What is the purpose of passing the gas through lime water in the given setup?

To test for sulphur dioxide gas

Which of the following statements is true about the pH scale?

Higher the hydronium ion concentration, lower is the pH value.

A pH of 7 indicates a strong acid.

As pH increases from 7 to 14, acidic nature increases.

Higher the hydronium ion concentration, lower is the pH value.

The p in pH stands for 'potential'.

Why does dry HCl gas not show acidic behaviour?

It does not dissociate to produce H+ ions in the absence of water.

What happens when copper oxide reacts with dilute hydrochloric acid?

The solution remains colourless.

Assertion (A): Aqueous solutions of acids conduct electricity. Reason (R): Acids produce H+ ions in aqueous solutions which are responsible for the conduction of electricity.

A and R both correct, R explains A

Assertion (A): Non-metallic oxides are acidic in nature. Reason (R): Non-metallic oxides react with bases to form salt and water.

A and R both correct, R explains A

A student performs an experiment where they add a few drops of dilute NaOH solution to a solution containing phenolphthalein, and it turns pink. Then, dilute HCl solution is added drop by drop until the pink colour disappears. What would happen if a few drops of NaOH are added again to this mixture?

The pink colour of phenolphthalein will reappear.

The solution will remain colourless.

The pink colour of phenolphthalein will reappear.

A student accidentally spills a concentrated acid on their hand. What is the immediate and most appropriate first aid action?

Rinse the affected area with plenty of cold water for several minutes.

Apply a strong base like NaOH solution.

Rinse the affected area with plenty of cold water for several minutes.

Cover the area with a dry cloth.

Which two of the following statements are correct regarding the properties of acids?

Acids react with metal carbonates to produce carbon dioxide.

Acids react with metallic oxides to form salt and water.

Which two of the following statements are correct about the properties of bases?

Bases react with non-metallic oxides to form salt and water.

Is this Acids, Bases and Salts quiz free?

Yes, this quiz is completely free for all CBSE Class 10 Science students. No hidden charges or subscriptions required.

How many questions are in the quiz?

The main 'Game Mode' quiz contains 40 multiple-choice questions, divided into easy, medium, and hard difficulty levels. There are also additional sections for NCERT book questions and a monthly test.

Is this quiz based on the NCERT syllabus?

Absolutely! All questions are carefully designed based on the latest NCERT Class 10 Science textbook for the 'Acids, Bases and Salts' chapter, ensuring full syllabus coverage.

Can I check my answers and explanations?

Yes, after attempting each question, you will receive instant feedback on whether your answer is correct, along with a short explanation. You can also view detailed explanations for deeper understanding.

What topics from Acids, Bases and Salts does this quiz cover?

This quiz covers all major topics including indicators, chemical properties of acids and bases, reactions with metals, carbonates, and oxides, pH scale, neutralization, and important salts like baking soda, washing soda, and plaster of Paris.

Can I use this quiz to prepare for my board exams?

Yes, this quiz is an excellent tool for board exam preparation. It helps reinforce concepts, identify weak areas, and practice answering different types of questions, including those from NCERT exercises.

Home › CBSE › Class 10 › Science › Acids, Bases and Salts

CBSE · Class 10 · 🔬 Science · Chapter 2

Acids, Bases and Salts

Acids and BasespH ScaleNeutralization ReactionIndicatorsSalts and their usesChlor-alkali process

This chapter introduces students to the fundamental concepts of acids, bases, and salts, which are crucial for understanding chemical reactions in everyday life. It covers their definitions, chemical properties, reactions with metals, carbonates, and oxides, and the importance of pH in daily phenomena like digestion and acid rain. Students also learn about common salts like sodium hydroxide, bleaching powder, baking soda, and washing soda, and their industrial and domestic uses. Understanding these topics is vital for building a strong foundation in chemistry.

Acids aur Bases ki Chemical Properties

Acids aur Bases ko unki chemical properties se pehchante hain. Indicators ka use karte hain.

