Video: Physical Chemistry, Inorganic Chemistry

What is the pH of stomach acid, which is a solution of HCl with a hydronium ion concentration of 1.2 × 10⁻³ M, to two significant figures?

01:31

Video Transcript

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 cubed.

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.

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.