6-2: Ranking Salt Solutions by pH
In this assignment you will be asked to rank aqueous solutions of acids, bases, and salts in order of increasing pH. This is most easily done by first identifying the strong acids that have the lowest pH, the strong bases that have the highest pH, and the neutral solutions that have a pH near 7. The weak acids will have a pH between 1 and 6 and the weak bases between 8 and 14. The exact order of weak acids and weak bases is determined by comparing the ionization constants (Ka for the weak acids and Kb for the weak bases). After ranking the pH of these solutions, you will then test your predictions in the laboratory.
1. Arrange the following 0.1 M solutions in order of increasing pH and state why you placed each solution in that position: NaCH3COO, HCl, HCN, NaOH, NH3, NaCN, KNO3, H2SO4, NH4Cl, H2SO3,, NaHCO3, Na3PO4 and CH3COOH.
In order of increasing pH:
Here are my predictions:
ACIDS - H2SO4 – - HCL – - H2SO3 – Weak Acid; - CH3COOH – Weak Acid; - NH4Cl – Weak Acid; - HCN- Weak Acid;
NEUTRAL - KNO3 – This is neutral
BASES - NaCH3COO – This is a weak base; - NaHCO3 –Weak Base; - NaCN – Weak Base; - NH3 – Weak Base; - Na3PO4 - Weak Base; - NaOH -
Once you have predicted the nature of each salt solution, you will use Virtual ChemLab to confirm your prediction. Each solution must be approximately 0.1 M for your comparisons to be valid. Most of the solutions in the Stockroom are approximately 0.1 M already. Two solutions will need to be diluted and three solutions will need to be prepared from solid salts. One of these salt solutions is already prepared and on the lab bench ready for you to measure the pH.
2. Start Virtual ChemLab and select Ranking Salt