1. Indicators

Definition: Substances jo acid ya base ke contact mein aane par apna colour ya smell change karte hain.
Types:
Natural Indicators: Litmus (lichen se milta hai), Turmeric (haldi), Red Cabbage extract.
Litmus: Acidic solution mein red, Basic solution mein blue.
Turmeric: Acidic mein yellow, Basic mein reddish brown.
Red Cabbage: Acidic mein red, Basic mein green.
Synthetic Indicators: Phenolphthalein, Methyl Orange.
Phenolphthalein: Acidic mein colourless, Basic mein pink.
Methyl Orange: Acidic mein red, Basic mein yellow.
Olfactory Indicators: Substances jinki smell (odour) acidic ya basic medium mein change hoti hai. Example: Onion, Vanilla essence, Clove oil.
Onion/Vanilla/Clove oil: Acidic mein odour retains, Basic mein odour disappears.

2. Acids aur Metals ka Reaction

General Reaction: Acid + Metal -> Salt + Hydrogen gas
Example: 2HCl (aq) + Zn (s) -> ZnCl2 (aq) + H2 (g)
Hydrogen gas test: Jab burning candle hydrogen gas ke paas laate hain, toh pop sound produce hoti hai.
[IMAGE: TODO: Reaction of zinc granules with dilute sulphuric acid and testing hydrogen gas by burning]

3. Bases aur Metals ka Reaction

General Reaction: Base + Metal -> Salt + Hydrogen gas (Sab bases metals ke saath react nahi karte)
Example: 2NaOH (aq) + Zn (s) -> Na2ZnO2 (aq) + H2 (g) (Sodium Zincate)

4. Acids aur Metal Carbonates/Hydrogencarbonates ka Reaction

General Reaction: Metal Carbonate/Hydrogencarbonate + Acid -> Salt + Carbon Dioxide + Water
Examples:
Na2CO3 (s) + 2HCl (aq) -> 2NaCl (aq) + H2O (l) + CO2 (g)
NaHCO3 (s) + HCl (aq) -> NaCl (aq) + H2O (l) + CO2 (g)
Carbon Dioxide gas test: CO2 gas ko jab lime water (Ca(OH)2 solution) se pass karte hain, toh solution milky ho jaata hai due to formation of insoluble Calcium Carbonate.
Ca(OH)2 (aq) + CO2 (g) -> CaCO3 (s) + H2O (l) (Milky white precipitate)
Agar excess CO2 pass ki jaaye, toh milkiness disappear ho jaati hai due to formation of soluble Calcium Bicarbonate.
CaCO3 (s) + H2O (l) + CO2 (g) -> Ca(HCO3)2 (aq) (Soluble)
[IMAGE: TODO: Passing carbon dioxide gas through calcium hydroxide solution]

5. Acids aur Bases ka Reaction (Neutralisation Reaction)

Definition: Acid aur Base ke beech ka reaction jisme salt aur water bante hain.
General Reaction: Acid + Base -> Salt + Water
Example: HCl (aq) + NaOH (aq) -> NaCl (aq) + H2O (l)
Yeh ek exothermic reaction hai, heat release hoti hai.

6. Metallic Oxides aur Acids ka Reaction

General Reaction: Metallic Oxide + Acid -> Salt + Water
Example: CuO (s) + 2HCl (aq) -> CuCl2 (aq) + H2O (l)
Metallic oxides basic in nature hote hain, kyuki yeh acids ke saath react karke salt aur water dete hain, jaise bases karte hain.
Copper oxide black hota hai, CuCl2 solution blue-green hota hai.

7. Non-metallic Oxides aur Bases ka Reaction

General Reaction: Non-metallic Oxide + Base -> Salt + Water
Example: CO2 (g) + Ca(OH)2 (aq) -> CaCO3 (s) + H2O (l)
Non-metallic oxides acidic in nature hote hain, kyuki yeh bases ke saath react karke salt aur water dete hain, jaise acids karte hain.

📖Definition

Olfactory Indicators: Wo substances jinki smell (odour) acidic ya basic media mein change ho jaati hai. Example: Vanilla essence, Onion, Clove oil.

📖Definition

Neutralisation Reaction: Acid aur base ke beech ka reaction jisme salt aur water bante hain. Acid + Base -> Salt + Water

💡Tip

Hydrogen gas ko test karne ke liye burning candle use karte hain, 'pop' sound aati hai. Carbon dioxide ko test karne ke liye lime water use karte hain, 'milky' ho jaata hai.

