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.

Understanding China Rose Indicator
The statement is indeed **True**. Let's explore why.

What is China Rose Indicator?
- The China rose indicator, also known as hibiscus extract, is a natural pH indicator derived from the petals of the hibiscus flower.
- It contains anthocyanins, which change color based on the acidity or basicity of the solution.

Color Changes in Solutions
- **Acidic Solutions:**
- When added to acidic solutions (like lemon juice or vinegar), the China rose indicator turns **dark pink (magenta)**.
- This color change occurs because the anthocyanins react with hydrogen ions (H⁺) present in acidic environments.
- **Basic Solutions:**
- In contrast, when the indicator is introduced to alkaline or basic solutions (such as baking soda solution), it shifts to a **green** hue.
- This color change indicates a decrease in the concentration of hydrogen ions, resulting in a more neutral or basic environment.

Practical Applications
- The China rose indicator can be used in classrooms and laboratories to visually demonstrate the pH levels of various solutions.
- It serves as an accessible and visually engaging tool to educate students about acids, bases, and the concept of pH.

Conclusion
In summary, the China rose indicator effectively demonstrates acid-base chemistry through its color changes, confirming that the statement is **True**.

When we add phenolphthalein indicator to a base, and a base only, it turns dark pink. It does not change color in an acid or a neutral substance. If no change is observed, it is either an acid or a neutral substance. So, option c.

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

B.) sodium chloride

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.

Litmus Paper in Acidic Solution
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The color change of litmus paper when added to an acidic solution is a key indicator of the solution's pH level. Litmus paper is a pH indicator that changes color in response to the acidity or alkalinity of a solution.

Color Change to Red
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When litmus paper is added to an acidic solution, it turns red. This is because acidic solutions have a pH below 7, indicating a higher concentration of hydrogen ions. The red color change of litmus paper in an acidic solution is a result of the chemical reaction between the hydrogen ions in the acid and the dye on the litmus paper.

Explanation
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Litmus paper contains a dye that changes color in response to the concentration of hydrogen ions in a solution. In an acidic solution, there is an excess of hydrogen ions, which react with the dye on the litmus paper, causing it to turn red. This color change indicates the acidic nature of the solution.

Conclusion
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In conclusion, when litmus paper is added to an acidic solution, it turns red due to the presence of hydrogen ions. This color change is a useful indicator of the acidity of the solution and can help determine its pH level.

Neutralization Reaction:
Neutralization reaction is a chemical reaction between an acid and a base, which results in the formation of salt and water. This reaction is important in various chemical processes and is commonly used in everyday life.

Explanation:
- When an acid reacts with a base, they neutralize each other's properties.
- The hydrogen ions (H+) from the acid combine with the hydroxide ions (OH-) from the base to form water (H2O).
- The remaining ions combine to form a salt, which is a compound composed of a positive ion from the base and a negative ion from the acid.
- For example, when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), the products formed are water (H2O) and salt (NaCl).
- The reaction can be represented by the following equation: HCl + NaOH → NaCl + H2O.

Importance:
- Neutralization reactions are important in various industries such as pharmaceuticals, agriculture, and food processing.
- They are also used in environmental protection to neutralize acidic or basic wastewater before disposal.
- In everyday life, antacids are a common example of neutralization reactions used to treat indigestion and heartburn.
In conclusion, neutralization reactions involve the combination of an acid and a base to form salt and water. This process is essential in various applications and plays a crucial role in maintaining a balance in chemical systems.

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.

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.

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.

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.

Identifying substances using turmeric indicator:
Identifying substances using turmeric indicator involves observing the color changes that occur when turmeric is exposed to different solutions. Turmeric indicator is commonly used in chemistry to detect the presence of acids and bases based on color changes.

Explanation of option 'B':

Sugar solution: Sugar solution does not change the color of turmeric indicator. Therefore, when turmeric indicator is added to a sugar solution, it will not show any significant color change.

Hydrochloric acid: Hydrochloric acid turns turmeric indicator yellow. This is because hydrochloric acid is an acid and acids turn turmeric indicator yellow.

Sodium hydroxide: Sodium hydroxide turns turmeric indicator red. This is because sodium hydroxide is a base and bases turn turmeric indicator red.
Therefore, based on the color changes observed with turmeric indicator, we can conclude that option 'B' is the correct identification of the substances.

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.

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.