Publisher | : Santra publication pvt. ltd. |
Book Name | : Madhyamik Physical Science And Environment |
Class | : 9 (Madhyamik) |
Subject | : Physical Science |
Chapter Name | : Acids Bases and Salts |
Table of Contents
ToggleMultiple Choice Questions (MCQ)
[Each of Mark-1]
Question 1
Which one is not an Arrhenius acid?
- HCl
- HF
- HNO3
- C2H2
Answer
C2H2
Explanation
C2H2 is not an Arrhenius acid because it does not produce H+ ions in water. The other three acids ionize in water to produce H+ ions.
Question 2
An acid is a compound
- having hydrogen atom
- having lone pair of electron
- that can donate proton
- that can accept proton
Answer
that can donate a proton
Explanation
An acid is a compound that can donate a proton to another molecule or accept an electron pair, typically having a hydrogen atom.
Question 3
A base is that
- has oxygen atom
- can accept proton
- can donate proton
- is sour in taste
Answer
can accept proton
Explanation
A base is a compound that can accept a proton, typically having an oxygen atom, and has a bitter taste.
Question 4
Which is amphiprotic?
- HCN
- NH3
- NaOH
- H2O
Answer
H2O
Explanation
Amphiprotic refers to a substance that can act as both an acid and a base, meaning it can donate or accept protons.
Question 5
Which one is not a strong acid?
- HNO3
- HCl
- H2SO4
- CH3COOH
Answer
CH3COOH
Explanation
CH3COOH is not a strong acid. HNO3, HCl, and H2SO4 are strong acids that ionize completely in water.
Question 6
Baking soda consists of
- Na2CO3
- H2CO3
- NaHCO3
- CH3COOH
Answer
NaHCO3
Explanation
Baking soda consists of NaHCO3, which is sodium bicarbonate. When heated or reacted with acid, it releases CO2 gas.
Question 7
Baking powder is a mixture of NaHCO3 and
- Vinegar
- CH3COOH
- Oxalic acid
- tartaric acid
Answer
tartaric acid
Explanation
Baking powder is a mixture of NaHCO3 and tartaric acid or a similar acid, which releases CO2 gas when heated.
Question 8
Which one is salt?
- HCl
- NH3
- NaCl
- H2O
Answer
NaCl
Explanation
NaCl (sodium chloride) is a salt, formed from the reaction between an acid and a base. HCl is an acid, NH3 is a base, and H2O is a neutral compound.
Question 9
Which one is a normal salt ?
- Na2SO4
- NaHSO4
- NaHCO3
- Pb(OH)Cl
Answer
Na2SO4
Explanation
Na2SO4 (sodium sulfate) is a normal salt because it is derived from a strong base (NaOH) and a strong acid (H2SO4) and does not have acidic or basic properties. The other compounds are either acidic or basic salts. NaHSO4 (sodium bisulfate) and NaHCO3 (sodium bicarbonate) are acidic salts because they are derived from a weak base (NaHCO3) and a strong acid (H2SO4) or a weak acid (H2CO3) and a strong base (NaOH), respectively. Pb(OH)Cl (lead(II) hydroxychloride) is a basic salt because it is derived from a strong base (NaOH) and a weak acid (HCl).
Question 10
Which one is an acid salt ?
- NaHSO4
- NaCl
- Na2SO4
- Cu(OH)NO3
Answer
NaHSO4
Explanation
NaHSO4 (sodium bisulfate) is an acid salt as it is formed from the partial neutralization of sulfuric acid (H2SO4) with sodium hydroxide (NaOH), resulting in an ion that has acidic properties. NaCl and Na2SO4 are normal salts while Cu(OH)NO3 is a basic salt.
Question 11
Which one is a basic salt?
- Na2SO4
- Na2HPO4
- NaCl
- Pb(OH)Cl
Answer
Pb(OH)Cl
Explanation
Pb(OH)Cl (lead(II) hydroxychloride) is a basic salt as it is derived from a strong base (NaOH) and a weak acid (HCl), resulting in an ion that has basic properties. Na2SO4 and NaCl are normal salts while Na2HPO4 is an acidic salt.
