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Inorganic chemistry Arrhenius theory of acids and bases. Arrhenius acids. Arrhenius bases. Assistance Lecturer Amjad Ahmed Jumaa www.soran.edu.iq 1 Acids and Bases: Savante Arrhenius (1884) proposed his concept of acids and bases. Arrhenius theory of acids and bases: Arrhenius acids: An acid is a substance that when dissolved in water, releases (H+), or (increase the concentration of hydronium ion, H3O+ (aq)). For example: HCl is an Arrhenius acid. www.soran.edu.iq HCl (aq) H+ (aq) + Cl-(aq). Arrhenius bases: A base is a substance when dissolved in water, release (OH-), ions, or (increase the concentration of hydroxide ion, OH(aq)). www.soran.edu.iq 3 www.soran.edu.iq 4 www.soran.edu.iq 5 2O NaOH(aq) H OH- (aq) + Na+(aq). Arrhenius acids: Were generally recognized as a substance that in aqueous solution, would: 1- Taste sour when diluted enough to be tasted. 2- Cause litmus paper to change from blue to red. 3- React with active metals such as magnesium, zinc, and iron to produce hydrogen gas, H2 (g): For example: Hydrochloric acid HCl (aq),(Arrhenius acid), react with magnesium metal to produce hydrogen gas and magnesium chloride: www.soran.edu.iq 2HCl (aq) + Mg(s) → H2 (g) + MgCl2 (aq). 4- React with bases (they contain hydroxide ion, OH-), to form water and compounds called salts. For example: hydrochloric acid, HCl (aq), react with potassium hydroxide, KOH (aq) as a base, to form water and potassium chloride (salt). HCl (aq) +KOH (aq) → Acid base H2O + KCl(aq). salt. Salts: is formed (is made up) of the cation from the base and the anion from the acid. The reaction of an acid with a base called neutralization. www.soran.edu.iq Neutralization: If the correct amounts of acids and bases are mixed together, the original properties of the acid and bases are lost. The reaction product has a taste that is salty sour or bitter. A salt and water were formed when an acid neutralizes a base. For example: H2SO4 (aq) + 2KOH (aq) → Acid base www.soran.edu.iq 2H2O (l) +K2SO4 (aq). salt. Arrhenius bases: (also called alkalies), were generally recognized by Arrhenius as that substance that in aqueous solution would: 1-Taste bitter (chemical used in the laboratory should never be tasted. 2- Feel slippery or soapy on the skin www.soran.edu.iq 9 3- Cause red litmus to change from red to blue. 4- React with acids to form water and salts. NaOH (aq) + HBr(aq) → H2O(l) + NaBr(aq). And thus: if you want to know wither a given compound, is an Arrhenius acid or base, just dissolve some of it in pure water and put a drop or two of the solution on blue litmus paper: If the litmus turns red, the compound is an acid, however if the solution turns red litmus to blue, the presence of a base compound is indicated. www.soran.edu.iq Many foods are acidic, cider vinegar contains acetic acid, lemons and other citrus fruits as well as many fruitflavored drinks contain citric acid. www.soran.edu.iq