© Copyright R.J. Rusay Aqueous Reactions Dr. Ron Rusay

© Copyright R.J. Rusay Aqueous Reactions  There are several general types: 1) Precipitation: An insoluble salt forms from the addition of solutions. (Refer to Solubility Rules) 2) Acid-Base Reactions (Neutralization) generally produces a salt plus water 3) Oxidation-Reduction (Redox) there is a change in oxidation numbers between reactants and products

© Copyright R.J. Rusay Solution Test Apparatus for Electrolytes

© Copyright R.J. Rusay Conductivity

Electrolytes  Aqueous solutions can be categorized into 3 types: non-electrolytes, strong electrolytes or weak electrolytes based on their ability to conduct electricity.  A solution must have ions to conduct.  Pure Water does not conduct.  Aqueous solutions can be tested for conductivity which will determine the degree of ionization of the solutes.  It is possible to have full or partial ionization.

© Copyright R.J. Rusay Electrolytes  Almost all ionic compounds and a few molecular compounds are strong electrolytes.  Several molecular compounds are weak conductors, most are non-conductors.  Conductivity is directly related to the amount of ionization, i.e. ions in solution. Table salt, sodium chloride, is completely ionized: NaCl (s) + H 2 O (l) ---> NaCl (aq) ---> 0.10MNa + (aq) + Cl - (aq) 0.00M 0.10M 0.10M Molarity (M) = Moles solute / Liter solution

© Copyright R.J. Rusay Electrolytes � Concentrations: � 2 2 � CaCl 2 (s) + H 2 O (l) ---> CaCl 2(aq) ---> 0.10MCa 2+ (aq) + 2 Cl - (aq) 0.00M 0.10M 0.20M Molarity (M) = Moles solute / Liter solution

© Copyright R.J. Rusay Electrolytes  Sugars like sucrose are non-ionic, molecular compounds that dissolve but produce no ions. C 12 H 22 O 11 (S) + H 2 O (l) ----> C 12 H 22 O 11 (aq)  Some molecular compounds like acetic acid ionize partially (dissociate) in water HC 2 H 3 O 2 (l) + H 2 O (l) H 3 O + (aq) M C 2 H 3 O 2 - (aq) M M Molarity (M) = Moles solute / Liter solution

© Copyright R.J. Rusay Aqueous Acids � Any compound that provides a proton can be considered an acid. Strong acids are sulfuric acid, nitric acid, perchloric acid, HI, HBr and HCl.

© Copyright R.J. Rusay Electrolytes � How would the conductivity of acetic acid compare to hydrochloric acid?

HCl Completely Ionized Acetic Acid (HC 2 H 3 O 2 )

© Copyright R.J. Rusay Aqueous Bases  Any compound that accepts a proton is a base.  The common bases are group IA & IIA metal hydroxide compounds. They are strong bases, dissociating completely in water.  An example of a weak base is ammonia. NH 3 (g) + H 2 O (l) NH 3 (aq) NH 4 + (aq) + OH - (aq)

An Aqueous Solution of Sodium Hydroxide NH 3 in Water

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© Copyright R.J. Rusay Aqueous Reactions: Neutralization

© Copyright R.J. Rusay Aqueous Reactions: Neutralization Net Ionic Equations HCl (aq) + NaOH (aq) ---> NaCl (aq) + H 2 O (l) ___________________________________________________ � � HCl (aq) ---> H + (aq) + Cl - (aq) � � NaOH (aq) ---> Na + (aq) + OH - (aq) � � NaCl (aq) ---> Na + (aq) + Cl - (aq) ________________________________________________ Na + (aq) + OH - (aq) + H + (aq) + Cl - (aq) ---> Na + (aq) + Cl - (aq) + H 2 O (l) _______________________________________________________ H + (aq) + OH - (aq) ---> H 2 O (l)

An aqueous solution of H 2 SO 4 is added to aqueous Ba(OH) 2. The reaction is monitored using a conductivity tester. Predict the correct statement(s). I) Both H 2 SO 4 and Ba(OH) 2 are strong electrolytes. II) This is a neutralization reaction. III) This is a precipitation reaction. IV) The light bulb will glow at the neutralization point. A) II B) I and II C) I, II and III D) I, II, III and IVQUESTION

