Chapter-5 Acids, bases and salts (exampler)

1.What happens when an acid solution and a base solution are combined in a test tube?

(i) The solution's temperature rises.

(ii) The solution's temperature drops.

(iii) The solution's temperature stays constant.

(iv) Salt production occurs. 

(a) (i) only

(b) (i) and (iii)

(c) (ii) and (iii)

(d) (i) and (iv)

Expanation:

The correct option is (b) (i) and (iii). In a test tube, a reaction known as neutralisation occurs when an acid solution and a base solution are combined. This reaction produces salt and water. The temperature of the solution rises as a result of the release of energy from this reaction in the form of heat. However, as the acid and base neutralise one another, the pH of the solution approaches neutral, which means that after an initial rise in temperature brought on by the heat of neutralisation, the solution's temperature essentially stays the same. Therefore, option (i) and (iii) are both correct. Option (ii) is incorrect because the temperature of the solution increases, not decreases. Option (iv) is also correct as salt formation takes place during neutralization.


2. The red litmus solution in an aqueous solution turns blue. Which of the following solutions would undo the change if added excessively?

(a)Baking soda

(b) Lime

(c) a solution of ammonium hydroxide

(d) Acid hydrochloric

Explanation:

The correct answer is (d) Hydrochloric acid.

An aqueous solution that turns red litmus solution blue is a basic solution. The excess addition of an acid can neutralize the basic solution and reverse the change. Among the options given, only Hydrochloric acid is an acid. Baking powder and lime are bases, while ammonium hydroxide solution is also a base (although a weaker one than the other two options). Therefore, adding Hydrochloric acid to the basic solution will neutralize it and reverse the change, turning the blue litmus back to red.


 3. On a humid day, the hydrogen chloride gas is often prepared by passing it through a guard tube containing calcium chloride. The calcium chloride used in the guard tube serves the following purposes: (a) absorbing the evolved gas; (b) moistening the gas; (c) absorbing moisture from the gas; and (d) absorbing Cl- ions from the generated gas.

Explanation:

The correct option is (c) absorb moisture from the gas.During the preparation of hydrogen chloride gas on a humid day, the gas may contain moisture or water vapor. Passing this gas through a guard tube containing calcium chloride helps to remove the moisture from the gas. Calcium chloride is a highly hygroscopic substance, which means that it has a strong affinity for water molecules and can absorb them from the surrounding environment. When the moist hydrogen chloride gas is passed through the guard tube containing calcium chloride, the calcium chloride absorbs the moisture from the gas, leaving behind dry hydrogen chloride gas. Therefore, option (c) is the correct answer. Option (a) and (d) are incorrect because calcium chloride does not absorb the hydrogen chloride gas or Cl- ions from it. Option (b) is also incorrect because calcium chloride does not moisten the gas but rather removes moisture from it.


4. Which of the following salts doesn't have crystallisation water in it?

(a)Blue vitriol, 

(b)baking soda, 

(c)washing soda, 

(d)gypsum, and 

(d)blue vitriol

Explanation:

The correct answer is (d) Gypsum.

Water of crystallization refers to the water molecules that are chemically bound to a salt in a definite ratio in a crystalline solid form. Among the options given, blue vitriol, baking soda, and washing soda all contain water of crystallization. However, gypsum does not contain water of crystallization. Gypsum is a naturally occurring mineral and the main component of plaster of Paris. Its chemical formula is CaSO4·2H2O, which means that it contains two water molecules per formula unit. However, these water molecules are not present as water of crystallization in the crystal lattice of gypsum. Instead, they are physically adsorbed onto the surface of the crystal, and can be driven off upon heating without affecting the crystal structure. Therefore, option (d) is the correct answer.


5. Because it is a salt of

 (a) a strong acid and a strong base, sodium carbonate is a basic salt.

(b) Weak bases and acids

(c) powerful acid and feeble base

(d) a strong base and a weak acid

Explanation:

Because it is a salt of (d) weak acid and strong base, sodium carbonate is a basic salt.Carbonic acid (H2CO3) and sodium hydroxide combine to form sodium carbonate (NaOH). Whereas sodium hydroxide is a powerful base, carbonic acid is a weak acid. Bicarbonate ion (HCO3-), a weak base, is the conjugate base of carbonic acid. There are no acidic or basic characteristics in the sodium ion (Na+). When sodium carbonate is dissolved in water, it goes through a process called hydrolysis in which it combines with the water to create an alkaline solution. In this instance, sodium carbonate is hydrolyzed to sodium hydroxide and bicarbonate ions. Water totally dissociates sodium hydroxide, a strong base, while bicarbonate ions, a weak base, only partially dissociate. Hence, option (d) is the correct answer.


