19.4 Neutralization Reactions

Neutralization During a neutralization reaction, an acid and a base react to produce a salt and water. Salts are ionic compounds consisting of an anion from an acid and a cation from a base. HCl (aq) + NaOH (aq) → NaCl (aq) + H 2 O (l) H 2 SO 4(aq) + 2NaOH (aq) → Na 2 SO 4(aq) + 2H 2 O (l) 2HCl (aq) + Ca(OH) 2(aq) → CaCl 2(aq) + 2H 2 O (l)

Titration Titration is the process of determining the concentration of an unknown acid/base solution by using a known concentration of base/acid. The point at which neutralization occurs is the equivalence point. An end point for a titration is when the indicator changes color. Equivalence point and end point are different points.

A flask with a known volume of acids (and an indicator) is placed beneath a buret that is filled with a base of known concentration. The base is slowly added from the buret to the acid. A change in the color of the solution is the signal that neutralization has occurred. Titration Process

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Sample Problem 19.7 Finding the Moles Needed for Neutralization How many moles of sulfuric acid are required to neutralize 0.50 mol of sodium hydroxide? The equation for the reaction is: H 2 SO 4 (aq) + 2NaOH(aq) → Na 2 SO 4 (aq) + 2H 2 O.

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. KNOWN mol NaOH = 0.50 mol Analyze List the knowns and the unknown. 1 UNKNOWN mol H 2 SO 4 = ? mol To determine the number of moles of acid, you need to know the number of moles of base and the mole ratio of acid to base. Sample Problem 19.7

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Calculate Solve for the unknown. 2 Use the mole ratio of acid to base to determine the number of moles of acid. Sample Problem mol NaOH × 1 mol H 2 SO 4 2 mol NaOH = 0.25 mol H 2 SO 4

Sample Problem 19.8 Determining Concentration by Titration A 25-mL solution of H 2 SO 4 is neutralized by 18 mL of 1.0M NaOH. What is the concentration of the H 2 SO 4 solution? The equation for the reaction is: H 2 SO 4 (aq) + 2NaOH(aq) → Na 2 SO 4 (aq) + 2H 2 O(l).

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. KNOWNS [NaOH] = 1.0M V NaOH = 18 mL = L V H 2 SO 4 = 25 mL = L Analyze List the knowns and the unknown. 1 UNKNOWN [H 2 SO 4 ] = ?M The conversion steps are as follows: L NaOH → mol NaOH → mol H 2 SO 4 → M H 2 SO 4. Sample Problem 19.8

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Calculate Solve for the unknown. 2 Use the molarity to convert the volume of base to moles of base. Sample Problem L NaOH × 1.0 mol NaOH 1 L NaOH = mol NaOH

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Calculate Solve for the unknown. 2 Use the mole ratio to find the moles of acid. Sample Problem mol NaOH × 1.0 mol H 2 SO 4 2 mol NaOH = mol H 2 SO 4

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Calculate Solve for the unknown. 2 Calculate the molarity by dividing moles of acid by liters of solution. molarity = mol of solute L of solution mol L = = 0.36M H 2 SO 4 Sample Problem 19.8

Example 1.A 17.5 mL sample of HCl is neutralized by 12.5 mL of 2.0M NaOH. What is the concentration of [H + ] in the original HCl solution? ANSWER: 1.4M 2.A 35.0 mL solution of calcium hydroxide is neutralized with 75.3 mL of 0.10M HCl. What is the concentration of [OH - ] in the original solution? ANSWER: 0.11M