An aqueous solution of H 2 SO 4 is added to aqueous Ba(OH) 2. The reaction is monitored using a conductivity tester. Predict the correct statement(s). I) Both H 2 SO 4 and Ba(OH) 2 are strong electrolytes. II) This is a neutralization reaction. III) This is a precipitation reaction. IV) The light bulb will glow at the neutralization point. A) II B) I and II C) I, II and III D) I, II, III and IVANSWER

© Copyright R.J. Rusay Aqueous Reactions: Acid-Base

QUESTION If an antacid contains Al(OH) 3 it will form AlCl 3 upon neutralization of stomach acid. How many moles of Cl – ions are in mL of M AlCl 3 ? A M B M C M D M Molarity (M) = Moles solute / Liter solution

ANSWER If an antacid contains Al(OH) 3 it will form AlCl 3 upon neutralization of stomach acid. How many moles of Cl – ions are in mL of M AlCl 3 ? A M B M C M D M AlCl 3 dissociates into 3 moles of Cl –. Molarity (M) = Moles solute / Liter solution

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Pb(NO 3 ) 2 (aq) + NaI (aq)  NaNO 3 (aq) + PbI 2 (s) How do you know the state of the products: (s) vs. (aq)? What type of reaction is it? Double Displacement & Precipitation Write a balanced equation for the reaction. 2 2

QUESTION Given the insoluble compound Al 2 (CO 3 ) 3 predict the ions and coefficients that would be necessary to complete the following net ionic equation: __ _____ + ____ _____  Al 2 (CO 3 ) 3 A.2 AlCl Na 2 CO 3 also include 6 NaCl on right B.3 Al CO 3 2– C.2 Al CO 3 2– D.2 Al 3+ 6 Cl – + 3 CO 3 2– + 6 Na +

ANSWER Given the insoluble compound Al 2 (CO 3 ) 3 predict the ions and coefficients that would be necessary to complete the following net ionic equation: __ _____ + ____ _____  Al 2 (CO 3 ) 3 A.2 AlCl Na 2 CO 3 also include 6 NaCl on right B.3 Al CO 3 2– C.2 Al CO 3 2– D.2 Al 3+ 6 Cl – + 3 CO 3 2– + 6 Na +

© Copyright R.J. Rusay Aqueous Reactions: Precipitation Net Ionic Equations  50mL of a 0.1M solution of sodium sulfate is mixed with 50mL of a 0.2M solution of silver nitrate. What is the result?  Molecular Equation: ?Na 2 SO 4(aq) + ?AgNO 3(aq) ---> ?Na 2 SO 4(aq) + ?AgNO 3(aq) ---> ?Ag 2 SO 4(s) + ?NaNO 3(aq)

© Copyright R.J. Rusay Aqueous Reactions: Precipitation Net Ionic Equations Na 2 SO 4(aq) + 2 AgNO 3(aq) -->Ag 2 SO 4(s) + 0.1M0.2M 2 NaNO 3(aq) Ionic Reaction (Reactants): Na 2 SO 4(aq)  2 Na + (aq) + SO 4 2- (aq) 2 AgNO 3(aq)  2 Ag + (aq) + 2 NO 3 1- (aq) 2 AgNO 3(aq)  2 Ag + (aq) + 2 NO 3 1- (aq) 2 Na + (aq) + SO 4 2- (aq) + 2 Ag + (aq) + 2 NO 3 1- (aq) 0.2M0.1M0.2M 0.2M 0.2M0.1M0.2M 0.2M

© Copyright R.J. Rusay Aqueous Reactions: Precipitation Net Ionic Equations Na 2 SO 4(aq) + 2 AgNO 3(aq) -->Ag 2 SO 4(s) + 0.1M0.2M 2 NaNO 3(aq) Ionic Reaction (Products): 2 NaNO 3(aq)  2 Na + (aq) + 2 NO 3 1- (aq) Ag 2 SO 4(s)  Does not dissolve (ionize) Ag 2 SO 4(s)  Does not dissolve (ionize) 2Na + (aq) + 2NO 3 1- (aq) + Ag 2 SO 4(s) 0.2M 0.2M solid 0.2M 0.2M solid

