All questions of Acids, Base and Salts for Class 7 Exam

Some of the natural indicators are red cabbage juice, onion paste, turmeric, lemon juice etc. Natural indicators are turmric,litmus,china rose etc are some natural indicators. Some Natural Indicators are red Cabbage juice,turmeric,china rose[hibiscus] and litmus.

Lemon juice is acidic, so when tested with China rose indicator, it will turn dark pink (magenta). This color change indicates the acidic nature of the solution, as China rose turns acidic solutions to dark pink.

Excessively acidic soil is treated with bases like quick lime (calcium oxide) or slaked lime (calcium hydroxide). These substances neutralize the acidity of the soil, improving its suitability for plant growth.

Actually tomato contains oxalic acid.
tamarind contains tartaric acid
phosphoric is used for fertilizers, detergents and soft drinks
lactic acid is produced when you do exercises i.e the muscle cells and red blood cells produces lactic acid
so we can conclude that oxalic acid is present in tomato

Explanation:
•Putting a drop of soap solution on turmeric paper will make the paper turn into red color.
•That is because due to the process of indication.
•Turmeric turns red when reacted with base and green when reacted with acid.
•Soap solution is a base
Conclusion:
Turmeric paper when reacted with soap solution(base) turns the color of the paper red.

Understanding Acid Rain
Acid rain is a significant environmental issue resulting from human activities and natural processes. It occurs when certain pollutants mix with rainwater, leading to harmful effects on ecosystems, buildings, and human health.
Key Pollutants
The primary substances responsible for acid rain are:

• Sulphur Dioxide (SO2): This gas is released from burning fossil fuels, such as coal and oil, and from industrial processes. When it enters the atmosphere, it can combine with oxygen and water vapor to form sulfuric acid.
• Nitrogen Dioxide (NO2): This pollutant comes from vehicle emissions and power plants. It reacts with water vapor in the air to produce nitric acid.

Formation of Acid Rain
When sulphur dioxide and nitrogen dioxide mix with raindrops in the atmosphere, the following reactions occur:

• Formation of Sulfuric Acid: SO2 reacts with oxygen and water to form H2SO4 (sulfuric acid).
• Formation of Nitric Acid: NO2 reacts with water to form HNO3 (nitric acid).

These acids dissolve in the rainwater, resulting in acid rain, which has a lower pH than normal rainwater.
Effects of Acid Rain
Acid rain can lead to various detrimental effects, including:

• Damage to forests and vegetation.
• Acidification of lakes and rivers, harming aquatic life.
• Corrosion of buildings and monuments, especially those made of limestone and marble.
• Negative impacts on soil chemistry, affecting agriculture.

In summary, option 'B' is correct as sulphur dioxide and nitrogen dioxide are the key substances that contribute to the formation of acid rain, making it a pressing environmental concern.

Introduction:
Acidic soil is characterized by a low pH level, typically below 7. This type of soil can be problematic for plant growth as it affects nutrient availability and can lead to nutrient deficiencies. To improve the pH level of acidic soil, a base is commonly used to neutralize the acidity and make it more suitable for plant growth.

Base commonly used to treat acidic soil:
The correct base commonly used to treat acidic soil is Calcium Hydroxide (option D).

Explanation:
Calcium hydroxide, also known as agricultural lime or garden lime, is a common base used to treat acidic soil. It is an alkaline substance and has the ability to neutralize the acidity in the soil by increasing the pH level.

How does Calcium Hydroxide work?
When calcium hydroxide is applied to acidic soil, it reacts with the hydrogen ions (H+) present in the soil solution. This reaction results in the formation of water and calcium ions (Ca2+). The calcium ions then combine with carbonate ions (CO32-) naturally present in the soil to form calcium carbonate (CaCO3). Calcium carbonate is a neutral compound that helps to raise the soil pH and reduce its acidity.

Benefits of using Calcium Hydroxide:
Using calcium hydroxide to treat acidic soil offers several benefits:

1. Neutralizes soil acidity: The primary benefit of using calcium hydroxide is its ability to neutralize soil acidity by raising the pH level. This creates a more favorable environment for plant growth.

2. Increases nutrient availability: Acidic soil tends to lock up essential nutrients, making them less available to plants. By raising the pH level, calcium hydroxide helps to release these nutrients, making them more accessible for plant uptake.

