Chemistry unit 7 notes

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Chemistry unit 7 notes

  1. 1. Chemistry Unit 7 Acids and Bases
  2. 2. Acids <ul><li>An acid is a substance that produces positive hydrogen ions when placed in water. (H + ) </li></ul><ul><li>The strength of an acid depends on how completely the substance ionizes. Strong acids completely ionize in water. Weak acids ionize only slightly. </li></ul>
  3. 3. Base <ul><li>A base is a substance that produces negative hydroxide ions when placed in water. (OH - ) </li></ul><ul><li>The strength of a base depends on how completely the substance dissociates into metal ions and hydroxide ions in water. Strong bases dissociate completely. Weak bases do not. </li></ul>
  4. 4. Basic Acidic Neutral H+ H+ H+ OH- OH- OH- Solution Solution Solution Which solution is Acidic? Basic? Neutral???
  5. 5. Acids and Bases <ul><li>Produce H+ ions in water </li></ul><ul><li>Have a sour taste </li></ul><ul><li>Break down metals </li></ul><ul><li>Formula starts with H </li></ul><ul><li>Poisonous and corrosive to skin </li></ul><ul><li>pH less than 7 </li></ul><ul><li>Produce OH- ions in water </li></ul><ul><li>Have a bitter taste and a slippery feel </li></ul><ul><li>Break down fats and oils </li></ul><ul><li>Formula ends with OH </li></ul><ul><li>Poisonous and corrosive to skin </li></ul><ul><li>pH greater than 7 </li></ul>
  6. 6. Acids and Bases <ul><li>ACIDS </li></ul><ul><li>Examples: vinegar, lemon juice, aspirin, stomach acid, battery acid, cola, milk </li></ul><ul><li>BASES </li></ul><ul><li>Examples: soap, shampoo, ammonia, drain cleaner, antacids </li></ul>
  7. 7. Neutral Substances <ul><li>pH = 7 </li></ul><ul><li>Safe to ingest and leave on skin </li></ul><ul><li>Concentrations of H + ions and OH - ions are equal </li></ul><ul><li>Examples: dH2O, salts, most cosmetics, lotions, eye drops, etc. </li></ul>
  8. 8. Naming Acids (This should be review!) <ul><li>Every acid formula starts with H, a cation. To name an acid, look at the anion the hydrogen is bonded to. </li></ul><ul><li>H 2 S anion = chloride ion </li></ul><ul><li>H 2 SO 3 anion = sulfite ion </li></ul><ul><li>H 2 SO 4 anion = sulfate ion </li></ul>
  9. 9. Naming Acids <ul><li>If the name of the anion ends in –ide, the acid name begins with the prefix hydro- The stem of the anion is given then the suffix -ic is added and is followed by the word acid. </li></ul><ul><li> H 2 S </li></ul><ul><li>(anion sulfur)  hydro + stem + ic + acid </li></ul><ul><li> Hydrosulfuric Acid </li></ul>
  10. 10. Naming Acids <ul><li>If the name of the anion ends in –ite, the acid name is the stem of the anion with the suffix –ous and is followed by the word acid. </li></ul><ul><li> H 2 SO 3 </li></ul><ul><li>(anion Sulfite)  stem + ous + acid </li></ul><ul><li> Sulfurous Acid </li></ul>
  11. 11. Naming Acids <ul><li>If the name of the anion ends in –ate, the acid name is the stem of the anion with the suffix –ic and is followed by the word acid. </li></ul><ul><li>H 2 SO 4 </li></ul><ul><li>(anion Sulfate)  stem + ic + acid) </li></ul><ul><li>Sulfuric Acid </li></ul>
  12. 12. Does the formula contain Oxygen? Hydro “stem”ic acid Anion end in __ ? No Yes “ stem”ous acid “ stem”ic acid “ ate” “ ite” Naming Acids
  13. 13. Writing Formulas for Acids <ul><li>If the name starts with “hydro” </li></ul><ul><li>Hydrosulfuric Acid </li></ul><ul><li>Write the hydrogen ion with charge. </li></ul><ul><li>H +1 </li></ul><ul><li>Write the anion with the proper charge. </li></ul><ul><li>S -2 </li></ul><ul><li>Balance the charges using subscripts. </li></ul><ul><li> H 2 S </li></ul>
  14. 14. Writing Formulas for Acids <ul><li>If the name contains the suffix –ous </li></ul><ul><li>Sulfurous Acid </li></ul><ul><li>Write the hydrogen ion with charge. </li></ul><ul><li>H +1 </li></ul><ul><li>Look up the polyatomic ion (sulfite) and write it with the correct charge. </li></ul><ul><li>SO 3 -2 </li></ul><ul><li>Balance the charges using subscripts. </li></ul><ul><li> H 2 SO 3 </li></ul>
  15. 15. Writing Formulas for Acids <ul><li>If the name contains the suffix –ic without the prefix hydro </li></ul><ul><li>Sulfuric Acid </li></ul><ul><li>Write the hydrogen ion with charge. </li></ul><ul><li>H +1 </li></ul><ul><li>Look up the polyatomic ion (sulfate) and write it with the correct charge. </li></ul><ul><li>SO 4 -2 </li></ul><ul><li>Balance the charges using subscripts. </li></ul><ul><li>H 2 SO 4 </li></ul>
  16. 16. Writing Formulas/Naming Acids <ul><li>Remember the following statements… </li></ul><ul><li>“ I ate it and it was ic ky.” -ate becomes -ic </li></ul><ul><li>“ R ite ous ” -ite becomes -ous </li></ul><ul><li>(Righteous) </li></ul>
  17. 17. Naming Bases <ul><li>Bases are named using the traditional ionic naming system. </li></ul><ul><li>Metal name + polyatomic ion name </li></ul><ul><li>Examples: </li></ul><ul><li>Ca(OH) 2 = calcium hydroxide </li></ul><ul><li>NaOH = sodium hydroxide </li></ul><ul><li>Al(OH) 3 = aluminum hydroxide </li></ul>
  18. 18. Writing Base Formulas <ul><li>Base formulas are written using the traditional ionic system. </li></ul><ul><li>Look up the metal ion. Write the symbol with the proper charge. Ca +2 </li></ul><ul><li>Look up the polyatomic ion. With bases, this will always be hydroxide, OH -1 . </li></ul><ul><li>Balance the charges using subscripts. </li></ul><ul><li>Ca(OH) 2 </li></ul>
  19. 19. Neutralization Reactions <ul><li>When an acid is added to a base, the end products are always salt and water. (neutral) </li></ul><ul><li>A salt is defined as the neutral end product of an acid/base reaction. </li></ul><ul><li>ACID + BASE  SALT + WATER </li></ul><ul><li>H 2 S + Ca(OH) 2  CaS + H 2 O </li></ul><ul><li>What is wrong with this equation??? </li></ul>
  20. 20. Balance the final equation! <ul><li>H 2 S + Ca(OH) 2  CaS + H 2 O </li></ul><ul><li>1 Ca 1 </li></ul><ul><li>1 S 1 </li></ul><ul><li>4 H 2 </li></ul><ul><li>2 O 1 </li></ul><ul><li>H 2 S + Ca(OH) 2  CaS + 2 H 2 O </li></ul>
  21. 21. Neutralization Reactions <ul><li>Try another example: </li></ul><ul><li>Acid + Base  Salt + Water </li></ul><ul><li>H 2 SO 4 + NaOH  Na 2 SO 4 + H 2 O </li></ul><ul><li>1 Na 2 </li></ul><ul><li>1 SO 4 1 </li></ul><ul><li>3 H 2 </li></ul><ul><li>1 O 1 </li></ul><ul><li>H 2 SO 4 + 2 NaOH  Na 2 SO 4 + 2 H 2 O </li></ul>
  22. 22. Take it one step further… <ul><li>Sulfurous acid and sodium hydroxide yields sodium sulfite and water. </li></ul><ul><li>H 2 SO 3 + NaOH  Na 2 SO 3 + H 2 O </li></ul><ul><li>1 Na 2 </li></ul><ul><li>1 SO 3 1 </li></ul><ul><li>3 H 2 </li></ul><ul><li>1 O 1 </li></ul><ul><li>H 2 SO 3 + 2NaOH  Na 2 SO 3 + 2H 2 O </li></ul>
  23. 23. One Last Step <ul><li>Hydrosulfuric acid and calcium hydroxide yields what??? </li></ul><ul><li> H 2 S + Ca(OH) 2  </li></ul><ul><li>One product will always be water. </li></ul><ul><li>H 2 S + Ca(OH) 2  H 2 O + </li></ul><ul><li>The other product will be the + ion of the base bonded with the – ion of the acid. </li></ul><ul><li>H 2 S + Ca(OH) 2  2H 2 O + CaS </li></ul>
  24. 24. pH Scale <ul><li>pH – a number used to denote the hydrogen ion concentration, or acididty, of a solution </li></ul><ul><li>pH Scale Typically runs from 0 – 14 </li></ul><ul><li>0 7 14 </li></ul>Acidic Basic Neutral