6. The phosphate of calcium is found in tooth enamel. It is (a) basic (b) acidic (c) neutral (d) amphoteric in nature.

Explanation:

The correct answer is (d) amphoteric. Calcium phosphate is the main inorganic component of tooth enamel, which is the hard, outer layer of teeth that protects the underlying dentin and pulp. Its chemical formula is Ca3(PO4)2, and it is an ionic compound consisting of calcium cations (Ca2+) and phosphate anions (PO43-). Calcium phosphate is amphoteric, which means that it can act as both an acid and a base. In acidic environments, calcium phosphate can act as a base and react with hydrogen ions (H+) to form phosphoric acid (H3PO4) and calcium ions (Ca2+).

Ca3(PO4)2 + 6H+ → 2H3PO4 + 3Ca2+

In basic environments, calcium phosphate can act as an acid and react with hydroxide ions (OH-) to form calcium ions and phosphate ions (PO43-).

Ca3(PO4)2 + 6OH- → 2PO43- + 3Ca2+ + 6H2O

In the neutral pH range, calcium phosphate is relatively insoluble and does not undergo significant acid-base reactions. Therefore, option (d) is the correct answer.



7. Water and soil are combined, then allowed to settle. The pH paper turns orange-yellow when exposed to the clear supernatant solution. Which of the following causes this pH paper's colour to turn greenish-blue? 

(a) Lemon juice

(b) Vinegar

(c) Common salt

(d) An antacid

Explanation:

The pH paper turning yellowish-orange indicates that the soil sample dissolved in water is acidic. To change the color of the pH paper to greenish-blue, we need to add a basic substance to the solution. Among the options given, (d) an antacid is likely to change the color of the pH paper to greenish-blue. Antacids are basic substances that are used to neutralize excess stomach acid, and they typically contain compounds like calcium carbonate or magnesium hydroxide. When an antacid is added to the acidic solution, it will react with the acid and form a salt and water, which will make the solution less acidic and more basic. As a result, the pH paper will turn greenish-blue. On the other hand, lemon juice and vinegar are acidic substances that would make the solution more acidic and deepen the yellowish-orange color of the pH paper. Common salt is a neutral substance and would not have any effect on the pH of the solution, so it would not change the color of the pH paper. Therefore, option (d) is the correct answer.


8. Which of the following gives the correct increasing order of acidic strength

  1. Water < Acetic acid < Hydrochloric acid

  2. Water < Hydrochloric acid< Acetic acid

  3. Acetic acid< Water < Hydrochloric acid

  4. Hydrochloric acid< Water<Acetic acid

Explanation:

The correct order of increasing acidic strength among the given options is:

Water < Acetic acid < Hydrochloric acid

In this order, water is neutral with a pH of 7, while acetic acid and hydrochloric acid are both acidic with pH values less than 7. Among the two acidic substances, acetic acid is a weak acid, while hydrochloric acid is a strong acid. A weak acid is one that does not completely dissociate into its ions in solution and has a lower tendency to donate protons (H+) compared to a strong acid. Hydrochloric acid, being a strong acid, completely dissociates into its ions in solution and has a higher tendency to donate protons. Therefore, hydrochloric acid is a stronger acid than acetic acid. Hence, the correct option is 1. Water < Acetic acid < Hydrochloric acid.


9.What should be done if a student's hand accidently gets a few drops of strong acid on it

(a)Use a saline solution to wash the affected area. (b) Wash the affected area promptly with lots of water and apply a paste of sodium hydrogen carbonate. (c) Following washing with plenty of water, apply a solution of sodium hydroxide. (d) Neutralize the acid with a strong alkali.

Explanation:

If a few drops of concentrated acid accidentally spill over the hand of a student, the following steps should be taken: (b) Wash the hand immediately with plenty of water and apply a paste of sodium hydrogen carbonate. The affected area should be washed immediately and thoroughly with plenty of water to remove the acid from the skin. The affected area should be washed for at least 15-20 minutes with running water to completely remove the acid. After washing, a paste of sodium hydrogen carbonate (baking soda) should be applied to the affected area. Sodium hydrogen carbonate is a weak base and can neutralize the acid, thereby preventing further damage to the skin. The paste should be kept on the affected area for some time and then washed off with water. Option (a) washing with saline solution, (c) applying a solution of sodium hydroxide, and (d) neutralizing the acid with a strong alkali are not recommended. Saline solution does not neutralize the acid, and sodium hydroxide is a strong base that can cause further damage to the skin. Neutralizing the acid with a strong alkali can be dangerous as it can generate heat and cause further burns. Therefore, washing with water and applying a paste of sodium hydrogen carbonate is the best course of action

.

10. When sodium hydrogen carbonate is combined with acetic acid, a gas is created. Which of the following claims about the gas' evolution is accurate?

(i) The lime water becomes milky (ii) It puts out a splinter that is on fire (iii) It dissolves in a sodium hydroxide solution (iv) It smells strongly

 (a) (i)(ii), and (iii), (b) (i) (ii), and (iii), (c) (ii), (iii), and (iv), and (d) (i) and (iv).

Explanation:

When sodium hydrogen carbonate (baking soda) is added to acetic acid, carbon dioxide gas is evolved. The following statements are true about the gas evolved:

(i) It turns lime water milky: Yes, carbon dioxide gas turns lime water milky due to the formation of calcium carbonate.

