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19 SCH4U-C Acids, Bases, and Neutralization
December 16, 2015
Lesson 19 Chemistry SCH4U-C 1 Introduction Acids and bases react with one another in neutralization reactions, illustrated by the equation below: acid + base water + salt HA (aq) + BOH (aq) HOH (l) + BA (aq) The water is derived from the hydrogen ion of the acid and the hydroxide ion of the base. The salt, an ionic compound, is formed from the metal ion of the base and the non-metal ion from the acid. Recall that Arrhenius defined acids as substances that produce hydrogen ions in solutions, and bases as substances that produce hydroxide ions. You can see that neutralization reactions are good applications of the Arrhenius definitions of acids and bases. You may not be aware that when salt dissolves in water, a neutral solution is not always created. The pH of a salt solution depends on the strength of the acid and base involved in the reaction. This is the main focus of this lesson. Neutralization has a number of medical applications. Antacid tablets, which contain hydroxides or carbonates, are used to relieve stomach upsets by temporarily neutralizing a small amount of stomach acid. Planning Your Study You may find this time grid helpful in planning when and how you will work through this lesson. Suggested Timing for This Lesson (Hours) Neutralization ½ Salt Hydrolysis and the Equivalence Point ¾ Titrations and Selection of Indicators ¾ Calculating the pH at the Equivalence Point 1 Determining ASA Mass ¼ Key Questions What You Will Learn After completing this lesson, you will be able to predict whether salts will be neutral, acidic, or basic calculate the pH of the equivalence point of a neutralization reaction solve problems related to acid–base equilibrium, using data from titrations
Neutralization Neutralization reactions are a specific type of double displacement reaction. The hydrogen ion from the acid combines with the hydroxide ion of the base to form the water molecule. The metal ion from the base combines with the non-metal ion of the acid to create the salt. As indicated by the single-headed arrow, or “→”, neutralization reactions go to completion. The reaction reaches an equivalence point when the number of moles of H + is equal to the number of moles of OH . Note that the equivalence point is not when the number of moles of acid equals the number of moles of base. Stoichiometry can be used to determine unknown volumes or concentrations in neutralization reactions. The following three steps are involved: Step 1: Convert the known information to moles, usually by n = c × V . Step 2: Use the balanced equation to determine the mole ratio. S t ep 3 : A pp ly t h e m o l e r a t i o a n d u s n e t h e n u m b n e r o f m o l e s t o s o l v e f o r e i t h e r c o n ce nt r a t i o n or volume, by using the equation c V or V

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