Which of the following gives a buffer solution when equal volumes of the two solutions are mixed? (a) 0.10 M NH3 and 0.10 M HCl (b) 0.20 M NH3 and 0.10 M HCl (c) 0.10 M NH4Cl and 0.10 M NH3 (d) 0.20 M NH4Cl and 0.10 M NaOH

Video transcript

Hey everyone, we're asked to identify a mixture from the following solution pairs where equal volumes of the two solutions. One mixed together will lead to the formation of a buffer. Now, as we've learned a buffer is a solution of a weak acid plus its conjugate base. So we have to find out which solution has these two components. Starting with a. We have 0.13 molar hydrochloric acid with 0.15 molar of sodium hydroxide. Now in the solution we have a mixture of a strong acid plus a strong base. So this cannot be a buffer based on the definition we just stated. Next, looking at B, we have 0.13 molar of our sulfuric acid with 0.13 molar of our sodium carbonate first. Let's go ahead and write out our reaction equation. So we have our sulfuric acid and this is going to react with sodium carbonate. Now when these two react, we get sodium sulfate plus carbon dioxide plus our water. So as we can see right here, one mole of sulfuric acid reacts with one mole of sodium carbonate. And since the polarities and volumes of the two solutions are equal, the reaction will be complete at the end of the reaction and there will only be sodium sulfate in the solution. So this mixture is not a buffer as well. Next let's go ahead and look at sea. So for c we have 0.26 molar of our hydrogen cyanide. And this is going to react with 0.13 moller of our potassium hydroxide. So let's go ahead and write out our reaction equation. We have our hydrogen cyanide and this is going to react with potassium hydroxide. When these two react, we get our potassium cyanide plus our water. So since we have equal volumes, let's assume that we have one leader of each solution. Now we can simply consider our polarity as moles. So we have 0.26 moles of our hydrogen cyanide and 0.13 moles of our potassium hydroxide based on our psyche aama tree. 0.13 mole of hydrogen cyanide will react with potassium hydroxide and we will have 0.13 mol of our hydrogen cyanide and 0.13 mol of our potassium cyanide in the solution. So our hydrogen cyanide is going to be our weak acid and our potassium cyanide is going to be the conjugate base of our weak acid. So it looks like answer choice. C is going to be our buffer But let's go ahead and assess D as well for D. We have 0.10 moller of our ammonium chloride with 0.20 molar of our hydrochloric acid. For this we know that ammonium chloride is a weak acid due to the ammonium ion and we know the hydrochloric acid is a strong acid. So this is a mixture of a weak acid plus a strong acid. So this mixture is not a buffer. So our final answer here is going to be answer choice C. Now I hope that made sense and let us know if you have any questions.