(ii) It extinguishes a burning splinter: Yes, carbon dioxide gas extinguishes a burning splinter as it does not support combustion.

No, carbon dioxide gas does not dissolve in a solution of sodium hydroxide. (iii) It dissolves in a sodium hydroxide solution.

(iv) It has a pungent odour: No, carbon dioxide gas is odorless and colorless.

Therefore, the correct option is (a) (i) and (ii).

11. In addition to being used in cooking, regular salt can serve as the base for the following:

(i) washing soda

(ii) bleaching powder

(iii) baking soda

(iv) slaked lime

(a) (i) and (ii)

(b) (i), (ii) and (iv)

(c) (i) and (iii)

(d) (i), (iii) and (iv)

Explanation:

Common salt (sodium chloride) can be used as a raw material for making the following compounds:


(i) Washing soda (sodium carbonate): Sodium chloride is electrolyzed to form sodium hydroxide, which is further reacted with carbon dioxide to form sodium carbonate (washing soda).


(ii) Bleaching powder (calcium hypochlorite): Sodium chloride is electrolyzed to form chlorine gas, which is reacted with slaked lime (calcium hydroxide) to form bleaching powder (calcium hypochlorite).


(iii) Baking soda (sodium bicarbonate): Sodium chloride is electrolyzed to form sodium hydroxide, which is further reacted with carbon dioxide to form sodium bicarbonate (baking soda).


(iv) Slaked lime (calcium hydroxide): Sodium chloride is not used as a raw material for making slaked lime.

Therefore, the correct option is (c) (i) and (iii).



12. Baking powder contains sodium hydrogen carbonate as one of its ingredients, along with the following acids: 

(a) hydrochloric acid

(b) tartaric acid

(c) acetic acid

(d) sulphuric acid

Explanation:

The other constituent of baking powder is usually an acid, which reacts with sodium hydrogen carbonate (baking soda) to produce carbon dioxide gas, which causes the dough or batter to rise.

Out of the given options, the acid that is commonly used in baking powder is tartaric acid (option b). Tartaric acid is a weak organic acid that reacts with baking soda in the presence of water to release carbon dioxide gas. This reaction helps in making the baked products soft and fluffy.

Therefore, the correct option is (b) tartaric acid.


13. We are recommended to brush our teeth frequently to prevent tooth decay. The typical toothpaste's composition is

(a) acidic

(b) neutral

(c) basic

(d) corrosive

Explanation:

Toothpaste is generally slightly basic (alkaline) in nature to help neutralize the acids produced by the bacteria in our mouth, which can erode the tooth enamel and cause tooth decay. The alkaline nature of toothpaste helps to maintain the pH balance in the mouth, making it less conducive for the growth of acid-producing bacteria.

Therefore, the correct answer is (c) basic.


 14. Which of the following statements concerning an acid and base aqueous solution is true?

I The acid is stronger the higher the pH.

(ii) The acid is weaker the higher the pH.

(iii) Stronger the base, lower the pH

(iv) weaker the base, the lower the pH

  1. I and IIII; B) II and IIII; C) I and IIV; D) II and (iv)

Explanation:

The solution is (d) (ii), and (iv)

On a PH scale, acids are defined as substances with a PH below 7, where a lower PH indicates a stronger acid, and bases are defined as substances with a PH above 7. Acidity will be stronger the higher the PH.


15. The gastric juices that are expelled during digestion have a pH of (a) less than 7, (b) more than 7, (c), equal to 7, (d) equal to 0.

  1. I and IIII; B) II and IIII; C) I and IIV; D) II and (iv)

Explanation:

The solution is (d) (ii), and (iv)

On a PH scale, acids are defined as substances with a PH below 7, where a lower PH indicates a stronger acid, and bases are defined as substances with a PH above 7. Acidity will be stronger the higher the PH  The pH of gastric juices released during digestion is less than 7, typically between 1.5 to 3.5. So, the correct option is (a) less than 7.


16. Which of the following happens when some acid is put to some water?

(i) Ionisation

(ii) Neutralisation

(iii) Dilution

(iv) Salt formation

(a) (i) and (ii)

(b) (i) and (iii)

(c) (ii) and (iii)

(d) (ii) and (iv)

Explanation:

The correct option is (a) (i) and (ii).

When a small amount of acid is added to water, the following phenomena occur:

(i) Ionisation: The acid molecules ionize into hydrogen ions (H+) and negatively charged ions (anions).

(ii) Neutralisation: The hydrogen ions (H+) react with the hydroxide ions (OH-) present in water to form water molecules (H2O), thereby decreasing the concentration of H+ ions and increasing the pH of the solution.

Therefore, option (a) (i) and (ii) is the correct answer.



17. Which of the following can a student who is blind use as an acid-base indicator?

(a) Litmus

(b) Turmeric

(c) Vanilla essence

(d) Petunia leaves

Explanation:

Petunia leaves can be used as an acid-base indicator by visually impaired students. When the petunia flowers are crushed, their petals release anthocyanin pigments that change colour depending on the pH of the solution. In acidic solutions, the petals turn red, while in alkaline solutions, they turn blue or violet. Therefore, visually impaired students can use petunia leaves to detect the acidity or alkalinity of a solution.