Question 12
Which one is a double salt?
- Ca(OCl)Cl (bleaching powder)
- NaKCO3
- [Cu(NH3)4]SO4
- FeSO4.(NH4)2SO4-6H2O (Mohr’s salt)
Answer
FeSO4.(NH4)2SO4.6H2O (Mohr’s salt)
Explanation
FeSO4.(NH4)2SO4.6H2O (Mohr’s salt) is a double salt that forms a blue-green crystalline compound. NaKCO3 is a mixture of two different salts, while Ca(OCl)Cl (bleaching powder) and [Cu(NH3)4]SO4 are not double salts.
Question 13
pH is defined as
- [H3O+]
- log [H3O+]
- – log [H3O+]
- – [H3O+]
Answer
-log[H3O+]
Explanation
pH is defined as -log[H3O+], where [H3O+] is the concentration of hydronium ions in a solution. It is a measure of the acidity or basicity of a solution, with lower pH values indicating higher acidity and higher pH values indicating higher basicity.
Question 14
In neutral water at 25°C, [H+] in mol/L is
- 107
- 10.7
- 10-7
- 1.0
Answer
10-7
Explanation
In neutral water at 25°C, [H+] (the concentration of hydronium ions) is 10-7 mol/L. This means that the concentration of hydroxide ions is also 10-7 mol/L, resulting in a neutral pH of 7.
Question 15
For an aqueous solution at 25°C, pH + pOH is
- 10
- 7
- 12
- 14
Answer
14
Explanation
For an aqueous solution at 25°C, pH + pOH = 14. This is because pH is defined as -log[H+] and pOH is defined as -log[OH–], and the product of [H+] and [OH–] in water is always 10-14 at 25°C. Therefore, pH + pOH = -log[H+] + (-log[OH–]) = -log([H+][OH–]) = -log(10-14) = 14.
Question 16
pH of pure boiling water is
- 7
- < 7
- 12
- 14
Answer
7
Explanation
The pH of pure boiling water is approximately 7 at standard pressure and temperature. However, it can be slightly acidic or basic due to dissolved gases or impurities.
Question 17
An acid-base indicator is an organic dye which is chemically
- a weak acid
- a weak base
- either a weak acid or a weak base
- a strong acid or a base
Answer
either a weak acid or a weak base
Explanation
An acid-base indicator is an organic dye that is chemically either a weak acid or a weak base. It changes color depending on the pH of the solution it is in, due to the ionization of the acidic or basic functional group in the molecule.
Question 18
Acid turns a blue litmus paper to
- red
- deep violet
- green
- colourless
Answer
red
Explanation
An acid turns a blue litmus paper red. Litmus paper is a pH indicator that changes colour depending on the pH of the solution it is in, with red indicating acidity and blue indicating basicity.
Question 19
Phenolphthalein is a suitable indicator for titration between
- weak acid and weak base
- weak base-strong acid
- strong acid-strong base
- both strong acid-strong base and weak acid-strong base
Answer
both strong acid-strong base and weak acid-strong base
Explanation
Phenolphthalein is a suitable indicator for titration between a weak acid and a strong base or a weak base and a strong acid. It changes color in the pH range of 8.2-10.0, which is suitable for these types of titrations. It is not suitable for titrations between strong acids and strong bases.
Question 20
By acid rain, the pH of the water body
- is reduced
- is increased
- remains the same
- none
Answer
reduced
Explanation
By acid rain, the pH of the water body is reduced. Acid rain is rainwater that has a pH of less than 5.6 due to the presence of sulfur dioxide and nitrogen oxides, which react with water in the atmosphere to form sulfuric acid and nitric acid. When this acidic rainwater enters lakes, rivers, and other water bodies, it can lower their pH and make them more acidic, which can harm aquatic plants and animals.
Answer in one word or in one sentence
[Each of Mark-1]
Question
- What is an acid?
- What is a base ?
- What is a salt ?
- What is a strong acid (or base) ?
- Define pH.
- What is the pH value of neutral water at 25°C.
- What is a neutralization reaction?
