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According to their acidity, substances are classified into acidic, alkaline or neutral. Acidity is measured in pH, which stands for potential hydrogen. A neutral substance has a pH of 7.
Substances whose pH is less than 7, are acidic substances. The highest acidity level is pH 0. Acidity means that the concentration of positively charged hydrogen ions is higher than negatively charged hydroxyl ions (hydrogen and oxygen).
Acids are characterized by:
- Sour taste
- Redden the litmus paper
- Produce effervescence with calcium carbonate
- They react with some metals such as zinc or iron.
- They neutralize bases
- In aqueous solution they facilitate the passage of electric current
- They are corrosive to biological tissues such as skin
- Dissolve substances
Those whose pH is greater than 7, are alkaline substances. The highest alkalinity level is pH 14. Alkalinity means that the concentration of negatively charged hydroxyl ions (hydrogen and oxygen) is higher than positively charged hydrogen ions. Alkalines, also called bases, are characterized by:
- Bitter taste
- Tile litmus paper
- They are unctuous to the touch
- Substances that have been dissolved by acids precipitate
- In aqueous solution they also facilitate the passage of electric current
- Dissolve fats and sulfur
- They neutralize acids
Examples of neutral substances
- Milk: milk is a neutral substance (pH 6.5). However, when it comes into contact with gastric juices, it becomes an acidic substance, so, contrary to what is commonly believed, it is not recommended to consume it when suffering from heartburn.
- Running water: tap water or tap water must be a neutral substance. However, water can be ionized, meaning that its hydrogen ions (positively charged) can increase by becoming acidic.
- Mineral water with gas: Minerals and gas in bottled water do not change the pH of the water significantly.
- Mineral water without gas
- Liquid soap: the skin is an acidic environment (pH 5.5 approximately) while solid soaps have a pH greater than 8. Liquid soaps are synthetic products to which acidity is added to achieve a neutral pH. Glycerin soap is said to be "neutral" because it has a pH similar to that of skin, but chemically it is an acidic substance, since its pH is less than 7.
- Liquid laundry soap: neutral soap is less aggressive to fabrics than acid soaps.
- Blood: between 7.3 and 7.4
- Saliva: between 6.5 and 7.4