Acids aur Bases mein Common Kya Hai?

Sab acids aur bases mein kuch common properties hoti hain jo unke chemical nature ko define karti hain.

1. Acids mein Common

Sab acids mein Hydrogen (H) hota hai.
Jab acids ko water mein dissolve karte hain, toh woh H+ ions (ya H3O+ ions) produce karte hain.
Conductivity: Acid solutions water mein electricity conduct karte hain kyuki woh ions produce karte hain.
HCl (aq) -> H+ (aq) + Cl- (aq)
H+ + H2O -> H3O+ (Hydronium ion)
Dry HCl gas acidic behaviour show nahi karti: Water ki absence mein H+ ions separate nahi hote, isliye acidic properties show nahi hoti.
[IMAGE: TODO: Acid solution in water conducts electricity]
[IMAGE: TODO: Preparation of HCl gas]

2. Bases mein Common

Sab bases mein Hydroxide (OH) hota hai.
Jab bases ko water mein dissolve karte hain, toh woh OH- ions produce karte hain.
Conductivity: Base solutions water mein electricity conduct karte hain kyuki woh ions produce karte hain.
NaOH (aq) -> Na+ (aq) + OH- (aq)
Alkalis: Wo bases jo water mein soluble hote hain, unhe Alkalis kehte hain. Example: NaOH, KOH, Ca(OH)2.

3. Water ki Presence ka Importance

Acids sirf water ki presence mein H+ ions produce karte hain. Water ki absence mein, woh acidic properties show nahi karte.
Bases sirf water ki presence mein OH- ions produce karte hain.

4. Dilution of Acids aur Bases

Acid ya Base ko water mein dissolve karna ek highly exothermic process hai.
Hamesha acid ko dheere-dheere water mein add karna chahiye, aur continuously stir karte rehna chahiye. Water ko acid mein add nahi karna chahiye, kyuki heat itni zyada generate ho sakti hai ki mixture splash out ho jaaye aur burns cause kare.
Dilution se H+ ya OH- ions ki concentration per unit volume decrease ho jaati hai.

❗Important

H+ ions akele exist nahi karte, woh water molecules ke saath combine karke Hydronium ions (H3O+) banate hain.

📖Definition

Alkalis: Wo bases jo water mein completely soluble hote hain. Example: NaOH, KOH.

🚧Misconception

Acid ko water mein add karte hain, water ko acid mein nahi. Kyuki acid ko water mein add karne se heat slowly dissipate hoti hai, jabki water ko acid mein add karne se sudden aur violent reaction ho sakta hai.

Acid aur Base Solutions Kitne Strong Hain?

Acid ya base ki strength ko measure karne ke liye pH scale ka use karte hain.

1. pH Scale

Definition: Ek scale jo solution mein hydrogen ion concentration (H+) ko measure karti hai. 'p' ka matlab 'potenz' (German mein power).
Range: 0 (highly acidic) se 14 (highly alkaline).
Neutral Solution: pH = 7 (Example: Pure water).
Acidic Solution: pH < 7. Jitna pH kam, utna zyada acidic (H+ concentration zyada).
Basic Solution: pH > 7. Jitna pH zyada, utna zyada basic (OH- concentration zyada).
Universal Indicator: Ek mixture of several indicators jo different pH values par different colours show karta hai.
[IMAGE: TODO: Variation of pH with the change in concentration of H+(aq) and OH–(aq) ions]
[IMAGE: TODO: pH of some common substances shown on a pH paper]

2. Strong Acids aur Weak Acids

Strong Acids: Jo water mein completely dissociate hoke zyada H+ ions produce karte hain. Example: HCl, H2SO4, HNO3.
Weak Acids: Jo water mein partially dissociate hoke kam H+ ions produce karte hain. Example: CH3COOH (Acetic acid), H2CO3 (Carbonic acid).

3. Strong Bases aur Weak Bases

Strong Bases: Jo water mein completely dissociate hoke zyada OH- ions produce karte hain. Example: NaOH, KOH.
Weak Bases: Jo water mein partially dissociate hoke kam OH- ions produce karte hain. Example: Mg(OH)2, NH4OH.

