Acids, Bases and Salts

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  • Acids are substances that can donate protons (H+ ions) to a solution.
  • They are characterized by a sour taste
  • the ability to turn blue litmus paper red. (ABR)
  • the ability to turn Methyl Orange into red.
  •  pH value less than 7.
  • Examples –  hydrochloric acid (HCl), sulfuric acid (H2SO4), acetic acid (CH3COOH), and citric acid (found in citrus fruits).

Arrhenius theory

  • proposed by Swedish chemist Svante Arrhenius in 1884.
    • According to Arrhenius, acids are substances that, when dissolved in water, release hydrogen ions (H+ ions) into the solution.
    • Arrhenius defined bases as substances that, when dissolved in water, release hydroxide ions (OH- ions) into the solution.

Brønsted-Lowry theory

  • formulated independently by Danish chemist Johannes Brønsted and British chemist Thomas Lowry in 1923.
    • According to the Brønsted-Lowry theory, an acid is defined as a substance that can donate a proton (H+ ion) to another substance.
    • A base, according to the Brønsted-Lowry theory, is defined as a substance that can accept a proton (H+ ion) from another substance.


  • Bases, also known as alkalis, are substances that can accept protons (H+ ions) from a solution.
  • They have a bitter taste, a slippery or soapy feel.
  • pH value greater than 7.
  • Bases turn red litmus paper blue.
  • the ability to turn Methyl Orange into Yellow.
  • the ability to turn Pheophthalin into Pink.
  • used for cleaning and neutralizing acids.
  • examples –  sodium hydroxide (NaOH), potassium hydroxide (KOH), and ammonia (NH3).


  • Salts are compounds formed when an acid reacts with a base through a chemical reaction called neutralization.
  • In a neutralization reaction, the H+ ions from the acid combine with the OH- ions from the base to form water (H2O), while the remaining ions combine to form a salt.
  • Salts can be composed of positively charged ions (cations) and negatively charged ions (anions). The cation comes from the base, and the anion comes from the acid.
  • Common table salt, sodium chloride (NaCl), is formed from the neutralization of hydrochloric acid (HCl) and sodium hydroxide (NaOH).

pH Scale:

  • The pH scale is a logarithmic scale used to measure the acidity or alkalinity (basicity) of a solution.
  • It ranges from 0 (strongly acidic) to 14 (strongly alkaline or basic), with 7 being neutral.
  • Solutions with a pH less than 7 are acidic, those with a pH greater than 7 are basic, and those with a pH of 7 are neutral (Rain Water).
  • The pH of a solution is determined by the concentration of H+ ions.
  • Higher H+ ion concentrations result in lower pH values (more acidic).
  • while lower H+ ion concentrations result in higher pH values (more basic).

Common Salt Types:

  • Sodium chloride (NaCl): Common table salt.
  • Calcium carbonate (CaCO3): Found in chalk, limestone, and antacids.
  • Sodium bicarbonate (NaHCO3): Baking soda, used in baking and as an antacid.
  • Magnesium sulfate (MgSO4): Epsom salt, used for muscle relaxation in baths.
  • Potassium nitrate (KNO3): Used in fertilizers and fireworks.

Alkali:  bases which are dissolved in water.

A buffer solution is a solution that can resist changes in its pH (acidity or alkalinity) when an acid or base is added to it.

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