13. The energy released in neutralization reaction which occurs between a strong acid and strong base is-
14. Antacids contain-
15. If pHpH of any solution is equal to zero then the solution will be
none of these
16. Which of the following is the weakest base?
17. Baking powder contains, baking soda and
potassium hydrogen tartaratecorrect
18. The difference in number of water molecules in gypsum and plaster of Paris is
19. If pHpH of any solution is equal to zero then the solution will be
none of these
20. A solution has pHpH 9. On dilution the pHpH value
none of these
Chemistry Notes Acid Bases and Salts for Class 9th Chapter 9 Sindh and Karachi board pdf download
What is Arrhenius’s theory of acids and bases? Why is the Arrhenius theory not satisfactory for acids and bases?
A Swedish chemist Svante Arrhenius, in 1984 placed his acid-base theory. According to this, acid is a species that contains hydrogen and can give hydrogen ions (H+) in an aqueous solution. For example, hydrochloric acid (HCl) gives H+ ion in its aqueous solution. The reaction is, HCl ⇔ H+ + Cl– As water accepts the H+ ion, it forms H3O+ as follows. HCl + H2O ⇔ H3O+ + Cl– According to Arrhenius, bases are the substances that produce OH– ions when it is dissolved in water. For example, NaOH is a base that gives OH– ions in water. NaOH ⇔ Na+ + OH– It also explains when acids and bases react together yield a neutral product salt and water. HCl + NaOH ⇔ NaCl + H2O This theory was very helpful to explain some acids and bases, but still, there were some limitations. Like, i) Arrhenius did not explain the behavior of acids and bases in non-aqueous solutions. ii) It only applies to substances that produce the only hydrogen (H+) ions or hydroxide (OH–) ions. iii) Arrhenius’s theory fails to explain acids such as AlCl3, and BF3, which have no ‘H’ atom.
What is Lewis’s theory of acids and bases?
In 1923, G.N, Lewis extended the definition of Bronsted-Lowry acids and bases. He noticed that Bronsted limited his theory on the transfer of protons (H+). Lewis proposed his theory to describe acids and bases. He explained what happens when an H+ ion combines with an OH– ion to form water.
He argued that proton accepts a pair of electrons from OH– to form a covalent bond. According to his theory, any substance that can act as an electron pair acceptor is called a Lewis acid. For example, H+ ion.
Any substance that can act as an electron-pair donor is called Lewis base. This theory expanded the family of acids. For example, any atom, ion, or molecule with vacant valence orbitals can act as Lewis acids.
For example, BF3 readily reacts with NH3.
List the main general properties of acids and bases.
a) Properties of acids: 1) Acids have a sour taste, vinegar gives the taste of acetic acid, and lemons and other citrus fruits contain citric acid. 2) They change the color of blue litmus to red. 3) Acids react with certain metals, such as (Zn, Mg, and Fe) to produce (H2) gas, for example, when diluted, (HCl) reacts with (Zn) metal, producing (H2) gas. Zn + 2HCl → ZnCl2 + H2 4) Acids react with carbonates and bicarbonates to produce carbon dioxide gas. CaCO3 + 2HCl → CaCl2 + H2O + CO2 5) Acids react with oxides and hydroxide of metals, forming salt and water. FeO + 2HCl → FeCl2 + H2O 6) Aqueous acid solutions conduct electricity. 7) They react with bases to form salts and water.
b) Properties of bases: 1) Bases have a bitter taste. 2) Bases have a slippery touch. 3) They change the color of red litmus to blue. 4) Aqueous solutions of bases conduct electricity. 5) They react with acids to form salts. When acids and bases are mixed in the right proportions, the acidic and basic properties disappear and new substances salt and water are formed and the reaction is a neutralization reaction.
Write the formulas of four strong acids and four weak acids.
Answer: Four strong acids:
Explain with illustrations what are strong acids and bases and weak acids and bases?
a) Strong acid: A strong acid is one, that completely dissociates in water and produces a large number of (H+) ions in an aqueous solution. For example, H2SO4 is a strong acid. H2SO4 + H2O → 2H+ + SO2-4
b) Weak acid: A weak acid is one, that partially dissociates in water and produces a small fraction of (H+) ions in water. For example, H2CO3 is a weak acid. H2CO3 + H2O ⇔ 2H+ + CO2-3
c) Strong base: A strong base is one, that completely dissociates in water and produces a large number of (OH–) ions in water. For example, NaOH is a strong base. NaOH + H2O → Na+ + OH–
d) Weak base: A weak base is one, that partially dissociates in water and produces a small fraction of (OH–) ions in water. For example, NH3 is a weak base. NH3 + H2O ⇔ NH4+ + OH–
Sulphuric acid (H2SO4) is a strong acid, (HSO4) is a weak acid? Account for the difference in strength?
H2SO4 is diprotic acid. It has two H+ ions for dissociation in water. So both H+ ionizes very easily in water so H2SO4 is a strong acid. While HSO4 is monoprotic and its H+ does not ionize in water. So it is a weak acid.