- Give example of each: (i) strong acid, (ii) strong base (iii) weak acid (iv) weak base.
- What is an indicator?
- Are two solutions, 1.0 M HCI and 1.0 M CH3COOH, equally strong?
- Do the solutions 1.0 M HCI and 1.0 M CH3COOH have same pH?
- What is ‘titration’?
- On addition of 2 drops of methyl orange, what colour a NaOH solution will develop?
- How many acidic protons are there in each : (i) CH3COOH, (ii) H2SO4 (iii) Na2CO3 (iv) NaHCO3 (v) H2CO3
- What is an amphoteric salt?
Answer
- Acid is a compound that donates a proton.
- A base is a compound that accepts a proton.
- Salt is a compound formed from the reaction of an acid and a base.
- A strong acid (or base) is a substance that completely ionizes in water.
- pH is a measure of the acidity or basicity of a solution.
- pH value of neutral water at 25°C is 7.
- A neutralization reaction is a chemical reaction between an acid and a base that forms salt and water.
- Examples: (i) HCl (ii) NaOH (iii) CH3COOH (iv) NH3
- An indicator is a substance that changes colour depending on the pH of a solution.
- No, they are not equally strong.
- No, they do not have the same pH.
- Titration is a method of determining the concentration of a solution by reacting it with a solution of known concentration.
- NaOH solution will develop a yellow colour with the addition of methyl orange.
- (i) 1 (ii) 2 (iii) 0 (iv) 1 (v) 2
- Amphoteric salt is a salt that can act as both an acid and a base.
Short answer type questions
[Each of Mark-2]
Question 1
Explain how a salt is produced by partial replacement of hydrogen from H2S. Is the salt is an acidic salt on a basic salt ?
Answer
When the hydrogen atoms in H2S are partially replaced with a metal cation, a salt is formed. This salt is generally an acidic salt due to the acidic nature of H2S.
Question 2
Balance the following equation:
- Na2O2 + H2O→ NaOH + O2;
- Cl2+ NaOH → NaCl + NaClO3 + H2O;
- Cu + HNO3 → Cu(NO3)2 + NO2 + H2O.
Answer
- Na2O2 + 2H2O→ 2NaOH + O2;
- Cl2+ 2NaOH → NaCl + NaClO3 + H2O;
- 3Cu + 8HNO3 → 3Cu(NO3)2 + 2NO2 + 4H2O.
Question 3
What is neutralization? Give example.
Answer
Neutralization is a chemical reaction between an acid and a base that produces a salt and water. An example is the reaction between hydrochloric acid and sodium hydroxide to form sodium chloride and water.
Question 4
Give example of a neutral oxide and an acidic oxide made from the same element.
Answer
Carbon monoxide (CO) is a neutral oxide because it does not react with water to form an acid or a base.
Carbon dioxide (CO2), on the other hand, is an acidic oxide because it reacts with water to form carbonic acid.
Question 5
How would you distinguish between solutions of sodium carbonate and solution of sodium bicarbonate by using indicator ?
Answer
A solution of sodium carbonate will turn phenolphthalein pink, indicating a basic solution. A solution of sodium bicarbonate will turn methyl orange yellow, indicating a slightly acidic solution.
Question 6
An acid forms one acid salt and one normal salt. What is the basicity of the acid?
Answer
The basicity of the acid is 2. An acid that forms one acid salt and one normal salt donates two hydrogen ions per molecule. Therefore, its basicity is 2.
Question 7
- NaCl + Water + X (indicator) → Orange colour; X = ?;
- Na2CO3 + Water + Y (indicator) → Reddish violet ; Y = ?
Answer
X = phenolphthalein; Y = methyl orange.
Question 8
State why potassium bicarbonate is called an acidic salt? Give another example of this type.
Answer
Potassium bicarbonate is called an acidic salt because it is formed by the partial neutralization of an acid (carbonic acid) with a weak base (potassium hydroxide), resulting in an ion that has acidic properties. Another example of this type is sodium dihydrogen phosphate (NaH2PO4).
Question 9
Mention at least two points to distinguish between an acid and a base.
