Neutralization Chapter 21 Neutralization Reactions Neutralization Reaction A

Neutralization Chapter 21

Neutralization Reactions • Neutralization Reaction: A reaction between a strong acid and a strong base in an aqueous solution that produces a salt and water- a salt is an ionic compound These are double replacement reactions Used to produce pure salts HCl + KOH KCl + H 2 O The water is evaporated leaving behind the salt KCl

• Titrationsused to calculate the unknown concentration of an acid or base when you know the concentration of the other. • Standard solution of known concentration • End Pointthe point in the titration where the indicator changes color

• From a balanced equation, you can determine how many moles of a substance is needed to react with another substance to be neutralized: • EXAMPLE: How many moles of sulfuric acid are needed to neutralize 0. 5 mol of sodium hydroxide? H 2 SO 4 + 2 Na. OH Na 2 SO 4 + 2 H 2 O Using stoichiometry: 0. 5 mol Na. OH x 1 mol H 2 SO 4 2 mol Na. OH = 0. 25 mol H 2 SO 4 Do 1 & 2 page 616

• Stoichiometry can be used to determine the strength of an unknown acid or base: • Titrations: Steps: 1. A measured volume of unknown concentration acid or base is added to a flask 2. Several drops of the indicator is added to the solution 3. Measured volume of a base or acid of known concentration are mixed into the flask until the indicator just barely changes color

EXAMPLE: A 25 m. L solution of H 2 SO 4 is completely neutralized by 18 m. L of 1. 0 M Na. OH using phenolphthalein as an indicator. What is the concentration of the H 2 SO 4 solution? H 2 SO 4 + 2 Na. OH Na 2 SO 4 + 2 H 2 O 0. 018 L Na. OH x 1. 0 mol Na. OH x 1 mol H 2 SO 4 1 L Na. OH 2 mol Na. OH = 0. 009 mol H 2 SO 4 0. 025 L = 0. 36 M

• Equivalentsthe amount of acid or base that will give 1 mole of hydrogen or hydroxide Examples: HNO 3 H+ + NO 31 mole of HNO 3 gives 1 mole H+ 1 mole HNO 3 is 1 equivalent of HNO 3 H 2 SO 4 2 H+ + SO 421 mole of H 2 SO 4 is 2 equivalents of H 2 SO 4

• Gram Equivalent Massthe mass of one equivalent of a substance Molar Mass = gram equiv. mass # equiv/mol Example: HCl = 36. 5/1 equiv/mol = 36. 5 g/equiv H 2 SO 4 = 98 g/mol/2 equiv/mol = 49 g/equiv

• Normalityconcentration of a solution expressed as the number of equivalents of solute in 1 liter of solution N = equiv / L Equivalence pointthe point of neutralization in a titration The number of equivalents of acid and base are equal at this point so: NA x V A = N B x V B