What is the pH of stomach acid,
which is a solution of HCL with a hydronium concentration of 1.2 times 10 to the
minus three molar, to two significant figures?
The pH of a solution is an
indication of the concentration of H⁺ ions. H⁺ is otherwise known as a
hydronium ion. We’ve been told to model stomach
acid as a solution of hydrochloric acid, which is a strong acid. And the hydronium concentration
we’ve been given is 1.2 times 10 to the minus three molar or moles per decimeter
pH is defined as the negative
logarithm to the base 10 of the hydronium ion concentration, where the concentration
is expressed in molars. So the pH of stomach acid is equal
to the negative log of 1.2 times 10 to the minus three. Be careful not to use the natural
log, ln, in place of log to the base 10. This evaluates to 2.92 or as the
question asks 2.9, to two significant figures. This puts the pH of stomach acid
roughly between that of a lemon and an apple.