WBBSE Class 9 Physical Science Solutions Chapter 4.4 Acids, Bases and Salts

Detailed explanations in West Bengal Board Class 9 Physical Science Book Solutions Chapter 4.4 Acids, Bases and Salts offer valuable context and analysis.

WBBSE Class 9 Physical Science Chapter 4.4 Question Answer – Acids, Bases and Salts

Very short answer type question

Question 1.
Which element must an acid contain?
Answer:
Hydrogen

Question 2.
The aqueous solution of HCl shows acidic character. Which ion is responsible for it?
Answer:
Hydronium ion (H₃O⁺)

Question 3.
Give the name and formula of anion present in the aqueous solution of bases.
Answer:
Flydroxyl ion (OH^–)

Question 4.
Which indicator is used in the titration of strong acid and weak base?
Answer:
Methyl orange

Question 5.
Name an acid salt.
Answer:
Sodium bisuiphate (NaHSO₄)

Question 6.
Which ions disappear in neutralization?
Answer:
W ions generated by acid and OH^– ions generated by alkali disappear in a neutralization process.

Question 7.
What is an oxide?
Answer:
An oxide is a compound of oxygen formed with another element.

Question 8.
Name a tribasic acid.
Answer:
Phosphoric acid (HPO₄)

Question 9.
Give an example of an organic acid.
Answer:
Formic acid (HCOOH)

Question 10.
Give an example of a normal salt.
Answer:
Sodium chloride (NaCl)

Question 11.
What is the nature of aqueous solution of carbon dioxide?
Answer:
Acidic

Question 12.
What type of salt is this — NaHCO₃?
Answer:
Acidic.

Question 13.
What is the use of methyl orange?
Answer:
As an indicator

Question 14.
What is neutralisation?
Answer:
Neutralisation: It is the process in which acids and alkalis in equivalent quantities in their aqueous solutions react to produce salt and the neutral substance water.

Question 15.
Give an example of a neutral oxide.
Answer:
Carbon monoxide (CO)

Question 16.
What will be the colour of the solution if few drops of phenolphthalein are added in aqueous solution of ammonium hydroxide?
Answer:
Pink colour

Question 17.
What will be the colour of the solution if few drops of phenolphthalein are added in aqueous solution of sodium carbonate?
Answer:
Pink colour

Question 18.
Which Indicator is used in the titration of weak acid and strong base?
Answer:
Phenolphthalein.

Question 19.
What is the nature of ZnO?
Answer:
Amphoteric oxide.

Question 20.
Give an example of an acid which has oxidising property.
Answer:
Nitric acid (HNO₃)

Question 21.
What will be the colour of the solution if few drops of phenolphthalein are added in aqueous solution of sodium hydrogen carbonate?
Answer:
Colourless

Question 22.
Which one is used in vanishing colour— NH₄OH or NaOH?
Answer:
NH₄OH

Question 23.
What is the basicity of CH₃COOH?
Answer:
Basicity of CHCOOH is 1.

Question 24.
What is the acidity of NaOH?
Answer:
Acidity of NaOH is 1.

Question 25.
Give an example of an oxide of metal which is not basic in nature.
Answer:
Mn₃O₄.

Question 26.
Give an example of a double salt.
Answer:
K₂SO₄ ,Al₂(SO₄)₃, 24H₂O (Potassium alum)

Question 27.
How many replaceable hydrogen atoms are present in sulphuric acid?
Answer:
Two replaceable hydrogen atoms are present in sulphuric acid.

Question 28.
Give an example of an organic base.
Answer:
Methylamine (CH₃NH₂)

Question 29.
Give an example of an inorganic gaseous compound which has basic property.
Answer:
Ammonia (NH₃)

Question 30.
What are the colour of methyl red in acidic and alkaline medium?
Answer:
The colour of methyl red in acidic medium is red and that in alkaline medium is yellow.

Question 31.
What is an Indicatlor?
Answer:
An indicator: It is some weak organic acid or base which indicates distinctive colours in acid, alkali and neutral solutions.

Question 32.
Why the farmers add slaked lime in the soil?
Answer:
Farmers add slaked lime (Calcium hydroxide) to reduce acidity of the soil.