4. pH ki Importance Daily Life mein

Living Organisms: Hamari body 7.0 se 7.8 ke pH range mein work karti hai. Narrow pH range mein hi survive kar sakte hain.
Acid Rain: Jab rainwater ka pH 5.6 se kam ho jaata hai, toh use acid rain kehte hain. Acid rain rivers mein jaakar aquatic life ko harm karti hai.
Soil pH: Plants ko healthy growth ke liye specific pH range ki soil chahiye hoti hai. Farmers apni soil ki pH check karke usko adjust karte hain (acidic soil ko basic substance se, basic soil ko acidic substance se).
Digestive System: Hamare stomach mein HCl produce hota hai jo food digest karta hai. Excess acid se acidity hoti hai, jise antacids (mild bases like Milk of Magnesia, Mg(OH)2) se relieve karte hain.
Tooth Decay: Mouth ka pH 5.5 se kam hone par tooth decay start ho jaata hai. Bacteria sugar ko acid mein convert karte hain. Toothpaste (basic) use karke ise neutralize karte hain.
Self-Defence by Animals aur Plants: Bee sting (acidic) se pain hota hai, jise baking soda (mild base) se relieve karte hain. Wasp sting (basic) ko vinegar (acid) se relieve karte hain. Nettle leaves ke stinging hair methanoic acid release karte hain, jisse pain hota hai, ise dock plant ke leaves rub karke neutralize karte hain.

📖Definition

pH Scale: Hydrogen ion concentration measure karne ka scale. 0-14 tak hota hai. 'p' for 'potenz' (power).

❗Important

pH 7 = Neutral; pH < 7 = Acidic; pH > 7 = Basic. Jitna pH kam, utna zyada acidic. Jitna pH zyada, utna zyada basic.

💡Tip

Daily life mein pH ki applications bahut important hain. Examples ke saath yaad rakho, jaise acid rain, tooth decay, antacids, insect stings.

Salts ke Baare Mein Aur Jaankari

Salts acids aur bases ke neutralisation se bante hain. Unki properties aur uses varied hote hain.

1. Family of Salts

Salts jinmein same positive ya negative radical hota hai, unhe ek family ka kehte hain.
Example: NaCl, Na2SO4 (Sodium salts family); NaCl, KCl (Chloride salts family).

2. pH of Salts

Strong Acid + Strong Base: Neutral salt, pH = 7. Example: NaCl.
Strong Acid + Weak Base: Acidic salt, pH < 7. Example: NH4Cl.
Weak Acid + Strong Base: Basic salt, pH > 7. Example: CH3COONa.

3. Chemicals from Common Salt (NaCl)

Common salt (Sodium Chloride) ek important raw material hai kai useful chemicals ke liye.

a. Sodium Hydroxide (NaOH)

Process: Chlor-alkali process. Brine (aqueous NaCl solution) mein electricity pass karne par NaOH, Chlorine gas, aur Hydrogen gas bante hain.
2NaCl (aq) + 2H2O (l) -> 2NaOH (aq) + Cl2 (g) + H2 (g)
Products aur Uses:
NaOH: Degreasing metals, soaps, detergents, paper making, artificial fibres.
Cl2: Water treatment, PVC, disinfectants, CFCs, pesticides.
H2: Fuels, margarine, ammonia for fertilisers.
[IMAGE: TODO: Important products from the chlor-alkali process]

b. Bleaching Powder (CaOCl2)

Preparation: Dry slaked lime [Ca(OH)2] par Chlorine gas (chlor-alkali process se mili) pass karne par banta hai.
Ca(OH)2 (s) + Cl2 (g) -> CaOCl2 (s) + H2O (l)
Uses:
Textile industry mein cotton aur linen ko bleach karne ke liye.
Wood pulp ko bleach karne ke liye paper factories mein.
Oxidizing agent chemical industries mein.
Drinking water ko germ-free banane ke liye.

c. Baking Soda (Sodium Hydrogencarbonate, NaHCO3)

