2. Unit 11: Acids and Bases

3. Unit Overview…  We will learn about Acids and Bases, two important types of compounds in chemistry  Learn the distinct properties of Acids and Bases  Understand the pH scale, and how we can use indicators to detect pH in an Acid-Base solution  Examine important acid-base chemical reactions

4. Arrhenius’ Theory of Acids and Bases Arrhenius Acid  Any substance that dissolves in water to produce hydrogen ions (H + ) or Hydronium ions (H 3 O + )  Ex: Hydrochloric acid, HCl (a strong acid).  HCl (g)  H + (aq) + Cl - (aq)  H 2 O (l) + H + (aq)  H 3 O + (aq)  ACIDIC solutions are formed when an acid transfers a proton to water.

5. Hydronium Ion  When an H + ion interacts with the electrons of the oxygen in a water molecule, an H 3 O + ion called the hydronium ion is formed.

6. Arrhenius’ Theory of Acids and Bases Arrhenius Base  Any substance that dissolves in water to produce hydroxide ions (OH - )  Ex: Sodium Hydroxide, NaOH (a strong base) or Ammonia NH 3  NaOH (s)  Na + (aq) + OH - (aq)  NH 3 (l) + H 2 O (l)  NH 4 + (aq) + OH - (aq) *Important Note – most bases end in “OH” but if there is CARBON attached to the compound then it is NOT a base

7. Properties of Acids  They’re electrolytes – chemicals that break up into ions in water, so they conduct electricity in water ○ Strong acid: good conductor ○ Weak acid: poor conductor  Sour Taste  React with most metals to produce H 2 (g)  React with bases to form Water and salt  React with indicators to change color pH values are from 0 to 6 see Reference Table M for color changes

8. Properties of Bases  Also electrolytes  Bitter Taste  Feel slippery (like soap)  React with acids to form water and salt  React with indicators to change color  pH values are 8 to 14  See Reference Table M for color changes

9. Properties of Salts  Also electrolytes  Ionic Compounds – containing one metal ion (+) and one non-metal ion (-), or a polyatomic ion (except OH - )  Ex) NaCl, MgCl 2, or Ca 3 (PO 4 ) 2  React with indicators to change color  pH values are around 7 (neutral)  See Reference Table M for color changes

10. pH Scale  A scale, called the pH scale, has been developed to express the concentration of hydrogen ions [H + ] as a number from 0 to 14.  A pH of 0 is strongly acidic  A pH of 7 is neutral  A pH of 14 is strongly basic (High concentration of H + ) Equal Concentration of H + and OH - ions (High concentration of OH - )

11. pH Scale

12. Acid – Base Indicators  An indicator is a chemical that changes color when it gains or loses a “proton” (H + ions).  There are many indicators listed on Reference Table M, and the color changes associated with certain pH values are given. See Table M We can use multiple indicators to find the approximate pH of a substance

13. Table K and Table L  These two tables list the most common acids and bases you will see in this course.  Table K : The top 4 acids are strong acids The last 2 are weak acids.  Table L : The top 3 bases are strong bases The last 1 is a weak base. Table K Table L

14. Acidity vs. Alkalinity  Acidity – is a measure of the strength of an acid related to the concentration of H + ions.  Alkalinity – is a measure of the strength of a base related to the concentration of OH - ions  High Acidity = pH less than 7  High Alkalinity = pH more than 7

15. Strong Acids  Strong acids : ionize (dissolve) completely, which means if 100 molecules are placed in water all 100 will break up into ions  Good Conductors!  Examples: HCl  H + + Cl - H 2 SO 4  2H + + SO 4 -2

16. Weak Acids  Weak acids: ionize (dissolve) only slightly, If 100 molecules are placed in water then only a small percentage will break up into ions.  Bad Conductors…  Example: acetic acid “vinegar” CH 3 COOH  CH 3 COO - + H + * NOTE: if an organic compound ends in COOH it’s a weak acid!!!

