Reactions  Another type of reaction occurs when an acid and a base (alkali) are mixed.  Acids – usually begin with a Hydrogen such as H 2 S or H(CO 3 )  Release hydrogen ions  Sour taste, form electrolytes in solution  React with metals to release hydrogen gas  Bases – usually have an Hydroxide ion such as Na(OH) or Ca(OH) 2  Release hydroxide ions  Bitter taste, feel slippery, form electrolytes in solution  Acids and Bases react to form a water and a salt – this is called neutralization

Stomach Acid  Heartburn is the result of excess stomach acid. Antacid tablets, which must be basic, act to neutralize the excess acid.  Stomach acid is primarily Hydrochloric Acid  One type of antacids is Magnesium Hydroxide  Write the chemical equation for the neutralization of stomach acid.

Other antacids  Calcium Carbonate is also an antacid.  Not all bases contain an hydroxide.  All bases like to take protons (hydrogen ions) so be careful when looking for neutralization reactions  You will always end up with a salt (a cation and an anion) and water

Neutralization Reactions  If you accidentally swallow lye (a caustic cleaning fluid), the first aid treatment is to give lemon juice (citric acid):  H 3 C 6 H 8 O 6 + NaOH  ____________ + __________  Give the name of the salt created  If you accidentally swallow toilet bowl cleaning (a strong acid), the first aid treatment is to give milk of magnesia  Mg(OH) 2 + HCl --> ____________ + __________  Give the name of the salt created

Neutralization Reactions  Write the neutralization reaction when:  H 3 PO 4 reacts with Al(OH) 3  HCl reacts with Ba(OH) 2  HC 2 H 3 O 2 reacts with KOH

Reduction-Oxidation Reactions  Redox reactions, or reduction-oxidation reactions, have a number of similarities to acid-base reactions.  Redox reactions are a family of reactions that are concerned with the transfer of electrons between molecules (species).  Like acid-base reactions, redox reactions are a matched set -- you don't have an oxidation reaction without a reduction reaction happening at the same time.

Oxidation and Reduction  Oxidation refers to the loss of electrons.  The oxidation number will INCREASE  Reduction refers to the gain of electrons.  The oxidation number will REDUCE or DECREASE  Each reaction by itself is called a "half-reaction", simply because we need two (2) half-reactions to form a whole reaction.  One half is the oxidation, the other half is the reduction.

Reducing and Oxidization Agents  We can also discuss the individual components of these reactions as follows.  If a chemical causes another substance to be oxidized, we call it the oxidizing agent.  In the equation above, Ag + is the oxidizing agent, because it causes Cu(s) to lose electrons.  If a chemical causes another substance to be reduced, we call it the reducing agent.  Cu(s) is the reducing agent in this case, as it causes Ag + to gain electrons.

Oxidation Practice  Determine the oxidation number of the elements in each of the following compounds: a. H 2 CO 3 b. N 2 c. Zn(OH) 4 2- d. NO 2 - e. LiH f. Fe 3 O 4

Oxidation and Reduction  For the equations – determine what is oxidized, what is reduced AND what is the reducing agent and what is the oxidizing agent.  a. 2Cr + + Sn 4+  Cr 3+ + Sn 2+  oxidized ___________________________  reduced ___________________________  b. 3 Hg Fe(s)  3 Hg 2 + 2Fe 3+  oxidized ___________________________  reduced ___________________________  c. 2As (s) + 3Cl 2 (g)  2 AsCl 3  oxidized ___________________________  reduced ___________________________

Oxidation and Reduction Would you use an oxidizing agent or reducing agent in order for the following reactions to occur?  a. ClO 3-  ClO 2 _________________________  b. SO 4 2-  S 2- _________________________  c. Mn 2+  MnO 2 _________________________  d. Zn  ZnCl 2 _________________________

Writing Half Reactions - Difficult!  When writing half-reactions, we usually show the electrons  Cu (s) ----> Cu e -  This half-reaction says that we have solid copper (with no charge) being oxidized (losing electrons) to form a copper ion with a plus 2 charge.  Ag + (aq) + e > Ag (s)  Here, a silver ion (silver with a positive charge) is being reduced through the addition of an electron to form solid silver.  The abbreviations "aq" and "s" mean aqueous and solid, respectively.

Example  Combine the two (2) half-reactions to form a redox equation:  Cu (s) ----> Cu e -  Ag + (aq) + e > Ag (s)  Balance the number of electrons on both halves of the equation, so multiply the silver by 2  Cu (s) ----> Cu e -  2Ag + (aq) + 2e > 2Ag (s)  Then add the two halves  Cu (s) + 2Ag + (aq) + 2e > Cu e - + 2Ag (s)  Then cancel out the electrons  Cu (s) + 2Ag + (aq) ----> Cu Ag (s)

Practice #1  Al (s) + O 2 (g)  Al 2 O 3  Al ½ Reaction:  ____Al ___ ( __)  ____Al ___ (___) + ___ e -1  O ½ reaction:  ____O 2 ___ ( __) + ___ e -1  ____O ___ (___)  Balance the electrons for both equations, then add them and cancel the electrons: