Important Questions Test: Acids Bases & Salts - Class 7 MCQ

• China rose indicator is like a magic potion that helps us know if a liquid is sour or sweet. When China rose meets something sour, like lemon juice, it turns the color to dark pink. But if it meets something sweet, like soda water, it changes to green.

• So, when China rose indicator meets acidic solutions, it turns them dark pink (magenta). When it meets basic solutions, it changes them to green. That's why the statement is True!

Topic in NCERT: China Rose as Indicator

Line in NCERT: "China rose indicator turns acidic solutions to dark pink (magenta) and basic solutions to green."

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.

Topic in NCERT: Soil treatment

Line in NCERT: "When the soil is too acidic, it is treated with bases like quick lime (calcium oxide) or slaked lime (calcium hydroxide)."

Factory wastes often contain acids, which can harm aquatic organisms by disrupting the water’s pH balance. Neutralizing these wastes before disposal helps protect the aquatic ecosystem by preventing the acid from causing harm.

Topic in NCERT: Factory wastes

Line in NCERT: "The wastes of many factories contain acids. If they are allowed to flow into the water bodies, the acids will kill fish and other organisms."

Since phenolphthalein turns pink in a basic solution and remains colourless in acidic and neutral solutions, if there's no change observed upon its addition, the solution must be either acidic or neutral.

Topic in NCERT: ACIDS, BASES AND SALTS

Line in NCERT: "It is evident that when the solution is basic, phenolphthalein gives a pink colour. On the other hand, when the solution is acidic, it remains colourless."

The correct answer is C: Hydrochloric acid.

Explanation:

• Bases are substances that can accept hydrogen ions (protons) or more commonly produce hydroxide ions (OH⁻) in solution.


• Magnesium hydroxide, calcium hydroxide, and sodium hydroxide are all bases because they produce hydroxide ions when dissolved in water.


• Hydrochloric acid (HCl) is an acid, not a base. It donates hydrogen ions (H⁺) in solution, which is characteristic of acids.

.

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.

Acid rain is created when substances like sulphur dioxide, and nitrogen dioxide mix with raindrops in the air. These substances make the rain harmful and can damage buildings, plants, and animals.

Topic in NCERT: Acid Rain

Line in NCERT: "the rain becomes acidic because carbon dioxide, sulphur dioxide and nitrogen dioxide (which are released into the air as pollutants) dissolve in rain drops to form carbonic acid, sulphuric acid and nitric acid respectively."

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.

Topic in NCERT: Soil treatment

Line in NCERT: "Organic matter releases acids which neutralises the basic nature of the soil."

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.

Topic in NCERT: Indigestion

Line in NCERT: "It neutralises the effect of excessive acid."

Milk of magnesia is an antacid.
Antacids are medicines that counteract (neutralise) the acid in your stomach to relieve indigestion and heartburn

- Lemon juice is acidic in nature because it contains citric acid, a weak organic acid that contributes to its sour taste.
- Soap solution is basic, as it contains alkaline substances like sodium hydroxide or potassium hydroxide.
- Slaked lime, or calcium hydroxide, is also basic and used to neutralize acids.
- Therefore, among the given options, lemon juice is the only one that is acidic.

Neutral solutions are substances that do not change the color of either red or blue litmus paper. This means they are neither acidic nor basic.

Topic in NCERT: Neutral Solutions

Line in NCERT: "The solutions which do not change the colour of either red or blue litmus are known as neutral solutions. These substances are neither acidic nor basic."

An ant bite injects formic acid, which is acidic. This effect can be neutralized by applying moist baking soda (sodium hydrogencarbonate) or calamine solution (zinc carbonate), both of which are basic and counteract the acidity.

Topic in NCERT: Ant bite

Line in NCERT: "When an ant bites, it injects the acidic liquid (formic acid) into the skin. The effect of the acid can be neutralised by rubbing moist baking soda (sodium hydrogencarbonate) or calamine solution, which contains zinc carbonate."

• The curd is produced due to the presence of reaction between lactic acid bacteria and the milk protein casein.
• When milk sugar or lactose undergoes fermentation, the product obtained is lactic acid.

Topic in NCERT: NATURAL INDICATORS AROUND US

Line in NCERT: "Lactic acid"

• When you put a drop of soap solution on turmeric paper, the paper turns red.
• This change in color happens because of a chemical reaction between the soap solution and the turmeric, showing that soap is a type of substance called a base.
• So, when soap solution comes in contact with turmeric paper, it changes the color to red.