Answer
- Acids donate protons while bases accept protons.
- Acids turn blue litmus paper red while bases turn red litmus paper blue.
Question 10
Aqueous solution of CO2 is acidic or basic or neutral ? How would you show that?
Answer
Aqueous solution of CO2 is weakly acidic. This can be shown by adding an indicator such as bromothymol blue, which will turn yellow in an acidic solution, to the CO2 solution and observing the colour change.
Question 11
- Which acid produces brown fumes on heating ?;
- Which gas is evolved by the reaction of common salt with concentrated H2SO4 ?
Answer
The acid that produces brown fumes on heating is nitric acid (HNO3). This is due to the decomposition of the acid into nitrogen dioxide (NO2) gas, which has a brown colour.
The gas evolved by the reaction of common salt (NaCl) with concentrated H2SO4 is hydrogen chloride (HCl) gas. This is due to the reaction between sodium chloride and sulfuric acid to form hydrogen chloride gas and sodium bisulfate (NaHSO4) salt.
Question 12
What is aqua regia ? Mention one use of it.
Answer
Aqua regia is a 1:3 mixture of concentrated nitric and hydrochloric acids that can dissolve noble metals such as gold and platinum. It is used for metal analysis and in the purification of metals.
Question 13
How many gram of HCl will be required to completely neutralize 80 g of NaOH ? (H. = 1, O 16, Na 23, Cl = 35.5)
Answer
The balanced chemical equation for the reaction between HCl and NaOH is:
HCl + NaOH → NaCl + H2O
The molar mass of NaOH is 40 g/mol. Therefore, 80 g of NaOH is equal to 2 moles of NaOH.
The equation shows that 1 mole of HCl reacts with 1 mole of NaOH. Therefore, 2 moles of HCl are required to neutralize 2 moles of NaOH.
The molar mass of HCl is 36.5 g/mol. Therefore, 2 moles of HCl is equal to 73 g of HCl.
Hence, 73 g of HCl will be required to completely neutralize 80 g of NaOH.
Question 14
Write with balanced chemical equation what happens in the reaction of iron with dilute hydrochloric acid.
Answer
The reaction of iron (Fe) with dilute hydrochloric acid (HCl) produces iron chloride (FeCl2) and hydrogen gas (H2).
Fe + 2HCl → FeCl2 + H2
Question 15
Using barium chloride solution, how will you identify which bottle contains H2SO4 out of three bottles containing HCl, H2SO4 and HNO3, respectively?
Answer
To identify which bottle contains H2SO4 using barium chloride solution, we can follow these steps:
- Add a few drops of barium chloride solution to a small amount of each acid in separate test tubes.
- If H2SO4 is present, a white precipitate of barium sulfate (BaSO4) will form in the test tube containing H2SO4.
- The test tube containing HCl or HNO3 will not show any reaction with the barium chloride solution.
Therefore, the bottle containing H2SO4 can be identified by the formation of a white precipitate of barium sulfate in the test tube containing the acid.
Long answer type questions
[Each of Mark-3]
Question 1
H2S cannot be dried by using concentrated H2SO4-explain why with balanced equations.
Answer
H2S cannot be dried by using concentrated H2SO4 because H2SO4 reacts with H2S to form sulfur and water, which can lead to the formation of a highly explosive mixture of sulfur dioxide and hydrogen sulfide. The balanced chemical equation for this reaction is:
H2SO4 + H2S → 2H2O + S
As seen in the equation, the reaction between H2SO4 and H2S leads to the formation of water and elemental sulfur. Therefore, H2SO4 cannot be used to dry H2S gas as it will not remove moisture and can lead to the formation of a hazardous mixture.
Question 2
A glass rod moistened with con. HCl is introduced in a full of gas. White fumes are produced. Identify the gas in the jar. What is the compound giving fume? Give equation.
Answer
The white fumes produced when a glass rod moistened with concentrated HCl is introduced into a jar of gas are due to the formation of hydrochloric acid (HCl) gas. The gas in the jar could be ammonia (NH3), which reacts with HCl gas to form a white smoke of ammonium chloride (NH4Cl) salt. The balanced chemical equation for this reaction is:
NH3 + HCl → NH4Cl
Therefore, the compound giving white fumes is ammonium chloride (NH4Cl), which is formed by the reaction between ammonia (NH3) and hydrochloric acid (HCl).