3. Improves soil structure: Acidic soil is often compacted and poorly structured. The application of calcium hydroxide can help improve soil structure by promoting better aggregation and allowing for better water infiltration and root penetration.

4. Enhances microbial activity: Many beneficial soil microorganisms prefer a neutral pH environment. By neutralizing soil acidity, calcium hydroxide can promote the growth and activity of these beneficial microorganisms, improving overall soil health.

Conclusion:
In conclusion, calcium hydroxide (option D) is commonly used as a base to treat acidic soil. Its ability to neutralize acidity, increase nutrient availability, improve soil structure, and enhance microbial activity makes it an effective choice for improving the pH level of acidic soil and creating a more suitable environment for plant growth.

Organic matter, such as compost, releases acids when decomposed. These acids help to neutralize the basic nature of the soil, making it more suitable for plant growth.

In a neutralization reaction, an acid reacts with a base to form salt and water. This process is characterized by the combination of H⁺ ions from the acid and OH⁻ ions from the base to form water (H₂O), and the remaining ions form a salt.

Phenolphthalein is a commonly used synthetic indicator to test the acidic or basic nature of a substance. Here is an explanation of why phenolphthalein is used as an indicator and how it works:

Indicators:
Indicators are substances that change their color in the presence of acids or bases. They are used to detect the presence and determine the nature of these substances in a solution. Indicators exist in both natural and synthetic forms. Synthetic indicators are often preferred due to their stability and reliability.

Phenolphthalein:
Phenolphthalein is a synthetic indicator that is frequently used in acid-base titrations and to test the pH of a substance. It is a colorless compound in its acidic form and turns pink or purple in the presence of a base. Phenolphthalein can be used to detect both strong and weak bases.

Working of Phenolphthalein:
When phenolphthalein is added to a solution, it undergoes a chemical reaction with the base present in the solution. In an acidic solution, the concentration of H+ ions is high, and these ions react with phenolphthalein to keep it colorless. However, in a basic solution, the concentration of OH- ions is high, and they react with phenolphthalein to produce an ion that is pink or purple in color.

Color Change:
The color change of phenolphthalein from colorless to pink or purple occurs at a specific pH range, known as the indicator's transition range. For phenolphthalein, the transition range is typically between pH 8.2 and 10.0. This means that phenolphthalein will remain colorless in acidic solutions with a pH below 8.2, but as the pH increases and becomes more basic, the indicator will gradually turn pink or purple.

Conclusion:
Phenolphthalein is a commonly used synthetic indicator to test the acidic or basic nature of a substance. Its colorless to pink/purple color change in the presence of a base makes it a reliable indicator for determining the pH of a solution.

Importance of Neutralizing Factory Wastes Before Disposal into Water Bodies

Preventing the Killing of Aquatic Organisms
- When factory wastes contain acids or other harmful chemicals, they can have devastating effects on aquatic life.
- The acidic nature of the waste can disrupt the pH balance of the water, making it unsuitable for many aquatic organisms.
- Aquatic organisms may suffer from burns, organ damage, or even death when exposed to acidic waste.

Protecting the Ecosystem
- Aquatic organisms play a crucial role in the ecosystem by maintaining the balance of the food chain.
- If these organisms are killed off due to the acidic factory waste, it can lead to a ripple effect throughout the ecosystem.
- Other species that depend on these organisms for food or habitat may also be affected, causing a domino effect of negative consequences.

Promoting Water Quality
- Neutralizing factory wastes before disposal helps to maintain the quality of water bodies.
- Clean water is essential for human consumption, agriculture, and the overall health of the environment.
- By preventing the introduction of harmful chemicals into water bodies, we can ensure that the water remains safe and usable for various purposes.
In conclusion, neutralizing factory wastes before disposal into water bodies is crucial to prevent the killing of aquatic organisms and protect the ecosystem. It also helps to promote water quality and ensure the sustainability of our natural resources.

Acid present in soured curd is Lactic acid

Explanation:
- Lactic acid is the acid present in soured curd: When milk is left to ferment, it undergoes a process where bacteria convert the lactose (milk sugar) into lactic acid. This gives the curd its characteristic tangy flavor.
- Role of Lactic Acid: Lactic acid is responsible for the sour taste and also helps in preserving the curd by creating an acidic environment that inhibits the growth of harmful bacteria.
- Health Benefits: Lactic acid produced during the fermentation of curd is also beneficial for gut health as it promotes the growth of beneficial bacteria in the gut.
- Other Acids: While lactic acid is the main acid present in soured curd, other acids such as acetic acid (found in vinegar), tartaric acid (found in grapes), and oxalic acid (found in spinach and rhubarb) may be present in other food items but not in curd.
Therefore, the acid present in soured curd is lactic acid, making it a popular and nutritious dairy product enjoyed by many.

