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 Their aqueous solutions 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

Strong Acids Strong acids are those which are completely dissociated (ionised) in dilute aqueous solution: HX (aq) H + (aq) + X – (aq) ≈ 0% ≈ 100% This means that such solutions are good conductors of electricity, owing to the presence of mobile ions. Hydrochloric acid is a typical example of a strong acid: HCl (aq) H + (aq) + Cl – (aq) Other common strong acids include sulfuric acid (H 2 SO 4 ) and nitric acid (HNO 3 ). H 2 SO 4 (aq) H + (aq) + HSO 4 – (aq) HNO 3 (aq) H + (aq) + NO 3 – (aq)

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

Acidic and Basic Strength the weaker the H-X bond, the more acidic the compound. Acidity increases from left to right across a row and from top to bottom down a group.

Weak Acids A weak acid is one which is only slightly dissociated into ions in dilute aqueous solution: HA (aq) H+ (aq) + A– (aq) ≈ 99% ≈ 1% A typical example of a weak acid is ethanoic acid, where the undissociated acid is in equilibrium with the ions: CH 3 COOH (aq)  H + (aq) + CH 3 COO – (aq) All organic acids are weak acids. Similarly aqueous carbon dioxide behaves as a weak acid: CO 2 (aq) + H 2 O (l)  H + (aq) + HCO 3 – (aq)

Strong Acid,HX

Weak Acid,HA

Other Common Inorganic Weak Acids Other common inorganic weak acids are: aqueous sulfur dioxide (SO 2 ) (analogous to aqueous CO 2 ) hydrofluoric acid (HF, as noted previously) hydrocyanic acid (HCN) AQUEOUS SOLUTIONS OF WEAK ACIDS AND BASES ARE WEAK ELECTROLYTES!!!

Differentiation of Strong and Weak Acids Strong and weak acids can be differentiated by comparing solutions of equal concentrations. The concentration of hydrogen ions in the solution of the weak acid will be considerably lower, giving rise to a number of differences that may be tested experimentally: A weak acid has a higher pH than a strong acid of equal concentration. Weak acids do not conduct electricity as well as strong acids of equal concentration, but they conduct electricity better than water. Weak acids react more slowly in typical acid reactions (such as those with a carbonate to give carbon dioxide or with an active metal to give hydrogen gas) than strong acids of equal concentration.

AQUEOUS ACIDS

Strong & Weak Acids

Strong Bases In the same way a strong base is one which is completely dissociated into ions in aqueous solution, like sodium hydroxide and barium hydroxide: NaOH (aq) Na + (aq) + OH – (aq) Ba(OH) 2 (aq) Ba 2+ (aq) + 2OH – (aq)

Weak Bases With weak bases an equilibrium exists between the base and the hydroxide ions so that, for example, ammonia is only partially converted to the hydroxide ion in aqueous solution: NH 3 (aq) + H 2 O (l)  NH 4 + (aq) + OH – (aq)

AQUEOUS BASE

Differentiation of Strong and Weak Bases Methods for differentiating strong and weak bases are similar to those for strong and weak acids; for solutions of equal concentration a strong base will have a higher pH and a greater electrical conductivity.

Chemical use of the term In chemistry care must be taken to use the terms strong and weak (meaning fully and partially dissociated) correctly and not as synonyms for concentrated and dilute (meaning containing a large or small number of moles in a given volume) as is done in everyday speech. The ‘chemical’ use of the term is also to be found, in ‘strong electrolyte’ and ‘weak electrolyte’. The term electrolyte means forming ions in aqueous solution allowing it to conduct electricity.

The term strong electrolyte refers to a substance that is completely converted to ions in aqueous solution (such as salts, strong acids and strong bases) whilst weak electrolyte refers to those only partially converted to ions (such as weak acids and bases). Note that only a very small fraction (< 1 in 108) of molecules in pure water is split up into ions, so it is a very weak electrolyte and hence a poor conductor of electricity.

Electrical Conductivity

Acidity in Soil We use neutralization to reduce the acidity in soil. Soil may be acidic because of the type of rock it came from or heavy use of fertilizers.

Acidity in Soil Most crops grow best when the pH of the soil is close to 7. If the soil is too acidic, crops grow badly or not at all. That could be disaster for farmers. To reduce the acidity of soil, the soil is treated with crushed limestone (CaCO 3 ) or lime (CaO) or slaked lime (Ca(OH) 2 ). A neutralization reaction takes place in the soil.