Acids & Bases

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Acids & Bases

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

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