18. Which of the following materials won't release carbon dioxide when exposed to weak acid? 

(a) Marble

(b) Limestone

(c) Baking soda

(d) Lime

Explanation:

The correct answer is (d) Lime.

Lime or calcium oxide (CaO) is a basic oxide and does not react with dilute acid to produce carbon dioxide. The reaction of dilute acid with limestone (CaCO3), marble (CaCO3), and baking soda (NaHCO3) produces carbon dioxide gas.



19. That whatever follows is acidic. 

(a) Lime juice

(b) Human blood

(c) Lime water

(d) Antacid

Explanation:

(a) Lime juice is acidic because it contains citric acid and ascorbic acid which are weak acids.

(b) Human blood is slightly basic with a pH range of 7.35-7.45.

(c) Lime water is basic in nature because it is a solution of calcium hydroxide which is an alkali.

(d) Antacid is a basic substance used to neutralize excess stomach acid and provide relief from indigestion and heartburn. 



20. The equipment shown in Figure 2.1 was set up to illustrate electrical conductivity across an electrolyte. Which one or more of the following statements is true?

1. Because the electrolyte is not acidic, the bulb will not glow.

2. Because NaOH is a powerful base and provides ions for conduction, the bulb will glow.

3. The circuit is not complete, so the bulb won't light up.

4. The type of electrolytic solution solely determines whether a bulb will glow. 

(a) (i) and (iii)

(b) (ii) and (iv)

(c) (ii) only

(d) (iv) only

demonstrate electrical conductivity through an electrolyte

Explanation:

Option (c) (ii) only is correct.

Explanation:In the given apparatus, NaOH is an electrolyte that ionizes in water to produce sodium ions (Na+) and hydroxide ions (OH-). Since NaOH is a strong base, it furnishes a large number of ions for conduction. Therefore, the bulb in the circuit will glow due to the flow of current through the electrolyte solution. Option (i) is incorrect because the conductivity of the electrolyte solution does not depend on whether it is acidic or basic. Option (iii) is incorrect because the circuit is complete, as there is a continuous path for the flow of electric current. Option (iv) is incorrect because the conductivity of the electrolyte solution depends on its ability to furnish ions for conduction, which is determined by the nature of the electrolyte.



21. Which one of the following processes dissolves gold? 

(a) Hydrochloric acid

(b) Sulphuric acid

(c) Nitric acid

(d) Aqua regia

Explanation:

Aqua regia is used for the dissolution of gold. It is a mixture of hydrochloric acid and nitric acid in a ratio of 3:1. This mixture is able to dissolve gold due to the presence of nitric acid, which can oxidize the gold to form gold ions (Au3+), and the presence of hydrochloric acid, which can react with the gold ions to form soluble chloride complexes. The use of aqua regia is necessary because gold is a very unreactive metal and cannot be dissolved easily by other acids alone.


22. Which of the following is not a mineral acid?

(a) Hydrochloric acid

(b) Citric acid

(c) Sulphuric acid

(d) Nitric acid

Explanation:

(b) Citric acid is not a mineral acid as it is an organic acid commonly found in citrus fruits. Mineral acids, on the other hand, are inorganic acids that are usually obtained by the reaction of an acid with a mineral substance.


23. Among the following, which is not a base?

(a) NaOH

(b) KOH

(c) NH4OH

(d) C2H5 OH

Explanation:

The correct answer is (d) C2H5OH. It is not a base but an alcohol. The other options (a) NaOH, (b) KOH, and (c) NH4OH are all bases - NaOH and KOH are strong bases, while NH4OH is a weak base.


24. Which of the following claims is untrue?

(a)All metal carbonates combine with acid to produce salt, water, and carbon dioxide.

(b) All metal oxides combine with water to produce salt and acid.

(c)Salt and hydrogen are produced react with acids 

 (d)and non-metal oxides react with water to form an acid.

Explanation:

(b) All metal oxides react with water to give salt and acid is not correct. The correct statement is: All metal oxides react with water to give metal hydroxide (base) and hydrogen ions.


25. Match the chemical substances given in Column (A) with their appropriate application given in Column (B)

Column (A)

Column (B)

(A) Bleaching powder

(i) Preparation of glass

(B) Baking soda

(ii) Production of H2 and Cl2

(C) Washing soda

(iii) Decolourisation

(D) Sodium chloride

(iv) Antacid

(a) A—(ii), B—(i), C—(iv), D—(iii)

(b) A—(iii), B—(ii), C—(iv), D—(i)

(c) A—(iii), B—(iv), C—(i), D—(ii)

(d) A—(ii), B—(iv), C—(i), D—(iii)

Explanation:

The answer is (c) A—(iii), B—(iv), C—(i), D—(ii)

26. Equivalent amounts of sodium hydroxide and hydrochloric acid solutions at the same concentration are combined, and the resulting solution's pH is assessed using a pH paper. What colour would be the result? (You can refer to the colour palette in Figure 2.2.pH paper

(a) Red

(b) Yellow

(c) Yellowish green

(d) Blue

Explanation:

When hydrochloric acid and sodium hydroxide react, they form salt and water. The resulting solution is neutral in nature. Hence, the pH of the resulting solution would be 7 and the colour obtained on the pH paper would be green (as shown in Figure 2.2).


