Solution-Class 9-Science-Chapter-5-Acids, Bases and Salts-Maharashtra Board

Ammonium - Ammonium is odd because Ammonium is cation and rest are anions.

Hydrogen chloride is odd because Hydrogen chloride is acid and rest are base.

Acetic acid is odd because Acetic acid is organic acid, others are inorganic acid

Ammonium chloride is odd because it is acidic salt and rest all are neutral salts.

Sodium carbonate is odd because solution of sodium carbonate is basic, others are neutral salt.

Zinc oxide is odd because it is amphoteric in nature and other ions are basic in nature

Crystalline Common salt is odd because on heating, there is no change in color of compound. But in rest of the compounds, there is change in colour, they are crystalline substances contain water of crystallization.

Acetic acid is odd one because acetic acid is weak electrolytes others are strong electrolytes.

When 5o mL water is added to 50 mL solution of copper sulphate, then reversible reaction occurs and the colour change from pale blue to white.  Also the concentration of copper sulphate solution decreases.

• When two drops of Phenolphthalein indicator are added to 10 mL solution of Sodium hydroxide,  then the solution turns light pink in colour
• because the acidic part of phenolphthalein reacts with the base, it forms sodium salt of phenolphthalein which has pink color.
• Phenolphthalein is an indicator used for determining the quantity of base.

When two to three fillings of copper were added to 10ml dilute nitric acid and stirred, it forms copper nitrite and hydrogen gas.

When litmus paper is dipped into 2 mL of dilute HCl solution , then blue litmus paper is turned into red colour and there is no effect on red litmus paper. Again, if the 2 mL of concentrated NaOH solution added in the same solution, same litmus paper is dipped into, then red litmus paper turns into blue colour but there is no effect on blue litmus paper. This is due to the respective properties of blue and red litmus paper with acid and base.

• Bases react only with oxides of non-metal to form salt and water and neutralization reaction take place.
• Magnesium oxide is a base. When Magnesium oxide was added to dilute HCl, it forms magnesium chloride and water, Magnecium chloride is basic in nature it neutralizes acid. MgO_(s)+ 2HCl_(l) = MgCl_2 (aq) + H₂O_(l).
• There is no reaction between MgO and NaOH, because NaOH & MgO both are basic in nature.

When Zinc oxide is added to dilute HCl, it forms zinc chloride and water and neutralization reaction takes place. In this reaction zinc oxide is basic oxide
ZnO +2HCl → ZnCl₂ + H₂O

When zinc oxide was added to dilute NaOH. Zinc oxide reacts with sodium hydroxide and it forms zincate sodium and water. In this reaction zinc oxide is acidic oxide

ZnO + 2NaOH→Na₂ZnO₂ + H₂O

Therefore zinc oxide is an amphoteric oxide because it shows both acidic and basic properties.

Limestone is calcium carbonate. When Dilute HCl was added to limestone, it forms calcium chloride, water and carbon dioxide gas.

2HCl + CaCO₃ → CaCl₂ + CO₂ +H₂O

• When pieces of blue vitriol are heated in a test tube, then crystal structure of blue vitriol broke down to form a colourless powder and water come out.
• This water is called water of crystallization.
• When water is added to the same test tube, then white powder turned into blue colour again.
• This is due to reversible reaction take place from anhydrous salt to hydrous salt and vice-versa.
• All above changes are physical changes.

When a dilute solution of sulfuric acid is electrolysed, gases are produced at both the anode and the cathode electrode.

The gas produced at the cathode burns with a 'pop' sound, when a sample is lit with a lighted splint. This shows that the gas is hydrogen.

2H⁺ +2e^- → H₂

The gas produced at the anode relights a glowing splint dipped into a sample of the gas. This shows that the gas is oxygen.

4OH^- - 4e^- → 2H₂O + O₂

The gases are produced when ions move towards the electrodes.

1) Acidic Oxides: CO₂ (Carbon dioxide), SO₃ (Sulfur trioxide)

2) Basic Oxides: CaO (Calcium oxide), MgO (Magnesium oxide), Na₂O (Sodium oxide), Fe₂O₃ (Ferric oxide)

3) Amphoteric Oxides: ZnO (Zinc oxide), Al₂O₃ (Aluminium oxide),

Atomic number of Sodium (Na) atom is 11.
Electronic configuration is:
Na = 2, 8, 1
So it contains 1 valence electron. In order to achieve the nearest noble gas configuration, it loses one electron to form Sodium ion.
Na⁺ = 2,8

Atomic number of Chlorine(Cl) atom is 17.
Electronic configuration is:
Cl = 2, 8, 7
So it contains 7 valence electron. In order to achieve the nearest noble gas configuration, it gains one electron to form Chloride ion.
Cl^- = 2,8,8
An Ionic bond is formed between sodium ion and chloride ion by complete transfer of electron from sodium to chlorine, due to electrostatic force of attraction, giving rise to ionic compound sodium chloride.