Calcium Carbonate is not a base because:
- Definition of a base:
Bases are substances that can accept protons (H⁺ ions) or donate hydroxide ions (OH⁻ ions) in a chemical reaction. They have a pH greater than 7.
- Calcium Carbonate:
Calcium carbonate (CaCO₃) is a chemical compound that is commonly found in rocks and shells. It is not a base because it does not ionize in water to produce hydroxide ions (OH⁻). When calcium carbonate reacts with acids, it forms salts and releases carbon dioxide gas, but it does not produce hydroxide ions like typical bases.
- Examples of bases:
1. Magnesium hydroxide (Mg(OH)₂)
2. Calcium hydroxide (Ca(OH)₂)
3. Sodium hydroxide (NaOH)
- Acid-Base reactions:
Bases like magnesium hydroxide, calcium hydroxide, and sodium hydroxide can neutralize acids by accepting protons to form water and a salt. This is a characteristic reaction of bases.
In conclusion, calcium carbonate is not considered a base because it does not fit the definition of a base based on its chemical properties and behavior in reactions with acids.

Role of Bases in Treating Factory Wastes

Neutralization of Acid
Bases play a crucial role in treating factory wastes by neutralizing the acid present in the waste. Many industrial processes produce acidic waste products, which can be harmful to the environment if not properly treated. When bases are added to acidic wastes, a neutralization reaction occurs, resulting in the formation of water and a salt. This process helps to reduce the acidity of the waste, making it less harmful to the environment.

Prevention of Environmental Damage
By neutralizing the acid in factory wastes, bases help to prevent environmental damage. Acidic wastes can contaminate soil, water, and air, leading to harmful effects on plants, animals, and humans. Neutralizing the acid in these wastes helps to reduce their harmful impact on the environment, protecting ecosystems and human health.

Facilitation of Waste Treatment
Bases also play a role in facilitating the treatment of factory wastes. By neutralizing the acid, bases help to stabilize the waste, making it easier to handle and dispose of properly. This process enables the effective treatment and management of industrial wastes, ensuring that they do not pose a threat to the environment or public health.
In conclusion, bases play a critical role in treating factory wastes by neutralizing the acid present in the waste. This process helps to prevent environmental damage, facilitate waste treatment, and protect ecosystems and human health from the harmful effects of acidic industrial wastes.

Using turmeric indicator, a sugar solution will not change color, hydrochloric acid will remain unchanged, and sodium hydroxide will turn the turmeric indicator red due to its basic nature.

Distilled water is neutral, with a pH of around 7. It does not change the color of either blue or red litmus paper, which signifies its neutral nature.

Chemical Name of Common Salt Formed during Neutralization of Sodium Hydroxide and Hydrochloric Acid:

When sodium hydroxide (NaOH) and hydrochloric acid (HCl) react together in a neutralization reaction, a chemical compound called sodium chloride (NaCl) is formed. Sodium chloride is commonly known as table salt.

Neutralization Reaction:
The reaction between sodium hydroxide and hydrochloric acid can be represented by the following balanced chemical equation:

NaOH + HCl → NaCl + H2O

In this reaction, one molecule of sodium hydroxide reacts with one molecule of hydrochloric acid to produce one molecule of sodium chloride and one molecule of water.

Explanation:

- Sodium hydroxide (NaOH) is a strong base, and hydrochloric acid (HCl) is a strong acid. When these two substances react together, they undergo a neutralization reaction.
- In a neutralization reaction, an acid reacts with a base to form a salt and water. The acidity of the acid is neutralized by the basicity of the base, resulting in the formation of a neutral product.
- In the case of the reaction between sodium hydroxide and hydrochloric acid, the sodium ion (Na+) from sodium hydroxide combines with the chloride ion (Cl-) from hydrochloric acid to form sodium chloride (NaCl).
- The other product of the reaction is water (H2O), which is formed by the combination of the hydrogen ion (H+) from hydrochloric acid and the hydroxide ion (OH-) from sodium hydroxide.
- Sodium chloride is a white crystalline solid that is highly soluble in water. It is widely used as a seasoning and preservative in food, as well as in various industrial processes.
- The chemical formula for sodium chloride is NaCl, where Na represents sodium and Cl represents chlorine.

Conclusion:

The chemical name of the common salt formed during the neutralization of sodium hydroxide and hydrochloric acid is sodium chloride (NaCl). This reaction is a typical example of a neutralization reaction, where a salt and water are produced by the combination of an acid and a base. Sodium chloride, or table salt, is widely used in various applications due to its numerous properties and uses.

Antacids like milk of magnesia contain basic substances that neutralize the excessive acid in the stomach, providing relief from the discomfort and pain associated with indigestion.

Milk of Magnesia provides relief from indigestion by acting as a base.

Indigestion, also known as dyspepsia, is a common condition characterized by discomfort or pain in the upper abdomen. It is often caused by excessive stomach acid or an imbalance in the digestive system. Milk of Magnesia, a popular over-the-counter medication, is commonly used to relieve indigestion symptoms. It contains magnesium hydroxide, which acts as an antacid and helps neutralize excess stomach acid.

How Milk of Magnesia works:

1. Alkaline properties: Milk of Magnesia is an alkaline substance, meaning it has a high pH level. When consumed, it reacts with the stomach acid, which has a low pH level, and helps neutralize it. This neutralization process reduces the overall acidity in the stomach, providing relief from indigestion symptoms.

2. Buffering effect: The active ingredient in Milk of Magnesia, magnesium hydroxide, acts as a buffering agent. It absorbs excess acid and converts it into magnesium chloride and water. This process helps maintain the pH balance in the stomach and prevents acid-related discomfort.

3. Coating effect: Milk of Magnesia also has a soothing effect on the lining of the stomach and esophagus. It forms a protective coating that helps alleviate irritation and inflammation caused by stomach acid. This coating effect can provide relief from symptoms like heartburn and sour stomach.

4. Regulation of bowel movements: In addition to its antacid properties, Milk of Magnesia is also known for its mild laxative effect. It helps relieve constipation by drawing water into the colon, softening the stool, and promoting bowel movements. This can be beneficial for individuals experiencing indigestion symptoms related to constipation.

5. Overall relief: By acting as a base, neutralizing stomach acid, and providing a protective coating, Milk of Magnesia helps alleviate the discomfort associated with indigestion. It provides relief from symptoms such as heartburn, bloating, nausea, and abdominal pain.

In conclusion, Milk of Magnesia acts as a base and helps neutralize excess stomach acid. It also provides a protective coating and regulates bowel movements, providing relief from indigestion symptoms. However, it is always advisable to consult a healthcare professional before using any medication for indigestion or other digestive issues.

The result of the neutralization reaction between hydrochloric acid and sodium hydroxide is water. This reaction is a typical example of an acid-base reaction, where an acid and a base react to form a salt and water.

Neutralization Reaction:
In a neutralization reaction, the hydrogen ions (H+) from the acid combine with the hydroxide ions (OH-) from the base to form water (H2O). The remaining ions from the acid and base combine to form a salt. In this case, the salt formed is sodium chloride (NaCl).

Chemical Equation:
The chemical equation for the neutralization reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH) is:

HCl + NaOH → NaCl + H2O

The hydrochloric acid donates a hydrogen ion (H+) to the sodium hydroxide, resulting in the formation of water and sodium chloride.

Explanation:
During the reaction, the hydrochloric acid dissociates into hydrogen ions (H+) and chloride ions (Cl-). Similarly, sodium hydroxide dissociates into sodium ions (Na+) and hydroxide ions (OH-).

The hydrogen ions from the hydrochloric acid combine with the hydroxide ions from the sodium hydroxide to form water molecules. This is an exothermic reaction, releasing energy in the form of heat.

The remaining ions, sodium (Na+) and chloride (Cl-), combine to form sodium chloride (NaCl), which is a salt. The salt remains dissolved in the water, forming a homogeneous solution.

Conclusion:
In conclusion, the neutralization reaction between hydrochloric acid and sodium hydroxide results in the formation of water and sodium chloride. This reaction is commonly used in various applications, such as in the laboratory to prepare solutions of specific pH or in everyday life for acid-base neutralization.