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Acids and Bases

Acids and Bases. An Introduction Chapter 7. What do you already know about acids and bases?. What r some common acids?. Deoxyribonucleaic acid (DNA) Ribonucleaic acid (RNA) Amino acids (building blocks of protein)

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Acids and Bases

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  1. Acids and Bases An Introduction Chapter 7

  2. What do you already know about acids and bases?

  3. What r some common acids? • Deoxyribonucleaic acid (DNA) • Ribonucleaic acid (RNA) • Amino acids (building blocks of protein) • Lactic acid (build-up →sore muscles; by-product of cell metabolism and insufficient oxygen) • Boric acid (antiseptic) • Acetic acid ( in vinegar) • Citric acid (in fruits)

  4. What is an acid? • “an acid is a substance that produces hydrogen ions in solution” – Arrhenius 1884 • HCl (aq) → H+ (aq) + Cl- (aq)

  5. What r some common bases? • Most soaps/detergents • Most drain cleaners • Most window cleaners

  6. What is a base? • “ a substance that produces hydroxide ions in solution” – Arrhenius • NaOH (aq) →Na+ (aq) + OH- (aq)

  7. Distinguishing between acids and bases • Most solutions of both acids and bases are clear and colourless. • We need an indicator to tell them apart. • An indicator is a chemical which changes colour as the concentration of H+ (aq) and OH- (aq) changes. • Two common indicators are litmus and phenolpthalein

  8. Which compounds are acids and which are bases? • Acids: Formulas begin with one or more hydrogen atoms (ex. HCl (aq) or H2SO4 (aq)) • Names have the word “acid” in them (ex. Hydrochloric acid or sulfuric acid) • Bases: Formulas end with one or more “OH” (ex. NaOH (aq) or Ca(OH)2 (aq)) • Names end in hydroxide (ex. Sodium hydroxide or calcium hydroxide)

  9. Characteristics of acids • Sour taste (never taste lab chemicals) • Stinging feeling on mucous membranes • Strong acids will burn your skin • Aggressive reactions with metals • Conduct electricity • Turns blue litmus red • Phenolpthalein remains colourless • Forms carbon dioxide when reacting with carbonates and non metal oxides when reacting with water

  10. Characteristics of bases • taste bitter • feel slippery (soap and many drugs are bases) • caustic on organic matter • conduct electricity • Strong bases will burn your skin • Turn red litmus blue • Turns phenolpthalein pink • Does not react with carbonates but forms metallic oxides when reacting with water

  11. Oxides of Elements • Acids and bases are formed when oxides of elements react with water. • An oxide is a binary compound formed with an element and oxygen e.g. CO, CO2 , Al2O3, N2O5 • H2O (l) + CO2 (g) → H2CO3 (aq)

  12. pH : a “powerful” scale ( courtesy of Sørensen – a Danish biochemist) • Really means the power or concentration of hydrogen ions in solution • The lower the pH the greater the concentration of H+ (aq) and the more acidic the solution • The higher the pH, the greater the concentration of OH- (aq) and the more basic the solution • The scale goes from 0-14 with a midpoint of 7 • Solutions with a pH of 7 are neutral

  13. Ways to measure pH • pH paper • pH meters • pH probes

  14. How is pH calculated? • You need not know this but for future reference: • pH = -log [H+] • E.g. suppose that your concentration was 0.010 , enter this in your calculator and press the log button, change the sign, your answer should be 2.0 • Home work text p. 218 1-4, p. 225 1-5

  15. Properties of Acids and Bases • Two factors determine how many H+ ions are contained in a solution: concentration and percent ionization • Concentration refers to the amount of pure acid dissolved per litre of water • Percent ionization refers to the number of molecules that will ionize per 100 that dissolve. • Strong acids ionize completely whereas weak acids do not. E.g. sulfuric is strong and acetic is weak • Strong bases also ionize completely whereas weak bases do not e.g. NaOH is a strong base but NH3 is not

  16. Strong Acids and Bases

  17. Neutralization reactions • When an acid and a base react together to form a new compound, the word equation is • Acid + Base → Salt + Water • A salt is an ionic compound produced when an acid and base react • The reaction is also known as a neutralization reaction • HNO3 (aq) + KOH (aq) → KNO3 (aq)+ H20 (l)

  18. Chemistry of Swimming Pools • Acids, bases, and neutralization reactions help maintain water in swimming pools. • Water is chlorinated to kill bacteria and algae but chlorine gas is toxic so we use sodium hypochlorite instead • The following reactions describe how the pH of pools are adjusted • HOCl (aq) +NaOH (aq) → NaOCl (aq) + H2O (l) • NaOCl (aq) + H2O (l) →HOCl (aq) + Na+ (aq) + OH- (aq) • HOCl (aq) → H+ (aq) + OCl- (aq) • Acidic water may be neutralized by adding sodium carbonate • Basic water may be neutralized by adding hydrochloric acid

  19. Next up • Acid Rain • Purple Rain • Rain on Me

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