27. Which of the following statements about HCl (g) and water are true?

I Because it is a covalent molecule, it does not ionise in the solution.

It ionises in the solution (ii).

(iii) It provides the solution with both hydrogen and hydroxyl ions.

(iv) The interaction of the hydrogen ion with the water molecule causes the formation of the hydronium ion in the solution. 

(a) (i) only

(b) (iii) only

(c) (ii) and (iv)

(d) (iii) and (iv)

Explanation:

The correct option is (d) (iii) and (iv).

When HCl (g) is passed through water, it dissolves in the water to form hydrochloric acid (HCl) which is an aqueous solution of HCl. The dissolved HCl molecule reacts with water molecule to form hydronium ion (H3O+) and chloride ion (Cl-).

The reaction can be represented as:

HCl (g) + H2O(l) → H3O+(aq) + Cl-(aq)

Therefore, option (ii) is not correct as HCl ionises in the solution, and options (i) and (ii) are not complete as they do not mention the formation of hydronium ion in the solution.


28. Which of the following assertions regarding acids is accurate?

(a)A bitter taste will turn red litmus paper blue,

(b) a sour taste will turn red paper blue, 

(c)a sour taste will turn blue litmus paper red,

Explanation:

The correct statement for acids is: (c) They are sour in taste and change blue litmus to red. This is because acids are substances that release hydrogen ions (H+) in aqueous solutions. When an acid is dissolved in water, it forms hydronium ions (H3O+). These hydronium ions react with the hydroxide ions (OH-) present in the water to form water molecules. The excess of H+ ions in the solution makes it acidic in nature. This is why acids change the colour of blue litmus paper to red. The sour taste of acids is due to the presence of H+ ions.


29. Which of the following are present in a diluted hydrochloric acid aqueous solution?

(a) H3O+ + Cl–

(b) H3O+ + OH–

(c) Cl– + OH–

(d) unionised HCl

Explanation:

The correct answer is (a) H3O+ + Cl–.


When hydrochloric acid is dissolved in water, it ionizes to form hydrogen ions (H+) and chloride ions (Cl–). In water, hydrogen ions immediately bond with water molecules to form hydronium ions (H3O+). So, the correct representation of the reaction of hydrochloric acid in water is:


HCl + H2O → H3O+ + Cl–

Therefore, the only species present in a dilute aqueous solution of hydrochloric acid are H3O+ and Cl– ions.



30. Determine the accurate illustration of the reaction that takes place during the chloralkali process

(a) 2NaCl(l) + 2H2O(l) → 2NaOH(l) + Cl2 (g) + H2 (g)

(b) 2NaCl(aq) + 2H2O(aq) → 2NaOH(aq) + Cl2 (g) + H2 (g)

(c) 2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2 (aq) + H2 (aq)

(d) 2NaCl (aq) + 2H2O (l) → 2NaOH (aq) + Cl2 (g) + H2 (g)

Explanation:

Option (b) is the correct representation of the reaction occurring during the chloralkali process. In this process, a solution of sodium chloride (NaCl) in water is electrolyzed to produce hydrogen gas (H2), chlorine gas (Cl2), and sodium hydroxide (NaOH) solution. The reaction occurs in an aqueous medium, hence NaCl and H2O are represented as aqueous (aq) solutions. The products NaOH, Cl2, and H2 are in a gaseous state as they are liberated at the electrodes during the electrolysis.


31. Match the acids given in Column (A) with their correct source given in Column (B)

Column (A)

Column (B)

(a) Lactic acid

(i) Tomato

(b) Acetic acid

(ii) Lemon

(c) Citric acid

(iii) Vinegar

(d) Oxalic acid

(iv) Curd

Explanation:

Column (A)

Column (B)

(a) Lactic acid

(iv) Curd

(b) Acetic acid

(iii) Vinegar

(c) Citric acid

(ii) Lemon

(d) Oxalic acid

(i) Tomato

Column (A) Column (B)

(a) Lactic acid (iv) Curd

(b) Acetic acid (iii) Vinegar

(c) Citric acid (ii) Lemon

(d) Oxalic acid (i) Tomato


32. Match the important chemicals given in Column (A) with the chemical formulae given in Column (B)

Column (A)

Column (B)

(a) Plaster of Paris

(i) Ca(OH)2

(b) Gypsum

(ii) CaSO4. ½ H2O

(c) Bleaching Powder

(iii)CaSO4.2H2O

(d) Slaked Lime

(iv) CaOCl2

Explanation::

Column (A)

Column (B)

(a) Plaster of Paris

(ii) CaSO4. ½ H2O

(b) Gypsum

(iii)CaSO4.2H2O

(c) Bleaching Powder

(iv) CaOCl2

(d) Slaked Lime

(i) Ca(OH)2


33. Which of the following compounds will react with litmus paper? Lemon juice, carbonated soft drink, curd, and soap solution. Moistened NH3 gas.

