What is the pH of 1M NaOH, 1M HCl solution, saliva before meal, saliva after meal and lemon juice? Give the pH with complete solutions.

pH is defined as the negative log of Hydrogen ion concentration.

pH = -log[H⁺]

a similar relation is there to express the OH^- ion concentration for bases. It is written as

pOH = -log[OH^-]

pH and pOH are related by the following expression

pH + pOH = 14

The pH of 1M HCl would therefore be 

 = - log [H⁺]

 = - log [1] = 0

Therefore pH of 1 M HCl solution is 0. Similarly pOH of 1M HCl will be 

 = -log[OH^-]

 = - log [1] = 0

Hence the pH of 1M NaOH will be 

 = 14 - pOH

 = 14 - 0 = 14

The pH of saliva is 6.8. By how much this pH value will change depends upon the kind of meal taken by the person. If a meal is taken which has more acidic content, then pH of saliva will drop. On the other hand, if a meal which has more basic content is taken, the pH will increase. Citric acid is a weak organic acid, hence its pH will be close to 6.