Describe the properties of bases. Name two bases and their uses.

When a few drops of purple cabbage juice are added to a salt solution, it turns green. What is the nature of the acid and base from which this salt was formed?

You are given two beakers. One has $20 \mathrm{mL}$ of sodium hydroxide, which is a strong base, and the other has $20 \mathrm{mL}$ of ammonium hydroxide, which is a weak base. Both bases have the same concentration. Given an acid and an indicator, how can you tell the strong base from the weak base?