ACIDS and BASES  Acid – Base theories  Naming acids and bases  Oxides  Reactions and properties of acids and bases  Strengths of acids and bases

Acid and Base Theories 1) Arrhenius Theory An acid is a substance that gives H + ion, when dissolved in water. For example, hydrochloric acid reacts with water to form hydrogen ions which are transferred to a water molecule to form a hydronium ion (H 3 O + ). But simply the reaction is: HCl H + + Cl -

Acids which have one ionizable hydrogen atom per molecule are called monoprotic acids. Example: HNO 3 H + + NO 3 - Acids which have two ionizable hydrogen atom per molecule are called diprotic acids. Example: H 2 SO 4 H + + HSO 4 − HSO 4 − ⇌ H + + SO 4 2− Acids which have three ionizable hydrogen atom per molecule are called triprotic acids. Example: H 3 PO 4 ⇌ H + + H 2 PO 4 – H 2 PO 4 – ⇌ H + + HPO 4 2– HPO 4 2– ⇌ H + + PO 4 3–

A base is a substance that gives OH - ion, when dissolved in water. NaOH → Na + + OH − Ca(OH) 2 → Ca OH - Reaction of NH 3 produce OH - : NH 3 + H 2 O → NH OH - so it is a base.

Limitations of the Arrhenius theory ONLY FOR AQUEOUS SOLUTIONS!!!!!

Acid and Base Theories 2) Bronsted-Lowry Theory An acid is a proton (hydrogen ion, H + ) donor. A base is a proton (hydrogen ion, H + ) acceptor. HCO 3 - and H 2 CO 3 HOH and OH - are conjugate acid- base pairs.

Conjugate acid-base pairs have only got 1 H + difference in their structures.

To determine whether a substance is an acid or a base, count the hydrogens on each substance before and after the reaction. If the number of hydrogens has decreased that substance is the acid (donates hydrogen ions). If the number of hydrogens has increased that substance is the base (accepts hydrogen ions)

A - becomes conjugate base of HA and in the reverse reaction it accepts a H from HZ to recreate HA. HZ + becomes a conjugate acid of Z and in the reverse reaction it donates a H to A - recreating Z Which pairs are conjugate acid-base pairs?

Example 1)What are the formulae for the conjugate acid of the following species? HS - CO 3 2- NH 3

Example 2) What are the formulae for the conjugate base of the following species? HS - CO 3 2- NH 3 H 2 SO 4

Acid and Base Theories 2) Bronsted-Lowry Theory The Bronsted-Lowry theory doesn't go against the Arrhenius theory in any way - it just adds to it.

Naming Acids and Bases A. Naming Acids: The name of the acid is determined based on the name of the anion, specifically, based on the ending of the anion name. The three possibilities are listed here: Anion Name Acid Name -ideHydro-ic acid -ite-ous acid -ate-ic acid

FluorideF-F- ChlorideCl - BromideBr - IodideI-I- SulfideS 2- CyanideCN-CN- SulfiteSO 3 2- NitriteNO 2 - PhosphatePO 4 3- NitrateNO 3 - SulfateSO 4 2- PerchlorateClO 4 - ChlorateClO 3 - CarbonateCO 3 2- Common Anions

B. Naming Bases Simply use the normal rules for naming compounds; ionic or covalent depending on the elements in the compound. Example: NaOH: Sodium hydroxide Ca(OH) 2 : Calcium hydroxide NH 3 : Ammonia

Example: a) Name the following acids and bases: NaOH: H 2 SO 3 : H 2 S : H 3 PO 4 : NH 3 : HCN: Ca(OH) 2 : H 3 P: Sodium hydroxide Sulfurous acid Hydrosulfuric acid Phosphoric acid Ammonia Hydrocyanic acid Calcium hydroxide Hydrophosphoric acid

b) Write the formulas of the following acids and bases: Hydrofluoric acid: Carbonic acid: Lithium hydroxide: Nitrous acid: Sulfuric acid: Beryllium hydroxide: Hydrobromic acid: HF H 2 CO 3 LiOH HNO 2 H 2 SO 4 Be(OH) 2 HBr

Some common acids Sulfuric acid: Nitric acid (kezzap): Hydrochloric acid(tuz ruhu) Acetic acid/ethanoic acid/ vinegaric acid Formic acid/methanoic acid »(in ants’ saliva) H 2 SO 4 HNO 3 HCl CH 3 COOH HCOOH

Some common bases/alkalis Sodium hydroxide(caustic soda): Potassium hydroxide: Magnesium hydroxide (milk of magnesia) Calcium hydroxide Ammonia NaOH KOH Mg(OH) 2 NH 3 Ca(OH) 2

Oxides Nonmetal Oxides Metal Oxides CO 2, SO 2, SO 3 etc. show acidic properties (acid anhydride) CO, NO, N 2 O are neutral (have 1 oxygen atom in the formula) Na 2 O, BaO etc. show basic properties (basic anhydrides) Amphoteric metals show both basic and acidic properties such as Al and Zn

Acidic Property of Nonmetal Oxides The oxides of nonmetals are usually acidic except NO, N 2 O and CO (They are neutral) When acidic oxides of nonmetals dissolve in water, they form acidic solutions. CO 2 + H 2 O H 2 CO 3 SO 3 + H 2 O H 2 SO 4 N 2 O 5 + H 2 O 2HNO 3 P 4 O 10 + H 2 O 4H 3 PO 4 Acidic nonmetal oxides react with bases to form salts. SO 3 + 2KOH K 2 SO 4 + H 2 O

ACIDIC OXIDES Carbon dioxide dissolved in water is in equilibrium with carbonic acid: equilibrium CO 2 + H 2 O ⇌ H 2 CO 3 (the equilibrium rxn happens in our blood)

NEUTRAL OXIDES They don’t react with water, acids, and bases.

