Acid base and Salt Dalal Simplified ICSE Chemistry Class-10

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Acid base and Salt Dalal Simplified ICSE Chemistry Class-10

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Question 1.

Define the following as per ionic theory with examples and ionic equations wherever relevant
(1) acid
(2) base
(3) alkali
(4) neutralization
Answer:
(1) Acid — An acid is a compound which when dissolved in water yields – hydronium ions (H₃O⁺ ) as the only positively charged ion.

(2) Base — A base is a compound which reacts with hydronium ions of an acid – to give salt and water

CuO + 2HCl → CuCl₂ + H₂O

(3) Alkali — An alkali is a compound which when dissolved in water yields Hydroxyl ions (OH^–) as they are negatively charged ions.

Alkali is a base soluble in water.

(4) Neutralization — | H⁺| ions of an acid completely or combine with |OH⁺| ions of a base to give salt and water only.

Acid + Base → Salt + Water

HCl + NaOH → NaCl + H₂O

Question 2.

Differentiate between:

Organic and inorganic acids
Hydracids and oxyacids with examples.

Answer:
(1)
Organic acids – Those acids which are derived from plants, e.g., citric acid, acetic acid, tartaric acid Inorganic acids – Acids derived from minerals e.g. HCl₂,h₂SO₄(2)
Hydracids – Acids containing hydrogen and a non-metallic element other than oxygen, e.g. HCl, HBr, HI.
Oxyacids – Acids containing hydrogen, another element and oxygen, e.g. HNO₃, H,SO₄.

Question 3.

State on what basis does the strength of an acid and an alkali depend on.
Answer:
Strength of acids depends upon concentration of hydronium ion |H₃O⁺| present in an aqueous solution
of an acid. Strength of alkali depends on the concentration of the hydroxyl ions |OH^–| present in an aqueous solution of an alkali.

Question 4.

Differentiate between (1) strong and weak acid (2) strong and weak alkali with suitable examples and ionic equations.
Answer:
(1) Strong Acid – Is an acid which dissociates – almost completely in aqueous solution there by producing a – high concentration of hydrogen [H⁺] ions [or H₃O⁺ions]
Examples: Hydrochloric, Sulphuric and Nitric acid.

Weak Acid – Is an acid which dissociates – only partially in a aqueous solution thereby producing a – low concentration of hydrogen [H⁺] ions [or H₃O⁺ ions].

(2) Strong Alkali – Is an alkali which dissociates – almost completely in aqueous solution thereby producing a – high concentration of hydroxyl [OH^–] ions.

Examples: Lithium, Sodium and Potassium hydroxide
Weak alkali – Is an alkali which dissociates – only partially in aqueous solution thereby producing a – low concentration of hydroxyl [OH^– ] ions.

Examples: Ammonium hydroxide and Calcium hydroxide.

Question 5.

Name the ions formed when – HCl ; HNO₃ ; H₂SO₄ ; CH₃COOH ; NaOH and NH₄OH ionise in aq. soln.
Answer:

Question 6.

State giving reasons which is a stronger acid – dil. HCl or cone. H₂CO₃.
Answer:
Dil. HCl is a stronger acid than cone. H₂CO₃Reason: HCl ionises almost completely in aqueous solution thereby producing a high concentration of Hp ions in aqueous solution. On the other hand, H₂CO₃ ionises to a very small extent producing a low
concentration of HO⁺ ions. More the concentration of H₃O⁺ ions in solution, stronger is the acid. Hence dil. HCl is a stronger acid than cone. H₂CO₃.

Question 7.

State why the basicity of acetic acid is one and acidity of calcium hydroxide is two.
Answer:
Basicity of an acid is the number of hydrogen ions which can be produced from one molecule of the acids on complete dissociation. Acetic acid, CH.COOH gives one H⁺ per molecule the acid, hence acetic acid is monobasic i.e., its basicity is one.

Acidity of a base is the number of hydroxyl ions which can be produced from one molecule of the base on complete dissocation. Ca(OH)₂ (calcium hydroxide) gives two hydroxyl ions per molecule of the base, hence calcium hydroxide is diacidic i.e., its acidity is two.

Question 8.

Give three reasons with equations wherever required, why sulphuric acid is a dibasic acid.
Answer:
Sulphuric acid (H₂SO₄) is a dibasic acid as explained below:

(1)
It ionises in aqueous solution to produce two hydrogen ions per molecule of the acid.

