1 / 17

Understanding Bases and Alkalis: Key Properties and Reactions

Learn about bases, alkalis, and their reactions with acids, including properties, chemical reactions, and practical applications. Discover the distinctions between strong and weak alkalis and their common uses.

odessa
Télécharger la présentation

Understanding Bases and Alkalis: Key Properties and Reactions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Acids and Bases (3)

  2. Bases and Alkalis • Bases are the oxides or hydroxides of metals. • Contains either oxide ions (O2-) or hydroxide ions (OH-) Na+ ; O2- Zn2+ ; O2- Cu2+ ; O2- Mg2+ ; OH- Al3+ ; OH-

  3. The Definition of a Base An base is a substance that reacts with an acid to give a salt and water only. Base + Acid  Salt + Water

  4. Alkalis: Special Class of Bases • Soluble bases are called alkalis. • All alkalis are bases, but not all bases are alkalis. • Most bases are insoluble in water.

  5. Laboratory Alkalis • Sodium hydroxide, NaOH • Aqueous ammonia, NH3 • Calcium hydroxide, Ca(OH)2

  6. The Definition of an Alkali An alkali is a substance that produces hydroxide ions, OH- (aq) in water.

  7. Properties of Alkalis • Bitter taste and soapy feel. • Hazardous • Concentrated solutions: Corrosive & burn skin (Caustic) • Dilute solutions: Irritants • Acids change the colour of indicators. • Acids turn red litmus blue – a simple test for alkali.

  8. Chemical Reactions of Alkalis (1) • Alkalis react with acids to form a salt and water only. • Neutralisation reaction: The hydrogen ions (from the acid) and the hydroxide ions (from the alkali) react to form water.

  9. Chemical Reactions of Alkalis (1) For example, +  + +  + The ionic equation for any neutralisation reaction: H+ (aq) + OH- (aq)  H2O (l) Sodium hydroxide Hydrochloric acid Sodium chloride Water Sodium hydroxide Sodium sulfate Sulfuric acid Water

  10. Manganese (II) oxide Hydrochloric acid Manganese (II) chloride + + Water Manganese (IV) oxide Hydrochloric acid Manganese (II) chloride + + + Water Chlorine Which one is not a neutralisation reaction? • Reaction (1) • Reaction (2) MnO (s) + 2HCl (aq)  MnCl2 (aq) + H2O (l) MnO2 (s) + 4HCl (aq)  MnCl2 (aq) + 2H2O (l) + Cl2 (g)

  11. Moist red litmus paper turns blue Chemical Reactions of Alkalis (2) • Alkalis heated with ammonium salts give off ammonia gas. Alkali + Ammonium salt  Ammonia + Water + Salt Ammonia gas is recognized by its characteristic pungent smell.

  12. Chemical Reactions of Alkalis (3) • Alkalis react with solutions of metal ions • Precipitation reaction: Used as a test to identify metal ions in metal salts

  13. water water Strong Alkalis When strong alkalis are added to water, they become OH-(aq) ions in solutions. E.g. NaOH(s) Na+(aq) + OH-(aq) KOH(s) K+(aq) + OH-(aq)

  14. Weak Alkalis When weak alkalis are added to water, only a small fraction of the molecules form OH-(aq) ions. Most of the molecules remain unchanged. E.g. NH3 (g) + H2O (l) NH4+ (aq) + OH- (aq)

  15. Uses of Alkalis • Alkalis, like acids, are common in our daily lives. • To neutralise acids • Dissolve grease

  16. Uses of Bases and Alkalis • Ammonia solution: • In window cleaning solutions • In fertilisers • Magnesium hydroxide: • In toothpaste to neutralise acid on teeth • In antacids to relieve indigestion • Sodium hydroxide: • In making soaps and detergents • In industrial-cleaning detergents • Calcium oxide: • In neutralising acidic soil • To make iron, concrete and cement

  17. So, what have you learnt?

More Related