Basic Properties of Metal Oxides Oxides of metals are usually basic. Na 2 O + H 2 O 2NaOH BaO + H 2 O Ba(OH) 2 Basic oxides react with acids to form salts. CaO + H 2 SO 4 CaSO 4 + H 2 O

Amphoteric Oxides Oxides amphoteric metals are also amphoteric. Al 2 O 3 + HCl AlCl 3 + H 2 O Al 2 O 3 + 2NaOH + 3H 2 O 2NaAl(OH) 4 (sodium tetrahydroxoaluminate)

Properties and Reactions of Acids and Bases A.Properties of Acids: Are corrosive They taste sour They form solutions w/ pH less than 7 at 25°C. They turn litmus dye from blue to red They conduct electricity (electrolyte) They react with active metals to form salt and H 2 gas. Mg + 2HCl MgCl 2 + H 2

The acids which do not contain oxygen in their structures can not react with semi noble metals Cu, Hg, Ag.The oxy acids (ACIDS HAVING OXYGEN IN THEIR STRUCTURES)react with these metals producing gases other than H 2. Cu + 2H 2 SO 4  CuSO 4 + SO 2 + 2H 2 O 3Ag + 4HNO 3  3AgNO 3 + NO + 2H 2 O They react with metal carbonates and hydrogen carbonates(bicarbonate ion) to give a salt, water and carbon dioxide, which appears as effervescence (bubbles). Na 2 CO 3 + 2HCl NaCl + H 2 O + CO 2 CH 3 COOH (aq)+NaHCO 3 (aq)  NaCH 3 COO(aq) +H 2 O (l) + CO 2 ethanoic acid metal hydrogen salt water carbon carbonate dioxide

They react with bases to form salts and water. HCl + NaOH  NaCl + H 2 O (neutralization) H + (aq) + OH - (aq)  H 2 O(l) (net ionic equation)

B. Properties of Bases They have bitter taste Aqueous solutions of bases, known as alkali, have a slippery feel. They turn the litmus dye from red to blue They react with fats in the skin to form soaps They conduct electricity (electrolyte) The most common bases are the oxides, hydroxides and carbonates of metals, but a number of other compounds, such as ammonia also acts as a base.

They only react with amphoteric metals: Zn, Al Zn + 2NaOH  Na 2 ZnO 2 + H 2 2Al + 6 NaOH  2Na 3 AlO 3 + 3H 2 If they are soluble in water they give a solution with pH>7 (at 25 o C). They react with acids to form a salt. CaO (s) + 2 HCl (aq)  CaCl 2 (aq) + H 2 O (l) base acid salt water

Amphoteric metals can react with both acids and bases, such as Al, Zn, Sn, Pb, Cr Al + 6HCl AlCl 3 + 3H 2 2Al + 6NaOH 2Na 3 AlO 3 + 3H 2 Oxides and hydroxides of amphoteric metals are also amphoteric. Al 2 O 3 + HCl AlCl 3 + H 2 O Al 2 O 3 + 2NaOH + 3H 2 O 2NaAl(OH) 4 ZnO + 2 HCl ZnCl 2 + H 2 O ZnO + 2NaOH + H 2 O Na 2 Zn(OH) 4

Neutralization

Examples of Acids & Bases Acids HCl H 2 SO 4 HNO 3 Juices, Soda NaOH Ca(OH) 2 KOH Soap, Ammonia, Baking Soda Bases

Relative Strengths of acids and Bases The strength of an acid depends on how easily the proton, H + is lost or removed from an acid Two factors determine the acidic strength: 1.The polarity of the bond with H atom: The more polarized the bond is, the more easily the proton is removed and greater the acidic strength. 2.The size of the atom X (in HX): The greater the atom X, the weaker is the bond and greater the acidic strength.

Periodic Trends for Binary Acids: Down a group: Sizes of the atoms increase. HF HCl Acidic strength increases HBr HI Across a period: Polarity of the bond increases. CH 4 NH 3 H 2 O HF Acidic strength inreases.

Oxyacids: HOF HOCl Acidic strength decreases. H-O HOBr bond ionizes HOI more easily when the oxygen atom is bonded to a more electronegative atom.

For a series of oxyacids: HClOHClO 2 HClO 3 HClO 4 Acidity increases As the number of oxygen atoms increases, The oxidation number of central atom (Cl) increases. This increases the ionization of O-H bond. Therefore, acidic strength increases.

Polyprotic Acids and Their Anions: H 3 PO 4 H 2 PO 4 - HPO 4 2- H 2 CO 3 HCO 3 - Acidity decreases H 2 SO 4 HSO 4 -

Organic Acids Organic acids have carboxyl group (COOH). They are weak acids. Example: HCOOH: Formic acid CH 3 COOH: Acetic acid

Basic strength As the volume of the metal increases, it becomes easier to ionize the OH - ion and the basic strength increases. LiOH NaOH KOH Basic strength increases