Explain how ranitidine (Zantac) reduces stomach acid production.

The pH is maintained in different fluids in the body by the use of buffers.

Calculate the pH of a buffer solution of 0.0200 mol dm^–3 carbonic acid, H₂CO₃, and 0.400 mol dm^–3 sodium hydrogen carbonate, NaHCO₃. The pK_a of carbonic acid is 6.35.

blocks/binds to H2/histamine receptors «in cells of stomach lining»

OR

prevents histamine binding to H2/histamine receptors «and triggering acid secretion»

prevents parietal cells from releasing/producing acid

Accept "H2-receptor antagonist/H2RA" OR "blocks/inhibits action of histamine" for M1.

ALTERNATIVE 1

pH = «pK_a + log \(\frac{{\left[ {{{\text{A}}^ - }} \right]}}{{\left[ {{\text{HA}}} \right]}}\) =» 6.35 + log (\(\frac{{0.400}}{{0.0200}}\))

«pH =» 7.65

ALTERNATIVE 2

K_a = 4.5 x 10^–7

«K_a = 0.400 x \(\frac{{\left[ {{{\text{H}}^ + }} \right]}}{{0.0200}}\), [H⁺] =» 2.3 x 10^–8 «mol dm^–3»

«pH =» 7.64

Award [2] for correct final answer.

Do not accept “pH = 8”.