathrm{I}_{2}(\mathrm{s})$ (b) $\mathrm{BrO}_{3}^{-}+\mathrm{N}_{2} \mathrm{H}_{4} \longrightarrow \mathrm{Br}^{-}+\mathrm{N}_{2}$ (c) $\mathrm{VO}_{4}^{3-}+\mathrm{Fe}^{2+} \longrightarrow \mathrm{VO}^{2+}+\mathrm{Fe}^{3+}$ (d) $\mathrm{UO}^{2+}+\mathrm{NO}_{3}^{-} \longrightarrow \mathrm{UO}_{2}^{2+}+\mathrm{NO}(\mathrm{g})$

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