Question 33.
What should we take in case of acidity and why?
Answer:
We should take antacid in case of acidity because magnesium hydroxide is present in antacid which neutralises excess HCl produced in the stomatch.

Question 34.
Give one example of basic salt.
Answer:
Basic lead nitrate [Pb(OH)NO₃

Short answer type questions 

Question 1.
What are oxides ? What are the types of oxides?
Answer:
Oxides : Binary compounds of oxygen with any element (metallic and non-metallic) are called oxides.
Types of oxides :

• Acidic oxide
• Basic oxide
• Neutral oxide
• Amphoteric oxide
• Peroxide
• Mixed oxide
• Poly-oxide
• Sub-oxide
• Super-oxide

Question 2.
Define acidic oxide.
Answer:
Acidic oxide : An acidic oxide is an oxide of a non-metal usually. It reacts with an alkali or a base to form salt and water. Example : CO₂, SO₂, P₂O. etc.

Question 3.
Define basic oxide.
Answer:
Basic oxide: A basic oxide is usually an oxide of a metal usually. It reacts with an acid to produce salt and water. Example: CaO, MgO. CuO etc.

Question 4.
Define neutral oxide.
Answer:
Neutral Oxide : The oxides of certain non-metals which neither react with acid nor with base are called neutral oxide. Example : CO, H₂O, NO etc.

Question 5.
Define amphoteric oxide.
Answer:
Amphoteric oxide : The oxides of certain weak electropositive metals which react with both acids and bases to form salts and water are called amphoteric oxides. Example : Al₂O₃, ZnO, PbO etc.

Question 6.
What are acids ?
Answer:
Acids : Ordinarily, an acid is a compound, the molecules of which contain one or more hydrogen atoms replaceable partially or completely, directly or indirectly by a metal or a group of elements behaving like a metal to form salt. Example : HCl, H₂SO₄, HNO₃ etc.

Question 7.
What are bases ?
Answer:
Bases : A base in general is an oxide or hydroxide of a metal and when reacts with an acid produces salt and water. Example : Al₂O₃, Al(OH)₃, CaO etc.

Question 8.
What are alkalis ?
Answer:
Alkalis : Water-soluble hydroxide of metals are called alkalis. Example : NaOH, KOH etc.

Question 9.
What are salts ? What are the different types of salt ?
Answer:
Salt : The replaceable hydrogen atoms in an acid when replaced by metal or basic radical partially or fully then the compound so produced is called salt.
Types of salt:

•  normal salt
• acid salt
• basic salt
• double salt and
• complex salt

Question 10.
Define normal salts.
Answer:
Normal salts : The salts produced by complete displacement of all the replaceable hydrogen atom or atoms present in the molecule of an acid by a metal or a radical acting like metal are called normal salts. Example : NaCl, Na₂SO₄, Na₃PO₄ etc.

Question 11.
Define acid salts or bi-salts.
Answer:
Acid salts or bi-salts : The salts produced by the partial displacement of the replaceable hydrogen atoms present in the molecule of an acid by a metal or a radical acting like metal are known as acid salts or bi-salts. Example : NaHSO₄, NaHCO₃, Na₂HPO₄ etc.

Question 12.
Define basic salt.
Answer:
Basic salt: Salts formed by the partial displacement of oxide or hydroxide of alkalis by an acid is known as basic salt. Example: Pb(OH)Cl, Pb(OH)NO₃ etc.

Question 13.
Define double salt.
Answer:
Double salt : It is formed by the association of two or more normal salts.
Example : K_BSO4, Al₂(SO₄)₃, 24H₂O; (NH₄)₂ SO₄, FeSO₄, 6H₂O etc.

Question 14.
Define complex salt.
Answer:
Complex salt : Salts that dissociate in water to give one simple ion and one complex ion are called complex salts.
Example : K₄[Fe(CN)₆], [Cu(NH₃)₄]SO₄, [Ag(NH₃)2Cl] etc.

Question 15.
What is neutralisation reaction ?
Answer:
The reaction in which equivalent amount of an acid reacts with equivalent amount of a base and therefore the properties of acid and base are completely lost by forming salt and water is called neutralisation reaction.

Question 16.
What do you mean by titration ?
Answer:
Titration : The process by which bases are neutralised with the help of acids or vice-versa is known as titration.