It contains two replace all hydrogen ions per molecule of the acid.

Question 9.

State how acids are defined as per Arrhenius’s and Lowry – Bronsted’s theory.
Answer:
Arrhenius Theory –
Acids are substances which – dissociate in aqueous solution to give H⁺ ions.
Strong acids dissociate – almost completely, while weak acids dissociate partially.

Question 10.

Oxygen atom in water has two Hone pair of electrons’. Explain the meaning of the term in italics. With the help of an electron dot diagram show the formation of hydronium ion and ammonium ion from a water molecule and an ammonia molecule respectively.
Answer:
A pair of electrons not shared with any other atom for bond formation is called a lone pair of electrons. In water, the central atom – oxygen has two lone pair of electrons as shown ahead:

Structure of water molecule

Formation of hydronium ion- (H₃O⁺): When an acid is dissolved in water the proton (H⁺) released by the acid add onto the lone pair electrons of the oxygen atom of a water molecule. The proton (H⁺) accepts the lone pair of electrons forming a coordinate bond (shown by an arrow).
HCl → H⁺ + Cl^–Water Proton Hydronium ion

Formation of ammonium ion (NH₄⁺): When ammonia gas is dissolved in water, the proton released by water adds onto the lone pair of electrons of the nitrogen atom of the ammonia molecule. The proton (H⁺) accepts the lone pair of electrons forming a coordinate bond (shown by an arrow).

Question 11.

State how you would obtain:

Sulphuric acid from an acidic oxide
KOH from a basic oxide.

Answer:
(1)

Question 12.

State two chemical properties each with equations of a solution containing
(1) H⁺ ions
(2) OH
Answer:
(1) Properties of a solution containing H⁺ ions: Acids when dissolved in water produce H₂O⁺ or H ions. Typical chemical properties of aqueous solution of acids are:

(a) Neutralisation: H⁺ ions react with OH ions from alkalies to give water

(b) Reaction with active metals: Active metals like Al, Zn, Fe, etc., react with dil. acids (HCl, H₂SO₄) to give hydrogen gas. In this reaction H⁺ is reduced to H, by the active metal. For example,

(2) Properties of solution containing OH^– ions: Alkalies when dissolved in water produce OH” ions. Typical reaction of aqueous solution of alkalies are;

(a) Neutralisation: OH⁺ ions react with H⁺ ions from acids to give water.

(b) Reaction with solutions of metallic salts: Hydroxides of metals other than Group 1 and 2 are generally insoluble in water. Such hydroxides are precipitated from their respective salt solutions by OH” ions. For example,

Question 13.

Give equations for the decomposition of a metallic
(1) chloride
(2) nitrate with cone. H₂SO₄.
Answer:
(1) Reaction of cone. H₂SO₄ with metallic chloride:

(2) Reaction of cone. H₂SO₄ with metallic nitrate

Question 14.

State in the above reactions a reason for the formation of the respective acids from cone. H₂SO₄.
Answer:
The reason for the formation of the respective acids from cone. H₂SO₄ is the volatility of the acid formed. At room temperature or above HCl is a gas while HNO₃, which is a liquid at room temperature, volatileses at the reaction temperature (w 200°C).

Question 15.

Convert
(1) NaHCO₃
(2) Na₂CO₃ to unstable carbonic acid by action with dil. H₂SO₄.
State the reason why ammonia is evolved when an ammonium salt and alkali are heated.
Answer:

2NaHCO₃ + H₂SO₄ (dil.) → Na₂SO₄ + 2H₂CO₃
Na₂CO₃ + H₂SO₄ (dil.) → Na₂SO₄ + H₂CO₃

Ammonia is evolved when an ammonium salt and alkali are heated.

This is because a non-volatile base, Ca(OH)₂ displace a volatile base, NH₄OH which decomposes to given NH₃ and H₂O.

Question 16.

Define pH value. What would you say about the pH of a solution in which (i) H⁺ ions = OH^– ions

evolves CO₂when heated with Na₂CO₃
OH” ions > H⁺ ions.

Answer:
pH value: The pH value of a solution is defined as the negative logarithm (to the bsise 10) of the hydrogen ion concentration expressed in mol L^-1. Thus,
_PH = -log₁₀ [H⁺]
Where [H⁺] stands for hydrogen ion concentration in mol L^-1.

