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UNIT 5 Aqueous Reactions and Solution Stoichiometry Acid-Base Neutralization.

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Presentation on theme: "UNIT 5 Aqueous Reactions and Solution Stoichiometry Acid-Base Neutralization."— Presentation transcript:

1 UNIT 5 Aqueous Reactions and Solution Stoichiometry Acid-Base Neutralization

2 Writing Equations for Reactions Involving Ions There are three ways to write equations for reactions involving ions. Molecular equation: HCl (aq) + AgNO 3 (aq)  AgCl (s) + HNO 3 (aq) Here no ions are shown but all reactants and products are identified and their physical states given. Complete or Total Ionic Equation: H + (aq) + Cl - (aq) + Ag + (aq) + NO 3 - (aq)  AgCl (s) + H + (aq) + NO 3 - (aq) Here ALL ions that exist in significant amounts in solution are shown. Spectator ions do not participate in the reaction but are shown. Net ionic equation: Cl - (aq) + Ag + (aq)  AgCl (s) Here only ions which participate in the reaction are shown. Spectator ions are NOT shown.

3 Writing Equations for Reactions Involving Ions Write the three equations for the reaction between solutions of barium nitrate and sodium phosphate. Molecular equation: 2Na 3 PO 4 (aq) + 3Ba(NO 3 ) 2 (aq)  Ba 3 (PO 4 ) 2 (s) + 6NaNO 3 (aq) Complete or Total Ionic Equation: 6Na + (aq) + 2PO 4 3- (aq) + 3Ba 2+ (aq) + 6NO 3 - (aq)  Ba 3 (PO 4 ) 2 (s) + 6Na + (aq) + 6NO 3 - (aq) Net ionic equation: 2PO 4 3- (aq) + 3Ba 2+ (aq)  Ba 3 (PO 4 ) 2 (s) The net ionic equation says that ANY soluble compound with phosphate and ANY soluble compound with barium ion will react to form the barium phosphate precipitate.

4 Acid-Base Neutralization Metathesis reactions are reactions of the form: AX + BY  AY + BX If either of the POSSIBLE new compounds AY or BX is: insoluble in water (a precipitate) a weak electrolyte a gas then the metathesis reaction will occur. Acid-base neutralization is a metathesis reaction. The product of the neutralization is either a weak electrolyte (usually water) or a gas.

5 Acid-Base Neutralization Acid-base neutralization is a metathesis reaction between an acid and a base. HX + BOH  BX + HOH ( = H 2 O ) Definitions of acids and bases Acids produce H + in water (Arrhenius) are proton donors (proton = H + ) (Brønsted- Lowry) Bases produce OH - in water (Arrhenius) are proton acceptors (Brønsted-Lowry)

6 Acid-Base Neutralization Acid-base neutralization is a metathesis reaction between an acid and a base. HX + BOH  BX + H 2 O acid + base  water (a weak electrolyte) Acids are proton donors (proton = H + ). Bases are proton acceptors and are metal hydroxides, ammonia, the amines and alcohols: HCl + NH 3  NH Cl -  NH 4 Cl(s) acid + ammonia  salt

7 Acid-Base Neutralization In a neutralization, the acid and the base are reactants. Identify the acid and the base in the following reactions (hint: look for the H + ): CH 3 OH + HBr  CH 3 OH Br - CH 3 NH 2 + H 2 O  CH 3 NH OH - Here, the acids had the H at the left of the formula (HBr, HOH). (It is helpful to know the Lewis structures of ammonia and of water.)

