Chapter 09: Acid Base Chemistry

(i) Ionization constant It is the extent of ionization of acids and bases which is much less than 100%. It is the quantitative measure of the strength of an acid or base. 'Ka' is ionization constant of acids and 'Ko' is ionization constant of a bases. HA + H2OF H2O* + A [HO*][A] f K. = [HA] (ii) Solubility product It is the product of concentration of ions raised to the exponent equal to the coefficient of the balanced equation. It is represented by • Ksp For example: (ill) Common ion effect The suppression of ionization of a weak electrolyte by adding a common ion to it is called common ion effect. For example: When HCl gas is passed through the saturated solütion of NaCl, due to formation of common Clions is increased and NaCl is crystallized out NaCC (8) Na (aq) + Cl (aq) H HC (g) (ag) + CC (a4) (iv) Acid-base Indicator An indicator is a substance that changes colour to mark a titration's and point. Acid base indicators exhibit one colour in acid and another in base. They are mostly weak organic acids or weak organic bases. For example: Phenolphthalein, methyl orange etc.

(i) Hydrolysis: The process in which substance dissolves in water, dissociate into ions and interact with water molecules is called hydrolysis. (i) It is a chemical process. (ii) Formation of new substances occurs. Example: Hydrolysis of ester Dissolution The process in which substance dissolves in solvent and form a homogeneous mixture. (i) It is a physical process. (ii) Formation of new substance does not occur Example: Dissolution of sugar in water. (ii) Difference of acidic and basic buffer solution. Acidic buffer: The buffer formed by mixing weak acid and salt of strong base is acidic buffer. Example: Mixture of CH:COOH and CH:COONa Basic Buffer: The buffer formed by mixing weak base and salt of strong acid is basic buffer Example: Mixture of NH4Cl and NH4OH

Conjugate acid: A specie formed when a base accepts a proton from the acid is called conjugate acid. Conjugate acid: A specie formed when an acid donates a proton to a base is called conjugate acid. In this reaction, Cl and HOt are conjugate acid- base pairs. HCC + H2O = HOt + Ce acid base Conjacid Conj.base

See Q.2 from theory.

There is an inverse relationship between the strength of an acid and strength of its conjugate base. The strong acid produces a weak conjugate base. Similarly, the strong base produces a weak conjugate acid. Example: HCl strong acid and its conjugate base 'Cl" is a weak base. 05. For the following three reactions, identify the reactants that are Arrhenius bases, Bronsted-Lowry bases, or Lewis bases. State which type of bases each reactant is. Explain your answers. (i) NaOHs) =Na (ag) + OH (ag) → F(ag) + H, O(a) Ans. (i) NaOHs) Na(aq) + OH (ag) In this reaction, NaOH dissociates in aqueous solution to produce OH ion. Hence, NaOH is an Arrhenius Base. (i) HF(a4) + H,0(0) Faq) + HO (ag) In this reaction, H2O behaves as Bronsted- Lowry base because it accepts a proton (H*) from HF. (i) H(ag) + NH 3(a4) =H4(aq) In this reaction, NH3 behaves as Lewis base because it donates the pair of electrons to Ht can

See Q.3 from theory.

(i) H2O+ HC=→H,0*+CE In this reaction, H20 behaves as a base because it accepts a proton (HT) from HCl. (ii) NH, + H,0 = ENH; + OH In this reaction, H2O behaves as an acid because it donates a proton (HT) to NH3. (ii) HNO, + H2O--H,0* + NO; In this reaction, H2O behave as a base because it accepts a proton (HT) from HNO3. (iv) CH,COOH + H,0==CH,COO- + H,0+ In this reaction, H2O behave as a base because it accepts a proton (Ht) from CH COOH

See Q.12 from theory.

Barium carbonate (BaCO3) dissolves more readily than CuS in acidic solution. When BaCO3 dissociates. BaCO, Ba* + CO3- Its conjugate base CO? reacts with Ht ions and form a weak acid BaCO3. CO3 + 2H* ÷H,CO, Hence, due to formation of H,CO3, solubility of BaCO3 increase. While in CuS. CuS -Cu2+ + S2- Its conjugate base does not react with Ht ions. Hence, its solubility is less than BaCO3. More over the Ksp of BaCO3 is more than the Kop of CuS. So, BaCO3 is more soluble than CuS.