Define acidic, basic, and neutral solutions in terms of (H+) ion concentration. Indicate whether each of the following solutions will be acidic, basic, or neutral.
b) Strong acid and strong base. c) Strong acid and weak base. d) Weak acid and strong base. Answer: a. i) Acidic solution: If H+ ion concentration is greater than OH– then the solution is basic. ii) Basic solution: If H+ ion concentration is less than OH– then the solution is basic. iii) Neutral solution: If H+ and OH– ions concentrations are equal then the solution is neutral. b) Strong acid and strong base: When strong acid reacts with a strong base then a neutral solution is formed. For example, HCl + NaOH → H2O + NaCl c) Strong acid and weak base: When a strong acid reacts with a weak base then the solution is called acidic. For example, NH3 + HCl → NH4+ + Cl– d) Weak acid and strong Base: When a weak acid reacts with a strong base then the basic solution is formed. For example, CH3COOH + NaOH → H2O + CH3COO–Na+
What is salt? Give four examples of Salt?
It is an ionic compound formed by the neutralization of acids and bases. For example, HCl + NaOH → NaCl + H2O In this case, HCl is an acid, which reacts with base NaOH and gives a compound known as salt (NaCl) and water. NaCl is also called table salt which is used in our food. Salts are ionic compounds and have high melting and boiling points. For example, NaCl has a melting point of 801°C.
Four Examples of Salt: i) NaCl Table salt ii) NH4F Ammonium fluoride iii) MgCO3 Magnesium carbonate iv) Fe2(HPO4)3 Iron (III) Hydrogen Phosphate
Give an example of each of mono-protic acid, di-protic acid, and tri- protic acid?
i) Mono-protic acid: Acids, when dissolved in water, produce 1 mole of (H+) ion in solution, which is called mono-protic acids. For example, HCl, HNO3, and HCN are mono-protic acids.
ii) Di-protic acid: Acids, when dissolved in water, produce 2 moles of (H+) ions in solution, which are called di-protic acids. For example, H2SO4 is di-protic acid.
iii) Tri-protic acid: Acids, when dissolved in water, produce 3 moles of (H+) ions in solution, which are called tri-protic acids. For example, H3PO4 is a tri-protic acid.
Identify the following as weak or strong acids or bases?
a) NH3 b) H3PO4 c) LiOH d) HCOOH (formic acid) e) H2SO4 f) H2CO3 g) Ba (OH)2
Answer: a) Weak base b) Weak acid c) Weak base d) Weak acid e) Strong acid f) Weak acid g) Strong base
Define molarity? What is a molar solution?
Molarity: Molarity is the number of moles of a solute dissolve per dm3 of solution. It is denoted by M. M (Molarity) = number of moles of solute / dm3 or liter of solution.
Molar Solution: The molar solution is defined as one mole of solute dissolved in one liter of solution. For example, if 58.8g of NaCl is dissolved in enough water to make it 1 liter of the solution then the solution will be 1 molar.
What is the molarity of H2SO4 solution containing 9.8g of H2SO4 per 500 ml?
Answer: Data: Mass of H2SO4 = 9.8g Volume of solution = 500ml = 0.5 litre Molarity of H2SO4 = ? Solution: Molar mass of H2SO4 = 1 × 2 + 32 + 4 × 16 = 98g 98g of H2SO4 = 1 mol 1 g of H2SO4 = 1 / 98 9.8g of H2SO4 1/98 × 9.8 = 0.1 M Molarity of H2SO4 = No. of mol / Solution in litre = 0.1 / 0.5 = 0.2 M
Define pH? Explain why a neutral solution is said to have a pH of seven.
Answer: pH: the pH of the solution is defined as the negative logarithm of the hydrogen ion (H+) concentration or (H3O+) ion concentration in moles per liter. Mathematically it is written as, pH = -log [H+]
A neutral solution is said to have a pH of seven, it means the solution is neither acidic nor basic. pH is a measure of the number of Hydrogen ions (H+) in a solution. Ions are just atoms that have an electric charge on them, so (H+) is a hydrogen atom with a charge of 1. The amount of H+ in a neutral solution is about equal to a pH of 7 that is why the neutral solution is said to have 7 pH.
Give an equation to show the dissociation of water.
Dissociation of water: Water dissociates into an H+ ion or oxonium ion (H3O+). The equation for the dissociation of water is, H2O + H2O ⇔ H3O+ + OH- In the ionization of water, proton transfers from one water molecule to the other water molecule forming an H3O+ ion and OH– ion.
Define the term “Amphoteric”. Give an example?
Amphoteric: Any substance that behaves both as an acid and as a base is called amphoteric. For example, water reacts with NH3 (base), during this reaction water donate proton and act as an acid. H2O + HN3 → HN4+ + OH- However, when water reacts with HCl (acid), it behaves as a base by receiving a proton. H2O + HCl → H3O+ + Cl–