Acids, Bases And Salts - Class 10 MCQ

What happens when a solution of an acid is mixed with a solution of a base in a test tube?

When a solution of an acid is mixed with a solution of a base in a test tube, several changes occur. The resulting mixture undergoes a chemical reaction known as neutralization, where the acid and base react to form a salt and water. This reaction can have several effects, including changes in temperature and the formation of a salt.

Temperature Change:

• Temperature of the solution increases: In some cases, the neutralization reaction between an acid and a base is exothermic, meaning it releases heat. This can cause the temperature of the solution to increase.


• Temperature of the solution decreases: On the other hand, some neutralization reactions can be endothermic, absorbing heat from the surroundings and causing the temperature of the solution to decrease. However, this is less common.


• Temperature of the solution remains the same: In some cases, the neutralization reaction is neither exothermic nor endothermic, resulting in no significant change in temperature.

Salt Formation:

• Salt formation takes place: When an acid reacts with a base, the hydrogen ions from the acid combine with the hydroxide ions from the base to form water. The remaining ions from the acid and base combine to form a salt. This salt can often be observed as a solid precipitate or remain dissolved in the resulting solution.

Overall, the reaction between an acid and a base in a test tube can result in a change in temperature and the formation of a salt.

To understand the role of calcium chloride in the guard tube when preparing hydrogen chloride gas on a humid day, let's break down the process and the properties of calcium chloride:
1. Preparation of Hydrogen Chloride Gas:
- Hydrogen chloride gas is usually prepared by reacting a metal chloride with a strong acid, such as sulfuric acid.
- The reaction can be represented as: Metal chloride + Sulfuric acid → Hydrogen chloride gas + Metal sulfate
2. Humidity and Moisture:
- On a humid day, the air contains a significant amount of moisture or water vapor.
- Moisture can interfere with the preparation of hydrogen chloride gas by affecting the purity and concentration of the gas.
3. The Role of Calcium Chloride:
- Calcium chloride is a highly hygroscopic compound, meaning it has a strong affinity for water and readily absorbs moisture from the surrounding environment.
- When hydrogen chloride gas is passed through the guard tube containing calcium chloride, the calcium chloride serves the following purposes:
- Absorbing Moisture from the Gas: The calcium chloride in the guard tube absorbs moisture from the hydrogen chloride gas, preventing it from interfering with the purity of the gas.
- Drying the Gas: By removing moisture from the gas, calcium chloride helps to ensure that the hydrogen chloride gas obtained is dry and free from water vapor.
- Protecting the Apparatus: Absorbing moisture with calcium chloride prevents the formation of corrosive acids that can damage the apparatus used in the preparation of hydrogen chloride gas.
Therefore, the correct answer is C: absorb moisture from the gas.

Tomato is a natural source of which acid?
Tomatoes are a widely consumed vegetable that is not only delicious but also packed with various nutrients. One of the acids found in tomatoes is oxalic acid.
Oxalic Acid:
- Oxalic acid is a naturally occurring organic compound found in many fruits and vegetables, including tomatoes.
- It is a dicarboxylic acid with the chemical formula C2H2O4.
- Oxalic acid is known for its sour taste and is also found in other foods like spinach, rhubarb, and beet greens.
- In tomatoes, oxalic acid is present in small amounts and contributes to the tangy taste of the fruit.
- It is important to note that oxalic acid can form crystals in the body, which may lead to kidney stones in individuals who are susceptible to them.
While tomatoes do contain oxalic acid, it is not the only acid present in the fruit. Tomatoes also contain other organic acids such as citric acid and malic acid, but in smaller quantities compared to oxalic acid.
In conclusion, tomatoes are a natural source of oxalic acid, along with other organic acids such as citric acid and malic acid.

Explanation:

Brine is an aqueous solution of sodium chloride. Here's a detailed explanation:

Aqueous
- An aqueous solution refers to a solution in which the solvent is water.
- In the case of brine, the solvent is water, making it an aqueous solution.


Sodium Chloride:
- Sodium chloride is a compound composed of sodium cations (Na+) and chloride anions (Cl-).
- It is commonly known as table salt and has the chemical formula NaCl.
- Brine is made by dissolving sodium chloride in water, resulting in an aqueous solution of sodium chloride.


Other Options:
- Sodium hydroxide (NaOH) is a strong base, and an aqueous solution of sodium hydroxide is called sodium hydroxide solution, not brine.
- Sodium carbonate (Na2CO3) is a salt that can form an aqueous solution, but it is not commonly referred to as brine.
- Sodium bicarbonate (NaHCO3) is a salt that can also form an aqueous solution, but it is not commonly referred to as brine.


Therefore, the correct answer is C: aqueous solution of sodium chloride.