A solution in which [H⁺] = [OH^–], is neutral with pH = 7.
A solution which evolves CO₂ with NaCO₃ is acidic in nature with pH < 7.
A solution in which [OH^–] > [H⁺] is basic in nature with pH >7.

Question 17.

State whether litmus is a common acid-base indictor or a universal indicator.
Answer:
Litmus is a common acid-base indicator. It is not a universal indicator.

Question 18.

State the colour change in a neutral litmus in presence of
(1) acidic
(2) alkaline medium.
Answer:
Neutral litmus is purple in colour

In acidic medium colour of neutral litmus changes from purple to red.
In alkaline medium colour of neutral litmus changes from purple to blue.

Question 19.

State the colour change in a universal indicator e.g. pH paper on

slightly acidic soil
slightly alkaline soil
dairy milk
human blood tested for medical diagnosis.

Answer:

In slightly acidic soil colour of universal indicator changes to yellow.
In slightly alkaline soil colour of universal indicator changes to blue.
In dairy milk colour of universal indicator change to green.
In human blood colour of universal indicator changes to green (pH = 7.3).

Question 20.

Define
(1) salt
(2) normal salt
(3) acid salt – with relevant examples and equations.
Answer:
(1) Salts: A salt is a compound formed by partial or complete replacement of the replaceable hydrogen ions of an acid by a metallic ion or ammonium ion.

(2) Normal salt: The salt formed by complete replacement of the replaceable hydrogen ions present in a molecule of the acid by metallic or ammonium ion. For example,

2NaOH(aq) + H₂CO₃(aq)→ Na₂CO₃(aq) + 2H₂O (l)

NH₄OH(aq) + HCl(aq)→ NH₄Cl(aq) + H.O (l)

(3) Acid salt: The salt formed by partial replacement of the replaceable hydrogen ions present in a molecule of the acid by metallic or ammonium ion. For example,

NaOH(aq) + H₃PO₄(aq) → NaH₂PO₄(aq) + H₂O(l)
2NaOH(aq) + H₃PO₄(aq)→Na₂HPO₄(aq) + 2H₂O (l)
KOH(aq) + H₂SO₄(aq)→ KHS0₄(aq) + H₂O(l)
NH₄OH(aq) + H₂CO₃(aq)→NH₄HCO₃(aq) + H.O (l)

Question 21.

State:

the formation
the components of – a basic salt.

State which of following salts is an – acid, normal or basic salt.

bleaching powder
potassium mercuric iodide
sodium sulphite
sodium hydrogen sulphite
sodium silver cyanide
basic lead nitrate
potassium zincate
alum
calcium bicarbonate
basic copper chloride
trisodium phosphate.

Answer:

(1) Formation of a basic salt: A basic salt is formed by partial replacement of hydroxyl group of a diacidic or triacidic base with an acid radical (or an anion other than OH).

(2) Components of a basic salt: A basic salt contains a cation (other than H⁺ ion), a hydroxyl ion (OH^– from base) and an anion (other than OH^– ion). For example,

Bleaching powder, CaOCl, (Normal salt/Mixed salt)
Potassium mercuric iodide, K₂(HgI₄) .
(Normal salt/Complex salt)
Sodium sulphate, Na₂SO₄ (Normal salt)
Sodium hydrogen sulphite, NaHSO₃ (Acid salt)
Sodium silver cyanide, Na[Ag(CN)₂]
(Normal salt/Complex salt)
Basic lead nitrate, Pb(OH)NO₃ (Basic salt)
Potassium zincate, K₂ZnO₂ (Normal salt)
Alum or potash alum, K₂SO₄.Al₂(SO₄)₃.24H₂O
(Normal salt/Double salt)
Calcium bicarbonate, Ca(HCO₃)₂ (Acid salt)
Basic copper chloride, Cu(OH)Cl (Basic salt)
Trisodium phosphate, Na₃PO₄ (Normal salt)

Question 22.

Name three (1) sulphates (2) chlorides insoluble in water and – two (1) oxides (2) carbonates soluble in water.
Answer:
(1) Three sulphates insoluble in water
Lead sulphate (PbSO₄), Calcium sulphate (CaSO₄), and Barium sulphate (BaSO₄).

