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Chemistry 121/122

Chemistry 121/122. Acids, Bases and Salts. Properties of Acids. Acids, in foods, give a sour or tart taste Aqueous solutions of acids are electrolytes (conduct electricity (release ions in solution) Acids can be either strong or weak electrolytes May cause indicators to change colour

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Chemistry 121/122

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  1. Chemistry 121/122 Acids, Bases and Salts

  2. Properties of Acids • Acids, in foods, give a sour or tart taste • Aqueous solutions of acids are electrolytes (conduct electricity (release ions in solution) • Acids can be either strong or weak electrolytes • May cause indicators to change colour • Acids can react with metals to produce hydrogen gas (H2) • Acids can react with bases to form water and a salt • Acids can also react with hydrogen carbonates to produce carbon dioxide, water and a salt

  3. Properties of Bases • Most of the time, we do not eat anything basic - they are too bitter (soap) • They can be compared to acids by their properties • They are electrolytes that can change the colour of an indicator • They feel slippery when wet • When a base that contains hydroxide reacts with an acid, water and a salt form

  4. Arrhenius Acids and Bases • Although not entirely comprehensive, Arrhenius was one of the first scientists to propose general rules for acids and bases • He proposed acids to be those substances that produced H+ in solution (dissolved in water) • Bases were substances that produced OH- ions in solution (dissolved in water)

  5. Arrhenius Acids • When one hydrogen ionizes in solution, the acid is said to be monoprotic (HCl) • Two hydrogen ions = diprotic (H2SO4) • Three H+ = triprotic (H3PO4) • We now know that not all acids release hydrogen ions in solution • Only hydrogen involved in strong polar bonds (large differences in electronegativities) with an anion will ionize

  6. Difference between strong and weak bonds A strong acid (HCl) ionizes completely– HCl(aq) → H+(aq) + Cl-(aq) EN difference = 1.0 Even though a substance contains hydrogen, it may not be considered an acid if it does not ionize due to weak covalent bonds – CH4(g) = EN difference = 0.3

  7. Arrhenius Bases • Group 1 metals react with water to produce solutions that are basic Ex. Na + H2O → NaOH + H2 • the sodium hydroxide produced is basic • it is very soluble in water • as a result, in solution, it dissociates to form Na+ and OH- • There are strong bases and weak bases due to differences in solubility

  8. Practice 1. Write balanced equations for the reactions between the following: • Aluminum and sulfuric acid • Caclium carbonate and hydrobromic acid (metal carbonates produce water and carbon dioxide as products) 2. Write the net ionic equation for the reaction in question 1. (b)

  9. Bronsted-Lowry Acids and Bases • The definition of an Arrhenius acid and base does not include all acids and bases • Bronsted-Lowry attempts to be more comprehensive • Acids are defined as a H+ donor and bases are H+ acceptors • Ex. Ammonia (NH3) accepts a H+ to form ammonium (NH4+), so is a base

  10. Conjugate Acids and Bases • The particle formed by accepting the H+is called the conjugate acid • Conversely, the particle that remains once the acid has donated a H+ is called the conjugate base • Ex. NH3 + H2O → NH4+ + OH- • NH3 = base (accepts H+), H2O = acid (donates H+), NH4+ = conjugate acid (gains H+), OH- = conjugate base (loses H+). • Together, a conjugate acid-base pair forms – two substances linked by a single H+

  11. Hydronium Ion (H3O+) • When water gains a hydrogen ion, it becomes positively charged H2SO4 + H2O → H3O+ + HSO4- • However, water does not always do this… • Sometimes, it acts as an acid, donating H+ instead of gaining

  12. Practice • 1. Identify the conjugate acid-base pairs in each reaction. a. NH4+(aq) + OH-(aq) ↔ NH3(aq) + H2O(l) b. HBr(aq) + H2O(l) ↔ H3O+(aq) + Br-(aq) c. CO32-(aq) + H2O(l) ↔ HCO-(aq) + OH-(aq) 2. The products of an acid-base reaction are H3O+ and SO42-. Write a balanced equation for the reaction and identify the conjugate acid-base pairs.

  13. Lewis Acids and Bases • As an extension of his theory using electron dot diagrams, Lewis proposed that acids are electron pair acceptors and bases were electron pair donors • Such electrons are used to create covalent bonds between two atoms • H+ can accept electron pairs so it can be classified as a Lewis acid

  14. For the remainder of class… • Identify each reactant as an acid or base. Which definition should you use to help with your classification? • KOH + HBr → KBr + H2O • HCl + H2O → H3O+ + Cl- • Q. 1-8, p. 593 • Guided Reading for section 19.1

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