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Acids & Bases
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Acids & Bases

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Acids & Bases Presentation Transcript

  • 1. ACIDS & BASES
  • 2. ACIDS
    • You can identify an acid from its name or chemical formula
    • Usually the name of an acid ends with the word “ acid ”
  • 3.
    • If you are given the chemical formula of a substance, you know it is an acid if:
      • the chemical formula starts with “ H ”
      • OR
      • the chemical formula ends with “ COOH ” ( carboxyl group )
    ACIDS
  • 4.
    • For example:
      • HF (aq) is an acid because it starts with H
        • Hydrofluoric acid is used for etching glass
      • CH 3 COOH (aq) is an acid because it ends with COOH
        • The name of this acid is “ acetic acid ”
        • Diluted acetic acid is vinegar
    ACIDS
  • 5. NAMING ACIDS
    • When the chemical formula of an acid starts with H and only contains one other non-metallic element, it is named as follows:
  • 6.
    • Step 1:
    • Start with the prefix “ hydro ”
    • Step 2:
    • take the first part of the non-metallic element and add the suffix “ ic ” and the word “ acid ”
    • ex.) HCl(aq) = “ hydrochloric acid ”
    • HF(aq) = “ hydrofluoric acid ”
    NAMING ACIDS
  • 7.
    • Sometimes the chemical formula of an acid contains a polyatomic ion
    • For example, H 2 SO 4 (aq) contains the polyatomic ion sulphate ( SO 4 2- )
    • When naming an acid containing a polyatomic ion, do the following:
    NAMING ACIDS
  • 8.
    • Step 1:
    • Start with the name of the element in the polyatomic ion that is not oxygen
    • Step 2:
    • Add the suffix “ ic ” and the word “ acid ”
    • ex.) H 2 SO 4 (aq) = sulphuric acid
    • H 3 PO 4 (aq) = phosphoric acid
    NAMING ACIDS
  • 9. BASES
    • Bases can also be identified from their name or chemical formula
    • A substance is a base if its name begins with the name of a metallic ion and ends with the word “ hydroxide ”
  • 10.
    • A substance is also a base if:
      • the chemical formula starts with a metallic ion or with the ammonium ion NH 4 +
      • AND
      • the chemical formula ends with OH ( hydroxyl group)
    BASES
  • 11.
    • For example, NaOH (s) starts with the metallic ion sodium ( Na + ) and ends with OH -
    • Similarly, KOH (s) starts with the metallic ion potassium ( K + ) and ends with OH -
    • NH 4 OH starts with the ammonium ion NH 4 + and ends with OH -
    BASES
  • 12. NAMING BASES
    • Step 1:
    • write the name of the positively charged ion
    • Step 2 :
    • Add the word “ hydroxide ”
    • ex.) KOH = potassium hydroxide
    • NH 4 OH = ammonium hydroxide
  • 13. ACIDS & BASES
    • Thousands of years ago, scientists used taste to distinguish acids from bases
    • Acids taste sour and bases taste bitter
    • Tasting unknown substances is not a safe way of identifying it or its properties
  • 14. pH
    • Today you can determine if a substance is an acid or a base by measuring its pH
    • The pH measurement is related to the number of hydrogen ions ( H + ) that are in a solution
    • The abbreviation “pH” stands for “ power of hydrogen ”
  • 15.
    • The pH scale is a number scale that indicates how acidic or basic a solution is
    • The pH of a substance can only be determined when it is in aqueous solution (dissolved in water )
    pH
  • 16.
    • Pure water has a pH of 7
    • Any substance with a pH of 7 when it is in aqueous solution is neutral
    • A neutral substance is neither an acid nor a base
    pH
  • 17.
    • An acid is a substance that has a pH of less than 7 when it is in aqueous solution
    • The more acidic a substance is, the lower the pH
    pH
  • 18.
    • A base is a substance that has a pH greater than 7 when it is in aqueous solution
    • The more basic a substance is, the higher the pH
    pH
  • 19. pH
  • 20.
    • One unit of change on the pH scale represents a change by a factor of 10 in how acidic or basic a solution is
    • ex.) stomach acid has a pH of 1 . This is 10 times more acidic than lemon juice, which has a pH of 2 .
    pH
  • 21. Acid-Base Indicators
    • An acid-base indicator is any substance that changes colour in the presence of an acid or a base
    • The most widely known acid-base indicator is litmus
  • 22.
    • Litmus is a plant extract that can be blue or red (pink)
    • Litmus turns red/pink in an acidic solution
    • Litmus turns blue in a basic solution
    Acid-Base Indicators
  • 23. The colour of hydrangea flowers is dependent upon the pH of the soil Acid-Base Indicators
  • 24.
    • It would be impossible to determine the pH of all solutions using just one indicator, such as litmus
    • Several other acid-base indicators exist, each producing a colour change at a specific pH level
    Acid-Base Indicators
  • 25.  
  • 26.
    • A universal indicator is a mixture of chemicals that changes colour through a wide range of pH values
    Acid-Base Indicators
  • 27.
    • An even more precise way of determining pH is to use a pH meter
  • 28. Properties of Acids & Bases
    • Similarities :
    • dissolve in water
    • conduct electricity in aqueous solution
    • can irritate or burn skin
  • 29.
    • Differences :
    BASES ACIDS turn litmus blue turn litmus red/pink do not react with metals to produce a compound and hydrogen gas react with metals to produce a compound and hydrogen gas do not corrode metals corrode metals release hydroxide ( OH - ) ions in aqueous solution release hydrogen ( H + ) ions in aqueous solution pH > 7 pH < 7 feel slippery do not feel slippery taste bitter taste sour
  • 30. Neutralization Reactions
    • Neutralization is a chemical reaction between an acid and a base that produces water (H 2 O) and a salt
    • acid + base  salt + water
  • 31.
    • The salts formed may be soluble in water or can be insoluble
    • If the salt is insoluble, a precipitate will form
    • Recall: a precipitate is a suspension of small, solid particles formed during a chemical reaction
    Neutralization Reactions
  • 32.
    • Applications of neutralization reactions:
    • Pharmaceuticals
    • Agriculture
    • Food industry
    Neutralization Reactions