Explanation:

Dry HCl gas: Blue litmus paper will turn red as HCl is an acidic gas.


Moistened NH3 gas: Red litmus paper will turn blue as NH3 is a basic gas.


Lemon juice: Citric acid, which is present in lemon juice, gives it its acidic character. As a result, it will turn red the blue litmus paper.

Carbonated soft drink: Carbonated soft drinks contain carbonic acid, which makes the solution acidic. So, it will turn blue litmus paper to red.

Curd: Curd is acidic in nature due to the presence of lactic acid. So, it will turn blue litmus paper to red.


34. Provide the chemical name and name of the acid that is present in ant stings. Moreover, describe how to relieve the suffering brought on by ant stings.

Explanation:

The acid present in an ant sting is formic acid (HCOOH). The chemical formula of formic acid is HCOOH.

To get relief from the discomfort caused by ant sting, one can apply a baking soda paste or a cold compress to the affected area. Baking soda helps to neutralize the acid and reduce the pain and swelling. A cold compress can also help to reduce the swelling and provide relief from the pain. It is also advisable to avoid scratching or rubbing the affected area as it can increase the discomfort and risk of infection.


35. What happens to eggshell when nitric acid is introduced to it?

Explanation:

When nitric acid is added to eggshell, it reacts with the calcium carbonate (CaCO3) present in the eggshell and produces carbon dioxide gas (CO2), water (H2O), and calcium nitrate (Ca(NO3)2). The reaction can be represented as:


CaCO3 (s) + 2HNO3 (aq) → CO2 (g) + H2O (l) + Ca(NO3)2 (aq)

The carbon dioxide gas produced during the reaction can be observed as bubbles. The calcium nitrate formed remains in the solution. This reaction is commonly used to demonstrate the reaction of an acid with a carbonate.



36. In two different beakers, a student made solutions of I an acid and (ii) a base. She neglected to name the liquids, and the lab is devoid of litmus paper. How will she tell one solution from the other when they are both colourless?

Explanation:

The student can perform a simple test called the pH paper test to distinguish between the acid and the base solutions. The pH paper changes color depending on the pH of the solution.


To perform the test, the student can dip a strip of pH paper into each solution separately. The pH paper will change color depending on the acidity or alkalinity of the solution. If the paper turns red, then the solution is acidic, and if the paper turns blue or green, then the solution is basic.

If the color change is not distinct, the student can compare the color change of the unknown solution with that of a known acidic and basic solution. For example, if the unknown solution turns red when the pH paper is dipped in it, then it is an acid. The student can compare the color change with a known acidic solution like hydrochloric acid. If the unknown solution turns blue or green when the pH paper is dipped in it, then it is a base. The student can compare the color change with a known basic solution like sodium hydroxide.


37.  How would heating help you differentiate between baking powder and washing soda?

Explanation:

Baking powder and washing soda can be distinguished by heating as follows:


When baking powder is heated, it undergoes thermal decomposition and releases carbon dioxide gas. This is because baking powder contains a mixture of baking soda (sodium bicarbonate) and a weak acid, such as cream of tartar, which reacts with each other in the presence of heat to form carbon dioxide gas. The reaction is as follows:


NaHCO3 + H+ → Na+ + CO2 + H2O


On the other hand, when washing soda is heated, it undergoes dehydration and forms soda ash (sodium carbonate) by losing water molecules. The reaction is as follows:


Na2CO3.10H2O → Na2CO3 + 10H2O (on heating)

Therefore, by heating baking powder and washing soda separately, one can distinguish between the two by observing the formation of carbon dioxide gas in the case of baking powder and the loss of water molecules and formation of soda ash in the case of washing soda.


38. When salt A, which is frequently used in bread items, is heated, it transforms into salt B, which is used to remove water hardness, and a gas C is released. When lime water is exposed to gas C, it turns milky. Name A, B, and C.

Explanation:

Salt A commonly used in bakery products is sodium hydrogen carbonate (NaHCO3) also known as baking soda.


When sodium hydrogen carbonate (NaHCO3) is heated, it gets converted into another salt B, sodium carbonate (Na2CO3) also known as washing soda.


The gas C evolved is carbon dioxide (CO2) gas.


When carbon dioxide (CO2) gas is passed through lime water (calcium hydroxide solution), it turns lime water milky due to the formation of a white precipitate of calcium carbonate (CaCO3) according to the following reaction:


Ca(OH)2 + CO2 → CaCO3 + H2O


Therefore, the reaction can be represented as:


2 NaHCO3 (s) → Na2CO3 (s) + CO2 (g) + H2O (l)

Hence, A is NaHCO3 (sodium hydrogen carbonate or baking soda), B is Na2CO3 (sodium carbonate or washing soda) and C is CO2 (carbon dioxide) gas.