(2) Three chloride insoluble in water
Silver chloride (AgCl), Lead chloride (PbCl₂), and Mercury chloride (Hg₂Cl₂ or HgCl).

(1) Two oxides soluble in water
Sodium oxide (Na₂O), and Potassium oxide (K₂O)

(2) Two carbonates soluble in water
Sodium carbonate (Na₂CO₃), and Ammonium carbonate [(Na₄)₂CO₃]

Question 23.

State the method only, generally used for the preparation of the following salts
(1) Zn(NO₃)₂
(2) NH₄Cl
(3) ZnSO₄
(4) ZnS
(5) CaCO₃
(6) FeCl₃
(7) PbCl₂(8) Pb(NO₃)_2^–Answer:

Salt	Method of preparation
1. Zn(NO₃)₂	Neutralisation of insoluble base by acid/Decomposition of insoluble carbonate by acid
2. NH₄Cl	Neutralisation (titration) of soluble base by acid/Decomposition of soluble carbonate by acid
3. ZnSO₄	Neutralisation of insoluble base by acid/Decomposition of insoluble carbonate by acid
4. ZnS	Direct combination (Synthesis)/Double decomposition (Precipitation)
5. CaCO₃	Double decomposition (Precipitation)
6. Fecl₃	Direct combination (Synthesis)/
7. pbCl₂	Double decomposition (Precipitation)
8. Pb(NO₃)₂	Neutralisation of insoluble base by acid/Decompostion of insoluble carbonate by acids

Question 24.

Give balanced equations for the preparation of the following salts –

(a)
(1) CuSO₄(2) NaHSO₄
(3) Na₂SO₄
(4) FeSO₄(5) BaSO₄
(6) PbSO₄ – using dil. H₂SO₄(b)
(1) NaHSO₄
(2) CuSO₄ – using cone. H₂SO₄.
Answer:
(a) Using dil. H₂SO₄

CuO (s) + H₂SO₄ (aq) → CuSO₄ (aq) + 2H₂O (l)
NaOH (aq) + H₂SO₄ (aq) → NaHSO₄ (aq) + H₂O(l)
2NaOH (aq) + H₂SO₄ (aq)→Na₂SO₄ (aq) + 2H₂O(l)
Fe (s) + H₂SO₄ (aq)→ FeSO₄ (aq) + H₂ (g)
BaCl₂ (aq) + H₂SO₄ (aq)→ BaSO₄ (s) + 2HCl (aq)
Pb(NO₃)₂ + H₂SO₄ (aq)→ PbSO₄ (s) + 2HNO₃ (aq)

(b) Using cone. H₂SO₄

Question 25.

Starting from insoluble ZnO how would you obtain insoluble ZnCO₃ by precipitation.
Answer:
ZnO (s) + 2HCl (aq)→ ZnCl₂ (aq) + H₂O(l)
ZnCl₂ (aq) + Na₂CO₃ (aq)→ ZnCO₃ (s) + 2NaCl (aq)

Dissolve zinc oxide in minimum quantity of dil. HCl. Add to it a saturated solution ofNa₂CO₃ in water till
no more precipitation takes place. Filter and dry the ZnCO₃ so obtained.

Question 26.

Give balanced equations for the action of a dilute acid on
(1) zinc carbonate,
(2) potassium bicarbonate for the preparation of the respective salt.
Answer:

Zinc carbonate
ZnCO₃ + 2HNO₃ → Zn(NO₃)₂ + H₂O + CO
Potassium bicarbonate
2KHCO₃ + H₂SO₄ → K₂S0₄ + 2H₂O + 2CO₂

Question 27.

Give balanced equations for the decomposition of
(1) calcium bicarbonate by dil. HCl,
(2) calcium carbonate by dil. HNO₃,
(3) sodium sulphite by dil. H₂SO₄,
(4) zinc sulphide by dil. H₂SO₄.

Answer:

Ca(HCO₃)₂ + 2HCl→ CaCl₂ + 2H₂O+ 2CO₂
CaCO₃ + 2HNO₃ → Ca(NO.)₂ + H₂O+ CO₂
Na₂SO₃ + H₂SO₄ (dil.) → Na₂SO₄ + H₂O+ SO₂
ZnS + H₂SO₄ →ZnSO₄ + H₂S

Question 28.