Question 17.
What is an indicator ?
Answer:
The substances which indicate the completion moment or end point of a titration reaction by changing their own colour are known as indicators.
Example : Methyl yellow, Methyl orange.

Question 18.
Which ions disappear in neutralisation ?
Answer:
Ions disappear in neutralisation: H⁺ ions generated by acid and OH^– ions generated by alkali disappear in a neutralisation process.

Question 19.
What is vanishing colour ? How is it prepared ?
Answer:

•  Vanishing colour : It is a coloured solution which becomes colourless on exposure to air for a passage of time.
• Preparation of vanishing colour : It is a dilute solution of ammonia in water with a few drops of phenolpthalein. Its colour is deep pink.

Question 20.
How does vanishing colour act ?
Answer:
Action of vanishing colour : When the pink solution of vanishing colour is spread over a white linen, the linen turns pink. On allowing the pink-coloured wet linen to dry in air, the ammonia from the solution evaporates and therefore the linen regains its original white colour.

Question 21.
Can a vanishing colour be prepared with dilute NaOH solution ?
Answer:
Vanishing colour cannot be prepared with dilute NaOH solution due to the fact that sodium hydroxide (NaOH) does not evaporate.

Question 22.
Why is acid called a proton donor ?
Answer:
Acid is called a proton donor: Acids produce cation (H⁺) in aqueous solution. H⁺ is known as proton. So acid is called a proton donor.

Question 23.
Why is aikali called a proton acceptor ?
Answer:
Alkali is called a proton acceptor: Alkali produces hydroxyl ion (OH^–) in aqueous solution, hydroxyl accepts proton (H⁺) coming from aqueous solution of acid to produce water. So, alkali is called a proton acceptor.

Question 24.
Aqueous solution of HCl turns blue litmus red but HCl vapour does not, why ?
Answer:
Reason: HCl vapour is a covalent compound, so it does not ionises in vapour state. In aqueous solution, HCl produces H₃O⁺ (hydronium ion) and acts as an electrovalent compound which turns blue litmus red.

Question 25.
Sodium carbonate is a neutral salt, but its aqueous solution is alkaline in nature, why ?
Answer:
Reason: Sodium carbonate reacts with water and produces caustic soda which is a strong alkali, and a weak acid carbonic acid. Due to the production of strong alkali, after neutralisation of H⁺, there is excess OH^– (hydroxyl ion) in the solution. So the solution will be alkaline in nature.
Equation : Na₂CO₃ + H₂O → (Na⁺ + OH^–) + H₂CO₃

Question 26.
Why CaH₂ and CH₄ are not acids ?
Answer:
CaH₂ and CH₄ are not acids : Calcium hydride (CaH₂) and methane (CH₄) do not produce H⁺ ions in aqueous solution, so these are not acids, for every acid produces H⁺ ions in aqueous solution.

Broad answer type questions 

Question 1.
What is Arrhenius concept of acid ?
Answer:
Arrhenius concept of acid : According to Arrhenius, a Swedish scientist, an acid is a chemical compound that dissociates in water, producing H⁺ ions (cations) as the only positive ions. H⁺ ion is called proton. So an acid is known as proton donor. But H⁺ (proton) does not remain in free state in solution, it attains stability being attached to a molecule of the solvent. In water solution proton combines with a water molecule to produce hydronium ion (H₃O⁺).
Example:

Question 2.
What is Arrhenius concept of base?
Answer:
Arrhenius concept of base: According to Arrhenius, a base is a chemical compound which produces OH^– ions (hydroxyl ions) as the only anions when they are dissolved in water.
Example:

Question 3.
Acids are hydrogen compounds but all hydrogen compounds are not acids — Explain.
Answer:
Explanation : It is to be noted that any acid contains hydrogen but any compound containing hydrogen is not an acid. A compound containing one or more than one hydrogen atom in its molecule will be termed as acid only when its hydrogen atom or atoms are replaceable by a metal and the product thus obtained must be a salt.

Example : None of the four hydrogen atoms of methane (CH₄) can be replaced by a metal. The metals like sodium, potassium displace hydrogen from water (H₂O) but the product obtained in each case is not a salt. So, methane and water, though they contain hydrogen atoms in their molecules are not acids.