39. A gas X is produced as a by-product in one of the industrial procedures used to make sodium hydroxide. The chemical industry uses the compound Y, which is produced by the reaction of the gas X with lime water, as a bleaching agent. Provide the chemical equation for the relevant reactions while identifying X and Y.

Explanation:

The gas X formed as a by-product in the manufacture of sodium hydroxide is chlorine gas (Cl2).


The chemical equation for the reaction is:


2NaCl + 2H2O → 2NaOH + Cl2


Chlorine gas X reacts with lime water to give a compound Y, which is bleaching powder or calcium hypochlorite [Ca(OCl)2]. The reaction is:


Cl2 + Ca(OH)2 → Ca(OCl)2 + H2O


Overall, the complete reaction is:


2NaCl + 2H2O + Cl2 → 2NaOH + Ca(OCl)2

So, the gas X is chlorine gas and the compound Y is bleaching powder or calcium hypochlorite.



40. Fill in the missing data in the following table


Salted Obtained from

Name of the Salt

Formula

Base

Acid

Ammonium chloride

NH4Cl

NH4OH

–

Copper sulphate

–

–

H2 SO4

Sodium chloride

NaCl

NaOH

–

Magnesium nitrate

Mg (NO3 ) 2

–

HNO3

Potassium sulphate

K2 SO4

–

–

Calcium nitrate

Ca(NO3 ) 2

Ca(OH)2

–

Explanation:


Salted Obtained from

Name of the Salt

Formula

Base

Acid

Ammonium chloride

NH4Cl

NH4OH

HCl

Copper sulphate

CuSO4

Cu(OH)2

H2 SO4

Sodium chloride

NaCl

NaOH

HCl

Magnesium nitrate

Mg (NO3 ) 2

Mg(OH)2

HNO3

Potassium sulphate

K2 SO4

KOH

H2SO4

Calcium nitrate

Ca(NO3 ) 2

Ca(OH)2

HNO3

41. Which acids are strong and weak? Separate the strong acids from the weak acids in the following list of acids. Acids such as hydrochloric, citric, acetic, nitric, formic, and sulfuric acid.

Explanation:

Strong acids are the acids that completely ionize in water to give H+ ions. Weak acids are the acids that do not completely ionize in water and exist in the solution in the unionized form as well as the ionized form.

Among the given acids, hydrochloric acid (HCl), nitric acid (HNO3), and sulphuric acid (H2SO4) are strong acids. Citric acid (C6H8O7), acetic acid (CH3COOH), and formic acid (HCOOH) are weak acids. 



42. A gas that is used in the hydrogenation of oil is produced when zinc metal is treated with a diluted solution of a strong acid. Identify the evolved gas. Provide a test to identify the gas generated in addition to the chemical equation for the reaction.

Explanation:

When zinc metal is treated with a dilute solution of a strong acid like hydrochloric acid, hydrogen gas is evolved.


The chemical equation for the reaction is:

Zn (s) + 2HCl (aq) → ZnCl2 (aq) + H2 (g)

To detect the gas formed, we can perform the pop test. In this test, a burning matchstick is brought near the mouth of the test tube containing the gas. If the gas is hydrogen, it will burn with a pop sound.


43. What would happen if the adjustments below were made to the following schematic diagram for the production of hydrogen gas, as illustrated in Figure 2.3?preparation of hydrogen gas

(a) The test tube is filled with the same amount of zinc dust instead of zinc granules.

(b) Diluted hydrochloric acid is used in place of diluted sulfuric acid. 

(c) Copper turnings are used in place of zinc. 

(d) The tube is heated and sodium hydroxide is added in place of the diluted sulfuric acid.

Explanation:

(a) If the same amount of zinc dust is taken instead of zinc granules, the rate of the reaction will increase. This is because the surface area of zinc dust is higher than that of zinc granules, and thus more surface area will be available for the reaction to take place.

(b) If dilute hydrochloric acid is taken instead of dilute sulphuric acid, hydrogen gas will still be evolved as both hydrochloric acid and sulphuric acid are strong acids and will react with zinc to produce hydrogen gas.

(c) If copper turnings are taken instead of zinc, no reaction will take place as copper is below hydrogen in the reactivity series and cannot displace hydrogen from dilute sulphuric acid.

(d) If sodium hydroxide is taken in place of dilute sulphuric acid and the tube is heated, hydrogen gas will not be evolved as sodium hydroxide is a strong base and will not react with zinc to produce hydrogen gas. Instead, sodium zincate and water will be produced according to the following equation:

Zn + 2NaOH → Na2ZnO2 + H2O


44. Baking powder is used to make cakes. 

(a)How and why will the taste of the cake change if your mother makes a cake at home using baking soda rather than baking powder?

 (c) What is the process for turning baking soda into baking powder?

(d)What function does the tartaric acid added to baking soda serve in ?