Preparation: NaCl, CO2, NH3, aur H2O ke reaction se.
NaCl + H2O + CO2 + NH3 -> NH4Cl + NaHCO3
Properties: Mild non-corrosive basic salt.
Uses:
Baking powder ka ingredient (baking powder = baking soda + mild edible acid like tartaric acid). Heating par CO2 release karta hai, jisse bread/cake fluffy bante hain.
NaHCO3 (s) + H+ (from acid) -> CO2 (g) + H2O (l) + Sodium salt of acid
Antacid (alkaline nature ki wajah se excess acid neutralize karta hai).
Soda-acid fire extinguishers mein.

d. Washing Soda (Sodium Carbonate Decahydrate, Na2CO3.10H2O)

Preparation: Baking soda ko heat karke Sodium Carbonate banate hain, fir uska recrystallisation karte hain.
2NaHCO3 (s) -> Na2CO3 (s) + H2O (l) + CO2 (g)
Na2CO3 (s) + 10H2O (l) -> Na2CO3.10H2O (s)
Uses:
Glass, soap, aur paper industries mein.
Sodium compounds jaise Borax ke manufacture mein.
Cleaning agent for domestic purposes.
Water ki permanent hardness remove karne ke liye.

4. Water of Crystallisation

Definition: Salts ke crystals mein fixed number of water molecules present hote hain, unhe water of crystallisation kehte hain.
Example: Copper Sulphate crystals (CuSO4.5H2O) blue hote hain. Heat karne par water lose karte hain aur white anhydrous CuSO4 bante hain. Water add karne par blue colour restore ho jaata hai.
[IMAGE: TODO: Removing water of crystallisation]
Hydrated Salts: Jin salts mein water of crystallisation hota hai. Example: CuSO4.5H2O, Na2CO3.10H2O, CaSO4.2H2O (Gypsum).

5. Plaster of Paris (POP, Calcium Sulphate Hemihydrate, CaSO4.1/2H2O)

Preparation: Gypsum (CaSO4.2H2O) ko 373 K par heat karne par water molecules lose karta hai.
CaSO4.2H2O (s) (Gypsum) --(Heat to 373 K)--> CaSO4.1/2H2O (s) (POP) + 1 1/2 H2O (l)
Properties: White powder jo water ke saath mix karne par hard solid mass ban jaata hai.
CaSO4.1/2H2O + 1 1/2 H2O -> CaSO4.2H2O (Gypsum)
Uses:
Doctors fractured bones ko support karne ke liye.
Toys, decorative materials banane ke liye.
Walls aur ceilings ko smooth karne ke liye.
Fire-proofing material ke roop mein.

📖Definition

Water of Crystallisation: Fixed number of water molecules jo ek salt ke formula unit mein present hote hain.

❗Important

Chlor-alkali process se NaOH, Cl2, aur H2 milte hain. Har product ka apna use hai.

💡Tip

Baking soda aur Washing soda ki preparation, properties aur uses mein difference yaad rakho. Chemical formulae aur reactions bhi important hain.

Easy (15)

Which of the following is an olfactory indicator?
- Litmus paper
- Turmeric
- Vanilla essence (correct)
- Phenolphthalein
Why: Vanilla essence is an olfactory indicator as its odour changes in acidic or basic solutions.
Acids turn blue litmus paper to which colour?
- Green
- Red (correct)
- Yellow
- No change
Why: Acids are known to turn blue litmus paper red.
Which gas is typically produced when an acid reacts with a metal?
- Oxygen
- Carbon dioxide
- Hydrogen (correct)
- Nitrogen
Why: Acids react with metals to produce hydrogen gas and a salt.
What is the pH of a neutral solution?
- 0
- 7 (correct)
- 14
- Less than 7
Why: A neutral solution, like pure water, has a pH of exactly 7.
Which of the following is a strong acid?
- Acetic acid (CH3COOH)
- Lactic acid
- Hydrochloric acid (HCl) (correct)
- Citric acid
Why: Hydrochloric acid (HCl) is a strong acid, unlike the others which are weak organic acids.
What is the chemical formula for sodium hydroxide?
- NaCl
- Na2CO3
- NaOH (correct)
- NaHCO3
Why: NaOH is the chemical formula for sodium hydroxide, a strong base.
Which of the following is used as an antacid?
- Sodium chloride
- Sodium hydrogencarbonate (correct)
- Calcium sulphate
- Copper sulphate
Why: Sodium hydrogencarbonate (baking soda) is a common ingredient in antacids.
What is the common name for calcium oxychloride (CaOCl2)?
- Washing soda
- Baking soda
- Bleaching powder (correct)
- Plaster of Paris
Why: Calcium oxychloride (CaOCl2) is commonly known as bleaching powder.
True or False: All bases are soluble in water.
Why: Only bases that are soluble in water are called alkalis; not all bases are soluble.
True or False: The reaction between an acid and a base is called a neutralization reaction.
Why: The reaction of an acid with a base to form salt and water is indeed called neutralization.
True or False: A solution with a pH of 2 is less acidic than a solution with a pH of 5.
Why: A pH of 2 indicates a stronger acid than a pH of 5.
Acids produce _______ ions in aqueous solutions.
Why: Acids produce H+ ions (or hydronium ions, H3O+) in water.
The process of dissolving an acid or a base in water is highly ______.
Why: Dissolving acids or bases in water is an exothermic process, releasing heat.
Identify the gas being tested in the diagram.
- Oxygen
- Carbon dioxide
- Hydrogen (correct)
- Sulphur dioxide
Why: The pop sound test with a burning candle confirms the presence of hydrogen gas.
What is the purpose of passing the gas through lime water in the given setup?
- To test for hydrogen gas
- To test for oxygen gas
- To test for carbon dioxide gas (correct)
- To test for sulphur dioxide gas
Why: Lime water is used to detect carbon dioxide gas, which turns it milky.

Medium (15)

Which of the following statements is true about the pH scale?
- A pH of 7 indicates a strong acid.
- As pH increases from 7 to 14, acidic nature increases.
- Higher the hydronium ion concentration, lower is the pH value. (correct)
- The p in pH stands for 'potential'.
Why: Lower pH values correspond to higher concentrations of hydronium ions, indicating stronger acidity.
When dilute hydrochloric acid is added to sodium carbonate, which gas is produced?
- Hydrogen
- Oxygen
- Carbon dioxide (correct)
- Chlorine
Why: Acids react with metal carbonates to produce carbon dioxide gas, salt, and water.
Why does dry HCl gas not show acidic behaviour?
- It is a covalent compound.
- It does not contain hydrogen.
- It does not dissociate to produce H+ ions in the absence of water. (correct)
- It is a strong base.
Why: Acids show acidic properties by releasing H+ ions, which requires the presence of water.
What happens when copper oxide reacts with dilute hydrochloric acid?
- A colourless gas is produced.
- The solution turns blue-green. (correct)
- A white precipitate is formed.
- The solution remains colourless.
Why: Copper oxide reacts with HCl to form copper(II) chloride, which gives a blue-green colour.
Match the following natural sources with the acids they contain:
Why: Vinegar contains acetic acid, lemon contains citric acid, tamarind contains tartaric acid, and ant sting contains methanoic acid.
Match the following salts with their nature based on the strength of their parent acid and base:
Why: NaCl is neutral (strong acid + strong base), NH4Cl is acidic (strong acid + weak base), and Na2CO3 is basic (weak acid + strong base).
Match the following chemicals with their primary uses:
Why: Sodium hydroxide for soap, bleaching powder for disinfection, baking soda as antacid, and washing soda for water hardness removal.
Match the following processes with the products formed:
Why: Chlor-alkali yields NaOH, Cl2, H2; chlorine on slaked lime yields bleaching powder; heating gypsum yields Plaster of Paris.
What is the chemical name of baking soda?
Why: Baking soda's chemical name is sodium hydrogencarbonate (NaHCO3).
What is the fixed number of water molecules present in one formula unit of a salt called?
Why: The fixed water molecules in a salt's formula unit are called water of crystallisation.
What is the name of the process by which electricity is passed through an aqueous solution of sodium chloride to form sodium hydroxide?
Why: The electrolysis of brine to produce NaOH, Cl2, and H2 is called the chlor-alkali process.
Arrange the following substances in increasing order of their pH values: Lemon juice, Pure water, Sodium hydroxide solution, Gastric juice.
Why: The order from lowest to highest pH is Gastric juice (acidic), Lemon juice (acidic), Pure water (neutral), Sodium hydroxide solution (basic).
Arrange the following steps in the correct order for testing hydrogen gas using the setup shown in Fig 2.1:
Why: The correct sequence involves generating the gas, trapping it in soap bubbles, and then testing with a burning candle.
In the circuit shown, which solution would cause the bulb to glow brightly?
- Glucose solution
- Alcohol solution
- Dilute HCl solution (correct)
- Distilled water
Why: Dilute HCl solution produces ions, allowing it to conduct electricity and make the bulb glow.
What does the warning sign in the image indicate?
- Flammable substance
- Corrosive substance (correct)
- Toxic substance
- Radioactive substance
Why: The warning sign depicts a hand being corroded, indicating a corrosive substance.

Hard (10)

Assertion (A): Aqueous solutions of acids conduct electricity. Reason (R): Acids produce H+ ions in aqueous solutions which are responsible for the conduction of electricity.
Why: Acids conduct electricity because they dissociate into ions (H+), and these ions carry the charge.
Assertion (A): When a few drops of phenolphthalein are added to a dilute solution of sodium hydroxide, a pink colour is produced. Reason (R): Phenolphthalein is a basic indicator.
Why: Phenolphthalein turns pink in basic solutions, but it is an acid-base indicator, not a basic indicator itself.
Assertion (A): Non-metallic oxides are acidic in nature. Reason (R): Non-metallic oxides react with bases to form salt and water.
Why: Non-metallic oxides are acidic because they react with bases to form salt and water, similar to how acids react.
A student performs an experiment where they add a few drops of dilute NaOH solution to a solution containing phenolphthalein, and it turns pink. Then, dilute HCl solution is added drop by drop until the pink colour disappears. What would happen if a few drops of NaOH are added again to this mixture?
- The solution will remain colourless.
- The solution will turn blue.
- The pink colour of phenolphthalein will reappear. (correct)
- A precipitate will form.
Why: Adding NaOH again will make the solution basic, causing phenolphthalein to turn pink again.
A farmer observes that the plants in his field are not growing well. He tests the soil and finds its pH to be 4.5. Which of the following substances would be most suitable to add to the soil to improve plant growth?
- Sulphuric acid
- Slaked lime [Ca(OH)2] (correct)
- Common salt (NaCl)
- Vinegar
Why: Slaked lime is a base that can neutralize the acidic soil and raise its pH.
A student accidentally spills a concentrated acid on their hand. What is the immediate and most appropriate first aid action?
- Apply a strong base like NaOH solution.
- Apply a paste of baking soda.
- Rinse the affected area with plenty of cold water for several minutes. (correct)
- Cover the area with a dry cloth.
Why: Immediate and thorough rinsing with water is crucial to dilute the acid and minimize damage.
Observe the pH scale. Which range represents solutions that are strongly basic?
- 0-3
- 4-6
- 7
- 11-14 (correct)
Why: A pH range of 11-14 indicates strongly basic (alkaline) solutions.
In the chlor-alkali process shown, which product is collected at the anode?
- Hydrogen gas
- Chlorine gas (correct)
- Sodium hydroxide solution
- Brine
Why: During the chlor-alkali process, chlorine gas is produced at the anode.
Which two of the following statements are correct regarding the properties of acids?
- Acids turn red litmus blue.
- Acids react with metal carbonates to produce carbon dioxide. (correct)
- Acids have a bitter taste.
- Acids react with metallic oxides to form salt and water. (correct)
Why: Acids react with metal carbonates to produce CO2 and with metallic oxides to form salt and water.
Which two of the following statements are correct about the properties of bases?
- Bases turn blue litmus red.
- Bases have a soapy touch. (correct)
- Bases react with non-metallic oxides to form salt and water. (correct)
- All bases are strong alkalis.
Why: Bases feel soapy and react with non-metallic oxides, but not all bases are strong alkalis.