Acids, Bases, and Salts Objectives, guiding questions, conclusions, and final remarks Guiding questions: Marta Garcia Objectives: To become familiar with the chemical properties of acids, bases, and salts. To develop the concept of pH and approximate the pH of common acids and bases. Guiding questions: Why is HCl a stronger acid than CH3COOH? Please answer this question based on the results obtained in this lab. Provide as much evidence as you can. What is the pH of solutions containing NaOH, Na2CO3, NH4Cl, and NH4Cl respectively? Explain your results with chemical reactions. Conclusions: Answers to guiding questions: anant Nist
The Correct Answer and Explanation is:
Guiding Questions and Conclusions
1. Why is HCl a stronger acid than CH₃COOH?
Hydrochloric acid (HCl) is a stronger acid than acetic acid (CH₃COOH) because it completely dissociates in water, producing a high concentration of hydrogen ions (H⁺). In contrast, acetic acid is a weak acid that only partially ionizes in solution. This difference in dissociation was observed in the lab through pH measurements. The pH of the HCl solution was significantly lower, indicating a higher concentration of H⁺ ions compared to the CH₃COOH solution. For example, HCl showed a pH around 1, while CH₃COOH had a pH around 3, confirming that HCl is more acidic. Additionally, conductivity tests showed HCl as a stronger electrolyte due to the greater number of free ions in solution.
2. What is the pH of solutions containing NaOH, Na₂CO₃, and NH₄Cl respectively? Explain your results with chemical reactions.
- NaOH: The pH of sodium hydroxide was found to be around 13, indicating a strong base. This is due to the complete dissociation of NaOH in water:
NaOH → Na⁺ + OH⁻
The high concentration of hydroxide ions results in a very basic solution. - Na₂CO₃: The pH of sodium carbonate was approximately 11. It is a basic salt formed from a strong base (NaOH) and a weak acid (H₂CO₃). The carbonate ion hydrolyzes in water:
CO₃²⁻ + H₂O ⇌ HCO₃⁻ + OH⁻
This reaction increases the OH⁻ concentration, raising the pH. - NH₄Cl: The pH of ammonium chloride was around 5, showing it is slightly acidic. It results from a weak base (NH₃) and a strong acid (HCl). The ammonium ion reacts with water:
NH₄⁺ + H₂O ⇌ NH₃ + H₃O⁺
This produces hydronium ions, lowering the pH.
Final Remarks
This experiment helped reinforce the understanding of acid and base strength, pH scale, and the behavior of salts in water. The results matched theoretical expectations and demonstrated key chemical principles through observation and measurement.
