MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY
Adding acid to alkaline indigestion tablets. Image 1 of 2. Adding hydrochloric acid (HCl) to alkaline (pH greater than 7) indigestion tablets in solution with an indicator liquid (green). As the acid (pH less than 7) is added it will begin to counter the alkalinity of the solution and reduce the pH. Eventually, when enough acid has been added, the solution will reach a neutral pH (pH7) and the indicator liquid will change colour to yellow. Indigestion tablets (antacids) are made from substances that form alkaline solutions in order to neutralise excess stomach acid that can cause indigestion (dyspepsia) and heartburn (pyrosis). For the solution at a neutral pH see image H460/0634.
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