© Copyright R.J. Rusay Aqueous Reactions: Precipitation Net Ionic Equations Na 2 SO 4(aq) + 2 AgNO 3(aq) -->Ag 2 SO 4(s) + 2 NaNO 3(aq) Overall Ionic Reaction: 2Na + (aq) + SO 4 2- (aq) +2Ag + (aq) + 2NO 3 1- (aq)  2Na + (aq) + Ag 2 SO 4(s) + 2NO 3 1- (aq) Net Ionic Equation: (Subtract Spectator Ions) 2Ag + (aq) + SO 4 2- (aq)  Ag 2 SO 4(s) = M Na2SO4 xV Na2SO4 / 1:1 stoichiometry = 0.10M x L/ 1 = mol How many moles? M x V solution = mol

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Pb(NO 3 ) 2 (aq) + NaI (aq)  NaNO 3 (aq) + PbI 2 (s) Write a balanced Net Ionic equation for the reaction. 2 2 Pb 2+ ( aq) + 2 I 1- (aq)  PbI 2 (s) What are the spectator ions in the reaction? 2 Na 1+ ( aq) ; 2 NO 3 1- (aq)

QUESTION

ANSWER E)All of these are soluble in water. According to the solubility rules for ionic compounds, compounds containing Group IA ions or nitrate ions will always be soluble. Compounds containing halides are generally soluble, aside from silver, leadand mercury(I) halides.

QUESTION If you began a reaction with the following ions in solution (all would be written with an aq subscript) how would you represent the proper final net ionic equation? (Consult a solubility Table.) 6Na + + 2PO 4 3– + 3Fe NO 3 –  A.3Na + + PO 4 3– + Fe NO 3 –  No Reaction B.6Na + + 2PO 4 3– + 3Fe NO 3 –  Fe 3 (PO 4 ) 2 (s)+ 6NaNO 3 C.3Na + + PO 4 3– + Fe NO 3 –  Fe 3 (PO 4 ) 2 (s)+ 6 Na NO 3 – D.2PO 4 3– + 3Fe 2+  Fe 3 (PO 4 ) 2 (s)

If you began a reaction with the following ions in solution (all would be written with an aq subscript) how would you represent the proper final net ionic equation? (Consult a solubility Table.) 6Na + + 2PO 4 3– + 3Fe NO 3 –  A.3Na + + PO 4 3– + Fe NO 3 –  No Reaction B.6Na + + 2PO 4 3– + 3Fe NO 3 –  Fe 3 (PO 4 ) 2 (s)+ 6NaNO 3 C.3Na + + PO 4 3– + Fe NO 3 –  Fe 3 (PO 4 ) 2 (s)+ 6 Na NO 3 – D.2PO 4 3– + 3Fe 2+  Fe 3 (PO 4 ) 2 (s) ANSWER

© Copyright R.J. Rusay Oxidation-Reduction � Oxidation is the loss of electrons. � Reduction is the gain of electrons. � The reactions occur together. One does not occur without the other. � The terms are used relative to the change in the oxidation state or oxidation number of the reactant(s).

© Copyright R.J. Rusay Aqueous Reactions: Oxidation - Reduction � In the following reaction, identify what is being oxidized and what is being reduced. What is the total number of electrons involved in the process?

Oxidation Reduction Reactions

QUESTION In a redox reaction, oxidation and reduction must both occur. Which statement provides an accurate premise of redox chemistry? A.The substance that is oxidized must be the oxidizing agent. B.The substance that is oxidized must gain electrons. C.The substance that is oxidized must have a higher oxidation number afterwards. D.The substance that is oxidized must combine with oxygen.

ANSWER In a redox reaction, oxidation and reduction must both occur. Which statement provides an accurate premise of redox chemistry? A.The substance that is oxidized must be the oxidizing agent. B.The substance that is oxidized must gain electrons. C.The substance that is oxidized must have a higher oxidation number afterwards. D.The substance that is oxidized must combine with oxygen.

QUESTION

ANSWER 2 – 2 O 2 B)NO Oxygen almost always has an oxidation state of 2 when part of a compound. The exception is when it is part of a peroxide. For example, hydrogen peroxide H. Then it has an oxidation state of –1.