17. Strong Bases  Strong bases: ionize completely  Good Conductors!  Example: Sodium Hydroxide NaOH  Na + +OH -

18. Weak Bases  Weak base : ionizes slightly (won’t dissolve completely in water)  Bad Conductors…  Example: ammonia NH 3 + H 2 O  NH 4 + + OH -

19. Naming Acids

20. Binary acids –two elements - H+ *  Hydrogen _____ ide  Hydrogen chloride  Hydrogen fluoride  Hydrogen sulfide  Hydrogen bromide  Hydro_____ic acid  Hydrochloric acid  Hydrofluoric acid  Hydrosulfuric acid  Hydrobromic acid hydrogen _____ ide  hydro_____ic acid - Previous Naming System- New Naming System

21. Ternary acids: H+ & polyatomic ion  Hydrogen _____ate  Hydrogen sulfate  Hydrogen chlorate  Hydrogen nitrate  Hydrogen phosphate  _________ic acid  Sulfuric acid  chloric acid  nitric acid  Phosphoric acid Hydrogen _____ate  _________ic acid - Previous Naming System- New Naming System

22. More Ternary Acids – “-ite Ions”  Hydrogen _____ite  Hydrogen nitrite  Hydrogen sulfite  Hydrogen chlorite  _______ous acid  Nitrous acid  Sulfurous acid  Chlorous acid Hydrogen _____ite  _______ous acid - New Naming System- Previous Naming System

23. Naming Bases No change in how we name these… Full name of the metal atom + Hydroxide Ca(OH) 2  Calcium Hydroxide Ex)

24. Acid and Base Reactions  You will need to be familiar with 2 types of reactions involving acids & bases.  1 st reactions between any acid and certain metals.  2 nd reactions combine acids & bases to produce salt and water ( neutralization ).

25. Acid-Metal Reactions  Most metals will corrode when exposed to certain acids.  When this happens H 2 gas is produced.  Example: Ni + 2HCl  NiCl 2 + H 2 or 2Al + 6HCl  2AlCl 3 + 3H 2  Only precious metals won’t corrode like copper, gold, and silver because they aren’t reactive (Low on Table J)

26. Neutralization Reaction  In a neutralization reaction an Acid will react with a Base to produce salt and water. 1. Word equation 2. Formula equation 3. Net ionic equation  A net ionic equation has only the ions that take part in the reaction. The ions that don’t change are removed, called spectator ions. Hydrochloric Acid + Sodium Hydroxide yields Water + Sodium Chloride HCl + NaOH  H 2 O + NaCl H + (aq) + OH - (aq)  H 2 O (l)

27. Try This One H 2 SO 4 + 2NaOH 2H 2 O + Na 2 SO 4 2H + + SO 4 -2 + 2Na + + 2OH - 2H 2 O + 2Na + + SO 4 -2 H + + OH - H2OH2O Sulfuric acid + sodium hydroxide yields water + sodium sulfate

28. Finding Concentration of H + in Acids  A 1.0 M HCl “monoprotic acid”  HCl  H + + Cl -  Produces 1 H + so the concentration of H + is 1.0 M  Written like this: [H + ] = 1.0 M  A 1.0 M H 2 SO 4 “diprotic acid”  H 2 SO 4  2H + + SO 4 -2  Produces 2 H + so the concentration of H + is 2 x 1.0 M  Written like this: [H + ] = 2.0 M

29. Finding Concentration of OH - in Bases  A 1.0 M KOH  KOH  K + + OH -  Produces 1 OH - so the concentration of OH - is 1.0 M.  Written like this: [OH - ] = 1.0 M  A 1.0 M Mg(OH) 2  Mg(OH) 2  Mg +2 + 2OH -  Produces 2 OH - so the concentration of OH - is 2(1.0 M).  [OH - ] = 2.0 M

30. Titration  An Acid-Base titration is a technique used find the concentration of an acid or a base by neutralizing it.  During a titration you add set volumes of a base to an acid until it is neutralized.  Using the Acid-Base titration formula listed on Table T you can solve for your unknown concentration.

31. Acid- Base Titrations M a V a = M b V b (Table T) M a = molarity of H + V a = volume of acid M b = molarity of OH - V b = volume of base

32. Titrations (Neutralization) Problems  Ex. What volume of 0.50M HCl is required to neutralize 100mL of 2.0M NaOH? M a V a = M b V b M a = 0.5 M V a = ??? mL M b = 2.0 M V b = 100 mL 0.5(x) = 2.0(100) X = 400mL HCl

33. Bronsted-Lowry Acid-Base Theory Acids : chemicals that act as proton donors in water ( H + + H 2 O  H 3 O + ) Bases : Chemicals that act as proton acceptors in water (H 2 O  H + + OH - ) Water : Can act as an acid or a base because it can either donate or accept “protons” depending on the situation

34. Bronsted-Lowry Conjugate Acids/Bases  A conjugate acid - what is left of a Bronsted-Lowry Base after accepting a proton  A conjugate base - what is left of aa Bronsted-Lowry Acid after donating a proton  Ex)