To determine the correct answer, we need to understand the properties and uses of each compound.
Na₂CO₃ · 10H₂O:
- Na₂CO₃ · 10H₂O is a chemical formula for sodium carbonate decahydrate.
- It is commonly known as "washing soda" or "soda ash."
- The compound is a white crystalline substance that contains water molecules in its structure.
- It is highly soluble in water and has a strong alkaline nature.
- Washing soda is mainly used in laundry detergents, water treatment, and as a cleaning agent.
Baking Soda:
- Baking soda, also known as sodium bicarbonate (NaHCO₃), is a different compound from Na₂CO₃ · 10H₂O.
- Baking soda is a white crystalline powder that is also soluble in water.
- It is commonly used in baking as a leavening agent to help dough rise.
- Baking soda also has various other household uses, such as cleaning, deodorizing, and as an antacid.
Bleaching Powder:
- Bleaching powder, or calcium hypochlorite (Ca(ClO)₂), is a completely different compound from Na₂CO₃ · 10H₂O.
- It is a white powder with a strong chlorine odor.
- Bleaching powder is commonly used as a disinfectant, for bleaching purposes, and as a water treatment agent.
Tartaric Acid:
- Tartaric acid, or C₄H₆O₆, is yet another different compound from Na₂CO₃ · 10H₂O.
- It is a crystalline organic acid that is commonly found in fruits like grapes.
- Tartaric acid is used in the food and beverage industry as an acidulant, flavor enhancer, and stabilizer.
Based on the above information, we can conclude that the correct answer is A: washing soda, as Na₂CO₃ · 10H₂O is the chemical formula for washing soda.

Formation of Plaster of Paris
Plaster of Paris is a form of gypsum that is created by heating gypsum to a specific temperature. The process involves the following steps:
1. Heating temperature: Gypsum is heated to a specific temperature to form Plaster of Paris.
2. Temperature required: The temperature required to form Plaster of Paris is 100°C.
3. Heating process: Gypsum is heated in a kiln or oven until it reaches the desired temperature.
4. Chemical reaction: During the heating process, gypsum undergoes a chemical reaction known as calcination. This reaction involves the loss of water molecules from the gypsum, resulting in the formation of Plaster of Paris.
5. Water loss: The heating process causes the gypsum to lose approximately 75% of its water content, leaving behind a dry powder known as Plaster of Paris.
6. Setting process: Plaster of Paris can be mixed with water to form a paste that can be molded into various shapes. When the paste is allowed to dry, it hardens and forms a solid structure.
Therefore, the correct answer is B: 100°C. At this temperature, gypsum is heated to form Plaster of Paris through the process of calcination.

Explanation:

Sodium carbonate (Na2CO3) is a basic salt because it is the salt of a weak acid and a strong base. Here's why:

Definition of a basic salt:

A basic salt is a salt that is formed from the neutralization of a weak acid with a strong base. It has a pH greater than 7 and can act as a base when dissolved in water.

Components of sodium carbonate:

Sodium carbonate consists of the sodium ion (Na+) and the carbonate ion (CO3^2-).

Acidic and basic properties of the ions:

The sodium ion (Na+) is derived from a strong base (sodium hydroxide, NaOH) and is therefore neutral and does not contribute to the basic nature of the salt.

The carbonate ion (CO3^2-) is derived from a weak acid (carbonic acid, H2CO3) and a strong base (sodium hydroxide, NaOH). The carbonate ion can accept protons (H+) from water, making it a weak base.

Neutralization reaction:

When sodium carbonate reacts with water, it undergoes hydrolysis:

Na2CO3 + H2O → 2NaOH + H2CO3

The hydrolysis of the carbonate ion produces hydroxide ions (OH-) which make the solution basic.

Conclusion:

Sodium carbonate is a basic salt because it is the salt of a weak acid (carbonic acid) and a strong base (sodium hydroxide).

(i) Higher the pH, stronger the acid:

• A higher pH indicates a more basic solution, not a stronger acid. The pH scale measures the acidity or alkalinity of a solution, with a pH of 7 being neutral, pH values below 7 indicating acidity, and pH values above 7 indicating alkalinity.


• Therefore, this statement is incorrect.

(ii) Higher the pH, weaker the acid:

• This statement is correct. As the pH of a solution increases, the concentration of hydrogen ions (H+) decreases, and therefore the acidity decreases. A higher pH indicates a weaker acid.

(iii) Lower the pH, stronger the base:

• This statement is incorrect. As mentioned earlier, a lower pH indicates a more acidic solution, not a stronger base. A stronger base would have a higher pH.

(iv) Lower the pH, weaker the base:

• This statement is correct. A lower pH indicates a higher concentration of hydrogen ions (H+), which makes the solution more acidic and therefore weaker as a base.

Therefore, the correct statement is (ii) and (iv), which means the answer is D.

Nettle Sting and its Natural Source of Acid

• Nettle sting refers to the sensation and skin reaction that occurs when a person comes into contact with the fine hairs on the leaves and stems of stinging nettle plants.


• Nettle stings are caused by the chemicals present in the hairs, including histamine, acetylcholine, and formic acid.


• Formic acid is the natural source of acid found in the nettle sting.


• Formic acid is a colorless liquid with a strong, pungent odor. It is commonly found in the venom of stinging insects such as ants and bees.


• When a person is stung by a nettle, the formic acid is released into the skin, causing a burning and irritating sensation.


• Formic acid is also responsible for the characteristic redness, swelling, and itchiness that occur after a nettle sting.

Conclusion

In conclusion, the natural source of acid found in nettle sting is formic acid. This acid is responsible for the burning sensation and skin reaction that occurs when a person comes into contact with stinging nettle plants.