Neutralization

Main Idea: In a neutralization reaction, an acid reacts with a base

to produce a salt and water.

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Heartburn – Ew!

• If you were to experience heartburn or indigestion, you might take an antacid to relieve your discomfort.

• What kind of reaction occurs when magnesium hydroxide (Mg(OH)2), the active ingredient in milk of magnesia, contacts hydrochloric acid (H+ and Cl-)produced by the stomach?

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Neutralization

• When Mg(OH)2 and HCl react, a neutralization reaction occurs.

• A neutralization reaction is a reaction in which an acid and a base in an aqueous solution react to produce a salt and water.

• A salt is an ionic compound made from the cation from a base, and an anion from an acid.

• Neutralization is a double replacement reaction.

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Writing Neutralization Equations

• In the reaction between magnesium hydroxide and hydrochloric acid, magnesium replaces hydrogen in HCl and hydrogen replaces magnesium in Mg(OH)2.

Mg(OH)2 (aq)+ 2 HCl (aq) MgCl2 (aq) + H2O (l) Base + Acid Salt + water• Note that the cation from the base (Mg2+) is

combined with the anion from the acid (Cl-) in the salt MgCl2.

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Salt Hydrolysis

• Many salts react with water in a process known as salt hydrolysis.– The anions of the dissociated salt accept hydrogen

ions from water, or the cations of the dissociated salt donate hydrogen ions to water.

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Salts that Produce Basic Solutions

• Potassium fluoride is the salt of a strong base (KOH) and a weak acid (HF).

• KF (s) K+ (aq) + F- (aq)• The K+ ions do not react with water (no H+ to

give), but the F- ions act as a weak B-L base.• F- (aq) + H2O (l) HF (aq) + OH- (aq)

• The production of the OH- ions make the solution basic.

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Salts that Produce Acidic Solutions• Ammonium chloride is the salt of a weak base

(NH3) and a strong acid (HCl). • NH4Cl (s) NH4

+ (aq) + Cl- (aq)• The Cl- ions do not react with water because any

H+ it would want to gain would be immediately lost since HCl is a strong acid and undergoes 100% dissociation, but the NH4

+ ions act as a weak B-L acid.

• NH4+ (aq) + H2O (l) H3O+ (aq) + NH3 (aq)

• The production of the H3O+ ions make the solution acidic.

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Salts that Produce Neutral Solutions

• Sodium nitrate is the salt of a strong acid (nitric) and a strong base (sodium hydroxide).

• Little or no salt hydrolysis occurs because neither Na+ nor NO3

- react with water.

• Therefore, a solution of NaNO3 is neutral.

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Acidity of Salts Summary

• Salts can be acidic, basic, or neutral.• The easiest way to determine what kind of salt is

made is by looking at the acid and base that made it:– Strong acid + strong base = neutral salt (strength

evens out)– Strong acid + weak base = acidic salt (strength wins)– Weak acid + strong base = basic salt (strength wins)– Weak acid + weak base = undetermined (there is a

way to do it, but it’s too advanced for now)

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HOMEWORK

1) Give the name and formula of the acid and the base from which each salt was formed.

a) NaCl b) KHCO3 c) NH4NO2 d) CaS

2) What is a neutralization reaction? Sufferers of what medical condition benefit from neutralization reactions? Why?

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HOMEWORK

3) Write equations for the salt hydrolysis reactions occurring when the following salts dissolve in water. Classify each salt as acidic, basic, or neutral.

a) Ammonium nitrateb) Potassium sulfatec) Rubidium acetated) Calcium carbonate

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