Question 4.
What are the important properties of acids ?
Answer:
Important properties of acids :

• Taste : Generally, the aqueous solutions of acids have a sour taste.
• pH value : pH value of an acid is generally less than 7.
• In aqueous solution, the acids conduct electricity.
• Reactions with metals : The solutions of acids in water react with many metals like zinc, magnesium, iron etc. which are more electropositive than hydrogen with the liberation of hydrogen gas and formation of corresponding salts.
• Reactions with oxides and hydroxides of metals: Acids react with metallic oxides or hydroxides producing salts and water.
• Reactions with carbonates and bicarbonates : Acids are also characterised by their tendency to react with metallic carbonates and bicarbonates evolving carbon dioxide.
• According to Arrhenius theory of electrolytic dissociation, the acids in aqueous solutions produce hydrogen ions as the positive ions or cations (H⁺).
• The aqueous solution of an acid turns blue litmus red.

Question 5.
What are the important properties of alkalis ?
Answer:
Important properties of alkalis :

• Alkalis react vigorously with acids to produce salts and water,
• Their aqueous solution turn red litmus blue.
• The aqueous solutions of alkalis are soapy to touch and conduct electricity.
• The alkalis in aqueous solution ionise to produce hydroxyl ions (OH^–).

Question 6.
State the properties of acids and bases with respect to indicators.
Answer:
Properties of acids with respect to indicators : The aqueous solution of acids turns —

• blue litmus to red.
• orange coloured methyl organge to pinkish red :
• phenolphthalein remains colourless in aqueous solution of an acid.

Properties of bases with respect to indicators : The aqueous solution of bases turns  —

• red litmus to blue.
• orange coloured methyl orange to yellow.
• olourless phenolphthalein solution to pink.

Question 7.
Discuss the role of indicators in case of titration.
Answer:
Uses of indicators in titration reaction : Indicators are able to determine the end-point of a titration reaction. List of some well-known indicators are given below

Indicator		Colour changes in
		Neutralsolution	Acidic solution	Alkaline solution
1.	Litmus	Violet	Red	Blue
2.	Methyl-orange	Orange	Red	Yellow
3.	Phenolphthalein	Colourless	Colourless	Pink

The selection of a suitable indicator to determine the correct end point of a reaction :

• Strong acid and weak base: Methyl orange
• Weak acid and strong base: Phenolphtyalein
• Strong acid and strong base: Any indicator
• Weak acid and weak base: No suitable indicator.

Question 8.
How to ascertain whether a given colourless solution is acidic or alkaline by a simple test?
Answer:
Test: A strip of filter paper is dipped in red litmus solution. As a result, the colour of the paper turns red. The piece of paper is dried and the dry piece of paper is dipped in the given solution. If its colour remains red, the given solution is acidic. But if the colour of the litmus paper turns blue, the given solution is alkaline.

Question 9.
What is basicity of an acid and acidity of a base?
Answer:
Basicity of an acid : Basicity of an acid is expressed by the number of replaceable hydrogen atoms present in each molecule of the acid.
Example: Monobasic acid : HCl, HNO.

(i.e. basicity is 1)
Dibasic acid : H₂
Tribusic acid : H₃PO₄
(i.e. basicity is 3)

Acidity of a base : Acidity of a base is expressed by the number of hydroxyl groups present in each molecule of the base.
Example: Monoacidic base : NaOH, KOH
Diacidic base : Ca(OH)₂, Mg(OH)₂
Triacidic base : Al(OH)₃

Question 10.
All alkalis are bases but all bases are not alkalis – Explain.
Answer:
Explanation : Bases are the oxides or hydroxides of metals and react with acids to produce salts and water. The bases which are soluble in water are known as alkalis. Ferric hydroxide (Fe(OH₃), Zinc hydroxide (Zn(OH₂), Aluminium hydroxide (Al(OH₃), Sodium hydroxide (NaO), Potassium hydroxide (KOH) all are bases but not alkalis. Among them only water soluble metallic hydroxides NaOH and KOH are alkalis. From the above examples of bases and alkalis, it is clear that all alkalis are bases but all bases are not necessarily alkalis.