Instruction: what happens when you blow air into alkaline water?

Response: When you blow air into alkaline water the C02 from your breath creates carbonic acid which lowers the potential hydrogen of the alkaline water.  If you blow air into the alkaline water long enough the alkaline water will eventually turn acidic.  Potential hydrogen drops can be used to measure the PH to show the effect of blowing air into alkaline water.  PH drops will show alkaline water as blue and purple, and they will show acidic water as yellow.