Question 3
State the Arrhenius concept related to acid and base.
Answer
The Arrhenius concept of acids and bases defines an acid as a substance that dissociates in water to produce hydrogen ions (H+) and a base as a substance that dissociates in water to produce hydroxide ions (OH–). According to this concept, an acid is a substance that increases the concentration of H+ ions in aqueous solution, while a base is a substance that increases the concentration of OH– ions in an aqueous solution.
Question 4
Why is Na2O called a basic oxide but ZnO is called an amphoteric oxide ? Give equations.
Answer
Na2O is called a basic oxide because it reacts with water to form a strong base, sodium hydroxide (NaOH), which increases the pH of the solution. The balanced chemical equation for the reaction between Na2O and water is:
Na2O + H2O → 2NaOH
On the other hand, ZnO is called an amphoteric oxide because it can react as both an acid and a base. It can react with both acids and bases to form salts, and it can also react with water to form both an acidic and basic solution. The balanced chemical equations for the reactions of ZnO with an acid and a base are:
ZnO + 2HCl → ZnCl2 + H2O
ZnO + 2NaOH → Na2ZnO2 + H2O
Question 5
What colour will be produced when methyl orange is added to dilute NaOH solution? What colour will be produced at the neutralization point if this solution is neutralized with dilute HCl?
Answer
When methyl orange is added to dilute NaOH solution, the solution will turn yellow.
At the neutralization point when the NaOH solution is neutralized with dilute HCl, the solution will change its color from yellow to orange. This is because methyl orange changes color at a pH range of 3.1 to 4.4, with a transition from yellow to orange. The point at which the solution changes from yellow to orange indicates that the solution has been neutralized, and the pH is around 7, which is the pH of neutral water.
Question 6
A bottle contains dilute HCl solution, a second bottle contains an aqueous solution of caustic soda and a third bottle contains an aqueous solution of NaCl. With the help of a blue litmus paper only, how would you identify the contents of the three bottles?
Answer
To identify the contents of the three bottles using a blue litmus paper only, the following steps can be followed:
- Take a blue litmus paper and dip it into the solution in the first bottle.
- If the solution in the first bottle is HCl, the blue litmus paper will turn red due to the acidic nature of HCl.
- Take another blue litmus paper and dip it into the solution in the second bottle.
- If the solution in the second bottle is an aqueous solution of caustic soda (NaOH), the blue litmus paper will turn blue due to the basic nature of NaOH.
- Take a third blue litmus paper and dip it into the solution in the third bottle.
- If the solution in the third bottle is an aqueous solution of NaCl, the blue litmus paper will remain blue as NaCl is a neutral salt and does not affect the pH of the solution.
Therefore, by using a blue litmus paper, we can identify the contents of the three bottles as follows: Bottle 1 contains HCl, bottle 2 contains an aqueous solution of caustic soda (NaOH), and bottle 3 contains an aqueous solution of NaCl.
Question 7
Write with a balanced chemical equation what happens when: (i) concentrated nitric acid is heated with copper turnings. (ii) aluminium powder is boiled with a concentrated aqueous solution of sodium hydroxide.
Answer
(i) When concentrated nitric acid is heated with copper turnings, nitrogen dioxide (NO2) gas is evolved along with the formation of copper nitrate (Cu(NO3)2) and water (H2O). The balanced chemical equation for the reaction is:
8HNO3 + 3Cu → 3Cu(NO3)2 + 4H2O + 2NO2
(ii) When aluminium powder is boiled with a concentrated aqueous solution of sodium hydroxide, hydrogen gas (H2) evolves along with the formation of sodium aluminate (NaAlO2) and water (H2O). The balanced chemical equation for the reaction is:
2Al + 2NaOH + 6H2O → 2NaAl(O2H)4 + 3H2
The reaction produces a lot of heat and hydrogen gas is evolved with effervescence.