Lesson #7: Introduction to Acids and Bases

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1 Lesson #7: Introduction to Acids and Bases

2 Acid (As Defined by Arrhenius) Properties of Acids In 1887 Swedish Chemist Svante Arrhenius defined an Acid as: A Compound (Ionic or Molecular) that dissociates (separates) when dissolved in water to yield Hydrogen Ions (H + ) The H + ions then react with water to form Hydronium Ions H 3 O + Aqueous (aq) Sour Taste (be careful tasting acids) Conduct electricity React with ALL Metals to produce Hydrogen Gas (H 2 ) Will produce Carbon Dioxide when reacting with a Carbonate Strong Acids are corrosive Acid strength is determined by its concentration in water and its percent ionization The more the acid dissociates, the stronger it becomes

3 Naming Acids There are 2 basic rules to naming an Acid (Yay more naming rules) Note: You will only use these rules for reactions that take place in solution (aqueous state) 1. Hydrogen + Another Element Add the prefix Hydro and the suffix ic acid to the second element (ex) HF (aq) is called Hydrofluoric Acid 2. Hydrogen + A Polyatomic Ion Use the suffix ic acid on the polyatomic ion (ex) H 2 SO 4(aq) is called Sulfuric Acid

4 A Base (As Defined by Arrhenius) In 1887 Arrenhius defined a Base as: An Ionic Compound that dissociates when dissolved in water to yield Hydroxide Ions (OH-) Properties of Bases Aqueous (aq) All contain OH- ions All taste bitter All conduct electricity Feel slippery because they dissolve oils and fatty acids in skin Destroy protein Do not react with Zinc Are often referred to as Alkaline Remember Bases are Ionic Compounds!

5 The case of Ammonia (an exception to Arrhenius Theory) Ammonia (NH 3(aq) or H 3 N (aq) ) is a common BASE that behaves slightly differently than typical bases Ammonia DOES NOT dissociate when dissolved in water Instead, Ammonia triggers the dissociation of water that then yields hydroxide (OH - ) ions

6 The ph Scale A scale used to measure the strength of an acid or a base

7 the smaller the ph value, the stronger the acid is (substance is more acidic ) (ex) ph = 3 is a stronger acid than ph = 5 the larger the ph the stronger the base is (substance is more basic or alkaline ) (ex) ph = 13 is a stronger base than ph = 11 a substance with a ph of 7 is considered neutral and is neither an acid nor a base (ex) distilled water (H 2 O) should have a ph of 7 and be neutral Each ph value represents a 10X increase or decrease in Acid / Base strength

8 Indicators Chemicals that are used to identify the presence of an Acid or a Base There are two classes of Indicators: General Indicators are used to identify whether a substance is Acidic or Basic BUT are UNABLE to identify the relative strength of the acid or base Specific Indicators are able to identify whether a substance is Acidic or Basic AND determine the relative strength of the acid or base

9 The Neutralization Reaction A reaction in which an Acid and a Base combine to form a salt and water HCl (aq) + LiOH (aq) LiCl + H 2 O (Acid) (Base) (Salt) The Hydrogen (H + ) Ion from the Acid combines with the Hydroxide (OH - ) Ion from the Base to form water A Salt is an ionic compound formed from the anion of the acid and the cation of the base Neutralization Reactions are Double Displacement Reactions