  25. 25. pH Indicators <ul><li>A chemical substance that changes color in the presence of an acid and/or a base. </li></ul><ul><li>pH paper – Dip the paper, match color to scale on vial to determine numeric pH. </li></ul><ul><li>pH<7 = acid, pH>7 = base, pH = 7 neutral </li></ul><ul><li>2) Litmus – Dip one red and one blue paper. </li></ul><ul><li>Red stays red, blue turns red  Acid </li></ul><ul><li>Blue stays blue, red turns blue  Base </li></ul><ul><li>Red stays red, blue stays blue  Neutral </li></ul>
  26. 26. pH Indicators <ul><li>Bromthymol Blue – Add a few drops of bromthymol blue to the substance. </li></ul><ul><li>If the blue color turns to yellow  Acid </li></ul><ul><li>If the blue color stays blue  Base </li></ul><ul><li>Phenolphthalein – Add a few drops of phenolphthalein to the substance. </li></ul><ul><li>If the clear liquid turns to pink  Base </li></ul><ul><li>If the clear liquid remains clear  Acid </li></ul>
  27. 27. Concentration <ul><li>Strength of an acid or base is determined by the amount of ionization. Concentration is determined by the amount of water added to the substance. </li></ul><ul><li>Molarity (M) </li></ul><ul><ul><li>The number of moles of solute dissolved in each liter of solution. </li></ul></ul><ul><ul><li>Molarity = moles of solute </li></ul></ul><ul><ul><li> liters of solution </li></ul></ul>
  28. 28. Example Problem #1 <ul><li>If 1.00 liter of sugar water contains exactly 1.00 mole of sugar, what is its molarity? </li></ul><ul><ul><li>Molarity = 1.00 mol </li></ul></ul><ul><ul><li> 1.00 L </li></ul></ul><ul><ul><li>Molarity = 1.00 M </li></ul></ul>
  29. 29. Example Problem #2 <ul><li>If 1.00 liter of sugar water contains exactly 2.00 mole of sugar, what is its molarity? </li></ul><ul><ul><li>Molarity = 2.00 mol </li></ul></ul><ul><ul><li> 1.00 L </li></ul></ul><ul><ul><li>Molarity = 2.00 M or 2.00 mol/L </li></ul></ul><ul><ul><li>(Twice as concentrated…) </li></ul></ul>
  30. 30. Example Problem #3 <ul><li>What is the molarity when 0.75 mol is dissolved in 2.50 L of solution? </li></ul><ul><ul><li>Molarity = 0.75 mol = 0.30 mol/L or 0.30M </li></ul></ul><ul><ul><li> 2.50 L </li></ul></ul>
  31. 31. In Lab, grams are typically used in place of moles. <ul><li>If you wanted to make 2.00L of a 6M HCl solution, how much HCl would you need? </li></ul><ul><li>First, calculate the molar mass of the acid. </li></ul><ul><li>H 1 x 1.00795 = 1.00795 </li></ul><ul><li>Cl 1 x 35.453 = 35.453 </li></ul><ul><li> 36.46095 = 36.461 </li></ul>
  32. 32. If you wanted to make 2.00L of a 6M HCl solution, how much HCl would you need? <ul><li>First, calculate the molar mass of the acid. </li></ul><ul><li>HCl contains 36.461 g/mol </li></ul><ul><li>It would take 36.461 g of HCl to make 1 liter of a 1M HCl solution. How many grams would it take to make 2L of a 1M solution? </li></ul><ul><li>2 x 36.461g = 72.922g </li></ul>
  33. 33. If you wanted to make 2.00L of a 6M HCl solution, how much HCl would you need? <ul><li>It takes 72.922g of HCl to make 2 liters of a 1M solution. How much would it take to make 2 liters of a 6M solution? </li></ul><ul><li>6 x 72.922g = 437.532 g </li></ul>
  34. 34. Try One More <ul><li>Suppose you wanted to make 2 liters of a 0.5 M solution of HCl. How much HCl would you need? </li></ul><ul><li>Each mole of HCl is equal to 36.461g </li></ul><ul><li>For a 0.5 M solution, you would need half that much. 36.461 x 0.5 = 18.2305g. </li></ul><ul><li>However, you want to make 2 liters, so double that amount. 18.2305 x 2 = 36.461g. </li></ul>

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