Atomic number of Magnesium atom is 12.
Electronic configuration is :
Mg = 2, 8, 2
So it contains 2 valence electron. In order to achieve the nearest noble gas configuration, it loses two electrons to form Magnesium ion.
Mg²⁺ = 2,8

Atomic number of Chlorine(Cl) atom is 17.
Electronic configuration is :
Cl = 2, 8, 7
So it contains 7 valence electron. In order to achieve the nearest noble gas configuration, it gains one electron to form Chloride ion.
Cl^- = 2,8,8
Due to the electrostatic force of attraction an Ionic bond is formed between Magnesium ion and two Chloride ion by complete transfer of one electron to each Chlorine ion and this results in the formation of magnesium chloride.

(i) HCl  \(\underrightarrow{water}\)   H⁺ + Cl^- Dissociation is large

(ii) NaCl \(\underrightarrow{water}\)   Na⁺  + Cl^-  Dissociation is large

(iii) KOH \(\underrightarrow{water}\)   K⁺ + OH^-    Dissociation is large

(iv)  NH₃  \(\underrightarrow{water}\)  NH₄⁺ + OH^- Dissociation is small

(v) CH₃COOH   \(\underrightarrow{water}\)     CH₃COO^-  + H⁺ Dissociation is small

 (vi) MgCl₂  \(\underrightarrow{water}\)   Mg²⁺ + Cl^-    Dissociation is small

 (vii) CuSO₄  \(\underrightarrow{water}\)  Cu⁺² + SO₄^-2 Dissociation is large

1) 7.3 g HCl in 100 mL solution:
Given: Volume of solution = 100ml =0.1L, Mass of Solute in gram =7.3g

Molecular Formula = HCL

Molecular mass of HCl = 1+35.5=36.5 m

Mass of HCL in Mole (mol)

= Mass of HCL in gram(g)/ Molecular mass(m) = 7.3/36.5 =0.2 mol

Concentration of HCl (g/L)

=Mass of solute (g)/Volume(L) = 7.3g/0.1L = 73 g/L

Concentration of HCL (mol/L)

=Mass of HCL in moles/Volume of HCl in L = 0.2mol/0.1L = 2 mol/L

Answer is 73 g/L & 2 mol/L

Given: Volume of solution = 50ml =0.05L, Mass of NaOH in gram =2g

Molecular Formula = NaOH

Molecular mass of NaOH = 23 +16 + 1 = 40m

Mass of HCL in Mole (mol)

= Mass of NaOH in gram(g)/ Molecular mass(m) = 2/40 =0.05 mol

Concentration of NaOH (g/L)

=Mass of solute (g)/Volume(L)  = 2g/0.05L = 40 g/L

Concentration of NaOH (mol/L)

=Mass of NaOH in moles/Volume of NaOH in L = 0.05mol/0.05L = 1 mol/L

Answer is 40 g/L & 1 mol/L

Given: Volume of solution = 100ml =0.1L, Mass of CH₃COOH in gram =3g

Molecular Formula = CH₃COOH

Molecular mass of CH₃COOH = 2(C)+2(O)+4(H) =2 × 12 + 2 × 16 + 4 × 1 = 60m

Mass of CH₃COOH in Mole (mol)

= Mass of CH₃COOH in gram(g)/ Molecular mass(m) = 3/60 = 0.05 mol

Concentration of CH₃COOH (g/L)

=Mass of solute (g)/Volume(L) = 3g/0.1L = 30 g/L

Concentration of CH₃COOH (mol/L)

= Mass of CH₃COOH(mol)/Volume of CH₃COOH (L)

=0.05mol/0.1L = 0.5 mol/L

Answer is 30 g/L & 0.5 mol/L

Given: Volume of solution = 200ml =0.2L, Mass of CH₃COOH in gram =4.9g

Molecular Formula = H₂SO₄

Molecular mass of H₂SO₄ = 2(H)+1(S)+4(O) = 2 × 1 + 32 + 4 ×16 = 98m

Mass of H₂SO₄ in Mole (mol)

= Mass of H₂SO₄ in gram(g)/ Molecular mass(m)= 4.9/98 = 0.05 mol

Concentration of H₂SO₄ (g/L)

=Mass of solute (g)/Volume(L)  = 4.9g/0.2L = 24.5 g/L

Concentration of H₂SO₄ (mol/L)

= Mass of H₂SO₄ (mol)/Volume of H₂SO₄ (L)

= 0.05mol/0.2L = 0.25 mol/L

Answer is 24.5 g/L & 0.25 mol/L

This is an activity based question in which you are supposed to collect rainwater from different places. If we take samples of rain water from different places, we observe the following results :

• pH of water is less than 7 i.e. near about 6.5, Therefore rain water is acidic in nature.
• Rain water contain some micronutrients which are useful for growth of plant.
• While raining Nitrogen from air dissolves in water to form nitrates, plants get nitrogen from soil in the form of nitrates and fertilizers. This helps plants to grow.
• Rain water mixes in river, as rain water is acidic in nature, it decrease ph value of river water. It is difficult for aquatic animals to survive in this water.