State what will be the effect of each of the following solution on blue litmus –
(1) K₂CO₃ soln
(2) KCl soln.
(3) NH₄NO₃Answer:

K₂CO₃is a salt of a strong base (KOH) and weak acid (H₂CO₃). Hence its aqueous solution will be basic in nature. It will have no effect on blue litmus solution.
KCl is a salt of a strong acid (HCl) and a strong base (KOH). Hence its aqueous solution will be neutral in nature. It will have no effect on blue litmus solution.
NH₄NO₃ is a salt of a strong acid (HNO₃) and weak base (NH₄OH). Hence its aqueous solution will be acidic in nature. It will turn blue litmus solution red.

Question 29.

Select the correct acid, base or salt from the list in bracket for each of the statements given below:

An example of an acid derived from a mineral is……….. (citric acid / nitric acid / acetic acid)
Ans. Nitric acid

An example of a base which is not a alkali is….. (caustic soda / zinc hydroxide / liquor ammonia / caustic potash)
Ans. Zinc hydroxide

An example of a strong acid is dilute……… (acetic acid / sulphuric acid / tartaric acid / carbonic acid)
Ans. Sulphuric acid

An example of a weak alkali is…. (potassium hydroxide / calcium hydroxide / sodium hydroxide) solution.
Ans. Calcium Hydroxide

An acid having basicity 1 is……… (carbonic acid / acetic acid / sulphurous acid)
Ans. Acetic acid

An acid obtained by dissolving sulphur trioxide in water is…. (sulphurous acid / sulphuric acid oleum)
Ans. Sulphuric acid

A volatile acid obtained when nitre reacts with nonvolatile concentrated sulphuric acid on heating is (hydrochloric acid / sulphuric acid/ nitric acid)
Ans. Nitric acid

A base obtained when lead nitrate undergoes thermal decomposition is……. (trilead tetroxide / lead (IV) oxide/ lead (II) oxide. .
Ans. Lead (II) oxide

An acid obtained when concentrated nitric acid is heated with sulphur is…….. (sulphurous acid / sulphuric acid / nitrous acid)
Ans. Sulphuric acid

The more volatile acid obtained when the less volatile acid reacts with sodium bicarbonate is……… (sulphuric acid / carbonic acid / nitric acid)
Ans. Carbonic acid

The insoluble base obtained when sodium hydroxide reacts with iron (III) chloride is…. (iron (II) hydroxide / iron (III) hydroxide / iron (II) oxide)
Ans. Iron (III) hydroxide.

A solution whose pH is above 7 is….. (vinegar / milk / liquor ammonia.
Ans. Liquor Ammonia

The salt formed when sulphuric acid reacts with excess caustic soda solution is…… (sodium bisulphite / sodium sulphate / sodium sulphite / sodium bisulphate).
Ans. Sodium sulphate

An example of an acid salt is……. [CH₃COONa/NaNO₃/ Na₂HPO₄/NaKCO₃]
Ans. Na₂HPO₄

An example of a soluble salt is ……… (AgCl / PbSO₄ /CaSO₄ / CaCl₂)
Ans. CaCl₂

An example of an insoluble salt is….. (Na₂CO₃ \ K₂CCl,/ MgCO₃ / (NH₄)₂ CO₃)
Ans. MgCO₃

A salt prepared by neutralization in which titration is involved is…….. (MgCl₂ / CaCl₂ / NH,Cl / CuCl₂)
Ans. NH₄Cl
An insoluble salt prepared by direct combination or synthesis is……. [FeCl₃ / FeSO₄ / FeS/Fe(NO₃)₂] Ans. FeS

A salt prepared by precipitation i.e. by double decomposition of two salt solutions is………… (Na₂SO₄ /PbSO₄ / ZnSO₄ / CuSO₄)
Ans. PbSO.
A salt prepared by simple displacement i.e. action of dilute acid on a metal is____ (PbCl₂/ CuCL, / AlCl₃ / HgCl)
Ans. AlCl₃
Decomposition of calcium hydrogen carbonate with…. [dil. HNO₃ /dil. HCl/dil. H₂SO₄] results in formation of calcium chloride.
Ans. dil.HCl

Action of dilute acid on a metallic sulphide results in evolution of____ [SO₂/H₂S/CO₂] gas.
Ans. H₂S

A salt which on hydrolysis produces a neutral solution is……. (sodium chloride / ammonium chloride / sodium carbonate)
Ans. Sodium chloride