See Q.15 from theory. A 5 = 4.8+ log [HA] = 5-4.8 log [HA] A = 0.2 log [HA] Taking antilog on both side [A] = antilog0.2 [HA] LA] =1.5848 [HA] Answer: The ratio of [A] to [HA] is 1.5848.

solution of a less soluble electrolyte suppresses (decreases) its ionization and the concentration of unionized species increase, which may come out as precipitate. That's why solubility of salt decrease due to common ion effect. State the basic principle of 09. Mention factors solubility product. affecting solubility product. Ans. The solubility product is the product of the concentrations of ions raised to an exponent equal to the co-efficient of the balanced equation. Ksp is the measure of dissociation of sparingly soluble salt. It is the product of molar solubilities of two ions at equilibrium stage. Factors affecting Ksp: Ksp is temperature (1) Temperature dependent value is usually very small at room temperature. (ii) Common ion effect: The solubility of slightly soluble salts decreases due to common ions. SLO BASED SHORT QUESTION ANSWERS Bronsted-Lowry concept are

To find: Ratio [A-] / [HA]

According to the Henderson-Hasselbalch equation:

So, the ratio of the concentration of conjugate base to weak acid is 1.58 : 1.

Equilibrium: S 2S

So, the solubility of PbI2 in water is 1.52 × 10-3 mol dm-3.

PbCr04 are mixed, the concentration of is increased according to Le- CrO 3(ag) Chatelier's principle. The solubility of PbCrO4 decreases as it precipitate out. This is due to common ion effect of CrO 4(ag) ion. Na, CrO 4(ag) 2Na* + CO*-

Equilibrium: 2S S

So, the Ksp of silver chromate is 1.1 × 10-12.

Yes, according to the Lewis acid-base concept, Boron trifluoride (BF3) can act as an acid. Because in BF3, central atom 'B' has incomplete octet or deficit of 2 electrons and it has ability to accept an electron pair

In Bronsted-Lowry theory, an acid is a proton (HT) donor, and a base is a proton acceptor This concept is broader than Arrhenius' Example: NH3 + H2O → NH4* + OH-

A conjugate acid-base pair ditters by one proton. When an acid donates a proton, it forms its conjugate base, and vice versa. Example: HCl / Cl and NH4* / NH3 are conjugate pairs. 01. What i meant by amphoteric substances? Ans. Amphoteric substances can act as both acids and bases depending on the environment. Example: Water (H2O) can accept or donate a proton.

When a base accepts a proton, it becomes a conjugate acid. When an acid donates a proton, it forms a conjugate base. Example: NH3 → NH4; HгCO3 → HСO3 Why are acids sour and bases

Due to their chemical nature: acids release Ht which activate sour taste receptors, while bases release OH which give a slippery, bitter feel

A Lewis acid is an electron pair acceptor, and a Lewis base is an electron pair donor Example: NH3 donates an electron pair to BF3, which accepts it. ionic product of water

at 25°C. It reflects self-ionization of water. pH and pOH is pH and how is it

pH is a measure of hydrogen ion concentration. It is calculated as:

Since HCl is a strong acid, it ionizes completely: [Ht] = 0.01 M pH = -log(0.01) =2 ionization Constant of Acids (ka)

By acid dissociation constant Ka. Stronger base has higher Ka and produces more Ht ions. The Ka is the ratio of concentrațion of acid ionized to the concentration of acid initially added.

Common Ion Effect Definition: The suppression of ionization of a weak electrolyte by adding a common ion to it is called common ion effect. Purification of sodium chloride: NaCl is purified by passing hydrogen chloride gas through brine (saturated solution of Nacl). Sodium chloride is fully ionized in the solution. Equilibrium constant expression for this process can be written as follows: NaC1(6) Na(ag) + Claq)

A buffer resists pH changes when small amounts of acid or base are added. It usually consists of a weak acid and its salt or weak base and its salt.

A mixture of CHCOOH and CH COONa is an acidic buffer that maintains pH around 4.75.

Buffers are used in blood, and fermentation, pharmaceuticals, laboratory titrations to maintain stable pH

Solubility Product Definition: The solubility product is the product of the concentrations of ions raised to an exponent equal to the co-efficient of the balanced equation. Example: The Ksp of PbSO4 is 1.6 × 10-16

bases like sodium chloride (NaCl). The conjugate base of a strong acid (Cl from HCl) is very weak and does not significantly react with water. The conjugate acid of a strong base (Nat from not NaOH) is also very weak and does significantly react with water. NaCl (s) = NO → Na"., + CC Nat is the conjugate acid of NaOH (a strong base) and does not affect the pH Cl is the conjugate base of Hcl (a strong acid and does not affect the pH.

Salt hydrolysis Definition: The breakdown of a salt (made up of weak acid or base) by reacting with water, resulting in the bond breaking in that salt which changes the pH of water is called hydrolysis. Acid-base indicators

Titration is a technique used to determine the concentration of an unknown acid or base using a solution of known concentration.

It is the point where moles of acid equal moles of base in titration. The pH at this point depends on the nature of acid/base.

Indicators change color near the equivalence point to help detect end of titration. Example: Phenolphthalein turns pink in base. DESCRIPTIVE QUESTIONS