MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY
Adding acid to alkaline indigestion tablets. Image 2 of 2. Adding hydrochloric acid (HCl) to alkaline (pH greater than 7) indigestion tablets in solution with an indicator liquid. As the acid (pH less than 7) is added it begins to counter the alkalinity of the solution and reduce the pH. Here the solution has reached a neutral pH (pH7), shown by the indicator liquid changing 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 alkaline solution see image H460/0635.
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