The number of ionizable hydrogen (H⁺) ions obtainable by dissociation of one molecule of an acid is called its basicity
For example :
HCl   ---------> H⁺ + Cl^-
Basicity of HCl is 1.

H₂SO₄ ------> 2H⁺ + SO₄^2-
Basicity of H₂SO₄ is 2.

Based on Basicity acids were classified into different types:
1. Mono-basic acids
2. Di-basic acids
3. Tri-basic acids

1. Mono-basic acids:

Acids, which on ionization produce one hydrogen ion.

Example: HCl, HNO₃ etc.

2. Di-basic acids:

Acids, which on ionization produce two hydrogen ion

Example: H₂SO_4, H₂CO₃ etc.

3. Tri-basic acids:

Acids, which on ionization produce three hydrogen ion

Example: H₃PO₄, H₃PO₃ etc.

Neutralization reaction :

A neutralization reaction is a reaction in which an acid and a base reacts to form water and a salt.

It involves the combination of H⁺ ions and OH^- ions to generate water.

Acid       + Base        →  Salt + Water

HCL(aq) + NaOH(aq) →  NaCl  +    H₂O

H⁺ ions from acid and OH^- ions are formed from base

H⁺ (aq) + OH^- (aq) →   H₂O(l)

H⁺ ions from an acid and OH^- ions from a base to form unionized water, this is called neutralization.

When a solution is neutralized, it means that salts are formed from equal weights of acid and base.

Neutralization reaction has application in daily life:

1) Acidity in digestive system :
An acidic stomach due to eating too much spicy food, can be relieved by taking an antacid. The antacid is alkaline/basic in nature and helps to neutralize the stomach's acidity or you may take magnesium hydroxide(Milk of magnesia) and sodium hydrogen carbonate(Baking soda).

2) Tooth decay :
When we eat food containing sugar, then bacteria present in our mouth break down the sugar to form acids(such as lactic acid). Thus acid is formed in the mouth after digestion. This will lead to the cause of tooth decay. The best way to prevent tooth decay is to clean the mouth after eating food with toothpaste, which is basic in nature. This will result in neutralization of acid by base.

3) Plant growth :
Most of the plants grow best when the pH of the soil is close to 7 that's neural. If the soil is too acidic or too basic (alkaline), the plants grow badly.
The acidic soil is neutralize by treatment with materials like quicklime (calcium oxide) or slaked lime (calcium hydroxide) or chalk(calcium carbonate).
If the soil is too basic, then alkalinity can be reduced by adding decaying organic matter (manure or composite) which contains acidic materials.

Electrolysis of water :
When electric current is passed through water containing a few drops of an acid or a few drops of a base, it dissociates to give H+ ions and OH-ions. Hydrogen gas is formed near the cathode and oxygen gas near the anode. This is called electrolysis of water.

The following equation represents the electrolysis of water :H₂O(l)

In pure water, at the negatively charged cathode, a reduction reaction takes place, with electrons (e⁻) from the cathode being given to hydrogen cations to form hydrogen gas.

Reduction at cathode: 2 H⁺ + 2e⁻ → H₂

On positively charged anode, an oxidation reaction occurs, generating oxygen gas by giving electrons to the anode :

Oxidation at anode: 2 H₂O → O₂(g) + 4 H⁺(aq) + 4e⁻

Overall reaction: 2 H₂O(l) → 2 H₂(g) + O₂(g)

The number of hydrogen molecules produced is thus twice the number of oxygen molecules.  The produced hydrogen gas has therefore twice the volume of the produced oxygen gas. The number of electrons pushed through the water is twice the number of generated hydrogen molecules and four times the number of generated oxygen molecules.

The strength of an acid is measured in terms of the extent of the dissociation of acid in an aqueous solution. The higher H⁺ ion concentration the stronger is the acid.

H⁺ ion does not exist alone H⁺ ion is being unstable, When an acids dissolve in water. The H⁺ ion from acid always goes to the nearest water molecule to form hydronium ion.
HCl(aq)+H₂O(aq)→H₃O⁺(aq)+Cl-(aq)

H₂O + H⁺  → H₃O⁺ ion

• Buttermilk spoils if kept in a copper or brass container because Brass or copper reacts with organic acid.
• Buttermilk contains lactic acid and reacts with brass or copper and poisonous salts formed.
• It is the reaction between acid and metal . This reaction is called as electro chemical reaction..

It forms sodium chloride and water is neutralization reaction.

HCl(l) + NaOH(l) → NaCl(s) + H₂O(l) + Energy

It forms zinc sulphate and hydrogen gas

Zn(s)+ H₂SO₄(l)→ ZnSO₄(s) +H₂ (g)

It forms calcium nitrate and water

CaO(s) + 2HNO₃(l)→ Ca(NO₃)₂ (s)+ H₂O(l)

It forms potassium carbonate and water

KOH(l) + CO₂(g)→ KHCO₃

It forms sodium chloride and carbon dioxide gas.

NaHCO₃(s)+ 2HCl(l)→ NaCl(s) + H₂O (l)+ CO₂