8 Acid-Base Neutralization Identify the acid and the base in the following reactions: CH 3 CO 2 H + KOH  CH 3 CO 2 - K + + H 2 O CH 3 COOH + CH 3 Li  CH 3 CO 2 - Li + + CH 4 Organic acids (CO 2 H or COOH) have the acid H at the right of the formula. Here are two more: CH 3 OH + NaH  CH 3 O - Na + + H 2 C 4 H 9 Li + H 2 O  C 4 H 10 + LiOH (Li + and OH - )

9 Acid-Base Neutralization KNOW THE STRONG ACIDS: HCl, HBr, HI, HClO 3, HClO 4, HNO 3, H 2 SO 4 by name AND formula. These ionize completely in water. HCl(aq)  H + (aq) + Cl - (aq) KNOW THE STRONG BASES: LiOH, NaOH, KOH, RbOH, CsOH (these are Group 1A metal hydroxides), Ca(OH) 2, Sr(OH) 2, and Ba(OH) 2, by name AND formula. These ionize completely in water. Ba(OH) 2 (aq)  Ba 2+ (aq) + 2OH - (aq) 2HCl(aq) + Ba(OH) 2 (aq)  2H 2 O(l) + BaCl 2 (aq) NET IONIC REACTION BETWEEN A STRONG ACID AND A STRONG BASE: H + (aq) + OH - (aq)  H 2 O(l)

10 Acid-Base Neutralization - Examples Acetic acid is neutralized by a solution of potassium hydroxide: M.E.: HC 2 H 3 O 2 (aq) + KOH (aq)  KC 2 H 3 O 2 (aq) + H 2 O (l) Complete ionic equation: HC 2 H 3 O 2 (aq) + K + (aq) + OH - (aq)  K + (aq) + C 2 H 3 O 2 - (aq) + H 2 O (l) Net ionic equation: HC 2 H 3 O 2 (aq) + OH - (aq)  C 2 H 3 O 2 - (aq) + H 2 O(l)

11 Acid-Base Neutralization - Examples Solid magnesium hydroxide is neutralized by hydroiodic acid: M.E.: Mg(OH) 2 (s) + 2HI (aq)  MgI 2 (aq) + 2H 2 O (l) Complete ionic equation: Mg(OH) 2 (s) + 2H + (aq) + 2I - (aq)  Mg 2+ (aq) + 2I - (aq) + 2H 2 O (l) Net ionic equation: Mg(OH) 2 (s) + 2H + (aq)  Mg 2+ (aq) + 2H 2 O (l)

12 Acid-Base Neutralization with Gas Formation Hydrochloric acid reacts with a solution of sodium sulfide. One of the products is a gas. Molecular Equation: 2HCl (aq) + Na 2 S (aq)  2NaCl (aq) + H 2 S (g) acid base salt gas The sulfide ion acts as a proton acceptor and is therefore the base. Complete ionic equation: 2H + (aq) + 2Cl - (aq) + 2Na + (aq) + S 2- (aq)  2Cl - (aq) + 2Na + (aq) + H 2 S (g) Net ionic equation: 2H + (aq) + S 2- (aq)  H 2 S (g)

13 Acid-Base Neutralization Recognize the “gases in disguise:” H 2 SO 3, H 2 CO 3 and NH 4 OH. These compounds are unstable in water and decompose to form a gas and water. H 2 SO 3 (aq)  H 2 O (l) + SO 2 (g) H 2 CO 3 (aq)  H 2 O (l) + CO 2 (g) NH 4 OH (aq)  H 2 O (l) + NH 3 (g)

14 Acid-Base Neutralization Hydrochloric acid is neutralized by a solution of sodium sulfite. 2HCl (aq) + Na 2 SO 3 (aq)  2NaCl (aq) + H 2 SO 3 (aq) Molecular equation: 2HCl (aq) + Na 2 SO 3 (aq)  2NaCl (aq) + H 2 O (l) + SO 2 (g) The sulfite ion acts as a proton acceptor and is therefore the base. Complete ionic equation: 2H + (aq) + 2Cl - (aq) + 2Na + (aq) + SO 3 2- (aq)  2Cl - (aq) + 2Na + (aq) + H 2 O(l) + SO 2 (g) Net ionic equation: 2H + (aq) + SO 3 2- (aq)  H 2 O (l) + SO 2 (g)


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