Problem 19 - Chemistry An Atoms First Approach

Question

A certain buffer is made by dissolving \(\mathrm{NaHCO}_{3}\) and \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) in some water. Write equations to show how this buffer neutralizes added \(\mathrm{H}^{+}\) and \(\mathrm{OH}^{-}\).

Step-by-Step Solution

Answer

The buffer made by dissolving NaHCO3 and Na2CO3 in water neutralizes added H+ and OH- ions through the following reactions: 1. Reaction of bicarbonate ion (HCO3-) with H+ ions: \( HCO_3^-(aq) + H^+(aq) \rightarrow H_2CO_3(aq) \) 2. Reaction of carbonate ion (CO3^2-) with H+ ions: \( CO_3^{2-}(aq) + H^+(aq) \rightarrow HCO_3^-(aq) \) 3. Reaction of bicarbonate ion (HCO3-) with OH- ions: \( HCO_3^-(aq) + OH^-(aq) \rightarrow H_2O(l) + CO_3^{2-}(aq) \)

Step 1: Identify the buffer components when they are dissolved in water

When NaHCO3 and Na2CO3 are dissolved in water, they will dissociate and form their respective ions: 1. \( NaHCO_3(s) \rightarrow Na^+(aq) + HCO_3^-(aq) \) 2. \( Na_2CO_3(s) \rightarrow 2Na^+(aq) + CO_3^{2-}(aq) \)

Step 2: Write the equation for the reaction of bicarbonate ion with H+ ions

The bicarbonate ion (HCO3-) will react with the H+ ion, neutralizing it and forming carbonic acid (H2CO3). We can represent this reaction as follows: \( HCO_3^-(aq) + H^+(aq) \rightarrow H_2CO_3(aq) \)

Step 3: Write the equation for the reaction of carbonate ion with H+ ions

The carbonate ion (CO3^2-) will also react with the H+ ion, neutralizing it and forming bicarbonate ion (HCO3-). We can represent this reaction as follows: \( CO_3^{2-}(aq) + H^+(aq) \rightarrow HCO_3^-(aq) \)

Step 4: Write the equation for the reaction of bicarbonate ion with OH- ions

The bicarbonate ion (HCO3-) can also react with the added OH- ion. In this reaction, the bicarbonate ion (HCO3-) will donate a proton (H+) to the OH- ion, forming water (H2O) and the carbonate ion (CO3^2-). We can represent this reaction as follows: \( HCO_3^-(aq) + OH^-(aq) \rightarrow H_2O(l) + CO_3^{2-}(aq) \) With these four equations, we can now demonstrate how the given buffer consisting of NaHCO3 and Na2CO3 neutralizes added H+ and OH- ions through the reactions with bicarbonate and carbonate ions in the buffer system.