Explanation:

(A) Baking soda is a base, and using too much of it can make a cake taste bitter. If baking soda is used in a cake instead of baking powder, the cake's flavour will be affected. The cake rises as a result of the reaction between baking soda and the acidic elements in the cake mix, which produces carbon dioxide gas. If baking soda is added in excess, it may neutralise the acidic substances and produce a bitter taste.

(b) Baking powder can be made by mixing baking soda (base), cream of tartar (acidic salt), and cornstarch (stabilizer). The cream of tartar provides the acidic component, and the cornstarch helps to keep the mixture stable and prevents the baking soda from reacting with the acidic component prematurely.

(c) Tartaric acid is added to baking soda to react with it and produce carbon dioxide gas. Tartaric acid acts as the acidic component in the baking powder and reacts with the baking soda (base) to produce carbon dioxide gas. The carbon dioxide gas produced helps in the leavening of the cake, making it light and fluffy



45. When a metal carbonate X reacts with acid, a gas is produced, which, after passing through a solution Y, releases the carbonate once more. On the other hand, when dry Y is passed over a gas G produced at the anode during the electrolysis of brine, a chemical Z is produced that is utilised to sanitise drinking water. You are X, Y, G, and Z.

Explanation:

The given information suggests that the metal carbonate X can be decomposed by the acid to give a gas, which is carbon dioxide (CO2) and the salt of the acid and the metal cation. When this CO2 gas is passed through the solution Y, the original carbonate X is regenerated.


So, the reaction at first can be represented as:

XCO3(s) + 2HCl(aq) → XCl2(aq) + CO2(g) + H2O(l)


And, when CO2 is passed through the solution Y, it will react as follows:

CO2(g) + H2O(l) ⇌ H2CO3(aq)

H2CO3(aq) + XCl2(aq) → XCO3(s) + 2HCl(aq)


Thus, the solution Y must be containing an alkali or a base which reacts with CO2 to form an acid (carbonic acid, H2CO3) that can further react with XCl2 to form XCO3.


The gas G obtained at the anode during electrolysis of brine is chlorine gas (Cl2). When Cl2 is passed through dry Y, it reacts to form a strong oxidizing agent called sodium hypochlorite (NaClO) which is used for disinfecting drinking water.


The reaction can be represented as:

2NaOH(aq) + Cl2(g) → NaClO(aq) + NaCl(aq) + H2O(l)


Therefore, based on the given information, we can conclude the following:


X is a metal carbonate that can be decomposed by acid to form CO2 and can be regenerated by passing CO2 through a solution containing an alkali or a base.

Y is a solution containing an alkali or a base that can react with CO2 to form carbonic acid.

G is chlorine gas obtained during the electrolysis of brine.

Z is sodium hypochlorite, which is formed by reacting chlorine gas with a solution of sodium hydroxide.


46. When left out in the open, a dry pellet of a common base B will start to absorb moisture and become sticky. The substance is a leftover from the chloralkali process. Determine B. What kind of reaction takes place when an acidic oxide is applied to B? For one of these solutions, create a balanced chemical equation.

Explanation:

The common base B described in the question is sodium hydroxide (NaOH).


When sodium hydroxide (base) reacts with an acidic oxide, it undergoes a neutralization reaction and forms a salt and water.


For example, when sodium hydroxide reacts with sulfuric acid (H2SO4), sodium sulfate (Na2SO4) and water (H2O) are formed.

NaOH + H2SO4 → Na2SO4 + 2H2O

This reaction is a neutralization reaction where the acidic oxide, sulfuric acid, neutralizes the basic oxide, sodium hydroxide. The products formed are a salt and water.



47. A white, malleable substance, sulphate salts are found in Group 2 of the Periodic Table and can be formed into a variety of shapes using dough. This substance solidifies into a mass when exposed to air for a while, making it impossible to mould. What kind of sulphate salt is this, and why is it acting this way? Provide the resulting response.

Explanation:

The sulphate salt of Group 2 element of the Periodic Table is Calcium Sulphate (CaSO4).


Calcium Sulphate shows such behaviour because it has a property of absorbing water and becomes hydrated. When Calcium Sulphate is exposed to moisture, it reacts with it and forms Calcium Sulphate Hemihydrate (CaSO4.1/2H2O) which is a solid mass and cannot be used for moulding purposes.


The reaction involved is:

CaSO4 + 1/2H2O → CaSO4.1/2H2O


48. On the basis of the reactions listed below, name the chemical X. Include A, B, and C's names and chemical formulas as well.

compound X


Explanation


1)2NaOH+ Zn→ Na₂ZnO₂ + H2(g)

2)NaOH + HCl →NaCl + H2O

3)NaOH + CH3 COOH→ CH3 COONa + H2O

By the following reaction, it is confirmed that compound X is Sodium hydroxide.

Reaction 2 (NaOH + HCl → NaCl + H2O) is a typical neutralization reaction of a strong base (NaOH) with a strong acid (HCl) to produce a salt (NaCl) and water. This reaction confirms the presence of NaOH in the compound X.