Science 2 Marks Questions

Natural indicators can be made using plant materials with pigments that change colour with acid or base. For example, to make red rose extract :
1. Wash and crush rose petals.
2. Place them in a glass tumbler and add hot water.
3. Let it sit for 5-10 minutes, then filter the mixture.
The resulting liquid is a natural indicator that turns red in acids and green in bases.

Keerthi’s grandmother can reveal the secret message by using acid-base indicators, as orange juice is acidic in nature. She can use rose extract or beetroot juice (which will turn red) or Indian blackberry extract (which will turn pink) to make the message visible.

When baking soda (a base) is added to the mixture of grape juice and red rose extract, the basicity increases. In basic conditions, red rose extract turns green. So, after adding baking soda, the mixture will turn green.

Manya should use an olfactory indicator to test the solutions. Olfactory indicators change their smell in acidic or basic solutions. For example, substances like onion produce a strong smell in a basic solution and a mild smell in an acidic solution.

If the extract of red rose turns the liquid X to green, it indicates that liquid X is basic. Red rose extract acts as an indicator, turning red in acidic solutions and green in basic solutions. When excess amla juice (which is acidic) is added to liquid X, it will neutralise the base. The green colour of the liquid will turn to red as the solution becomes more acidic due to the addition of the acidic amla juice.

Using turmeric paper, we can identify a basic solution but not an acidic or neutral solution. When baking soda solution (basic) is tested, the turmeric paper will turn red. However, both vinegar (acidic) and sugar solution (neutral) will leave the paper yellow, as turmeric paper does not change colour in acidic or neutral solutions. Therefore, turmeric paper can only identify a basic solution.

(iii) The solution turns from red to blue, it means it is basic. To reverse this, an acid is needed. Lime water and baking soda are basic, and the common salt solution is neutral, so they will not reverse the change. Vinegar is acidic, so it will change the colour back to red.

Acids and bases are two types of substances with different properties. Acids are substances that taste sour and turn blue litmus paper red. They can be strong or weak. Some common acids are lemon juice (contains citric acid), vinegar (contains acetic acid), curd (contains lactic acid), and tamarind (contains tartaric acid). Bases are substances that taste bitter and feel soapy to touch. They turn red litmus paper blue. Bases can also be strong or weak. Some common bases are soap, baking soda, and lime water.

(i) It can be identified on the basis of the following observations: Bases change the colour of Red litmus paper to blue. As the colour of blue litmus paper is not affected, the solution must be basic.
(ii) If the solution is neutral, even then the colour of litmus will not change. Hence, the solution may be basic or neutral.

The substances which are used to test whether a substance is acidic or basic are called indicators.
There are two types of indicators:
(i) Natural indicators : Litmus paper, turmeric, etc.
(ii) Synthetic indicators : Phenolphthalein

Red and blue litmus paper strips are made from paper soaked in an extract of lichens. They change colour when they come in contact with acidic or basic substances. Acidic substances turn blue litmus to red, and basic substances turn red litmus to blue.

The common acids present in the fruits in the basket are:
Citric acid – found in oranges, lemons, and other citrus fruits
Tartaric acid – found in grapes
Malic acid – found in apples

(a) The substance used is a base (alkaline substance)
Explanation: Turmeric paper is yellow in neutral or acidic solutions, but it turns red in the presence of a base. This red discoloration shows that the substance is basic in nature.
(b) The substance is basic (alkaline).
This can be confirmed using other indicators:
Litmus paper: turns blue in a base.
Red rose extract: changes colour in a basic solution.

Turmeric acts as an indicator, changing color in response to acids or bases. Soap is basic, so when turmeric is sprayed on a soap message, the turmeric turns red due to the basic nature of the soap, revealing the message.

Factory waste can be acidic and harm the environment, especially aquatic life. Treating the waste neutralizes it, making it safer to release into the environment.

(1) Red Cabbage:Chop red cabbage and boil in water.
(2) Turmeric:Mix turmeric powder with a little water to make a paste.
(3) Red Rose Petals:Collect red rose petals and soak them in hot water.

 The gardener should use acidic soil.

Use litmus paper: Red indicates acid, blue indicates base.
Turmeric turns red in bases.
Red rose extract turns red in acids and green in bases.

When an acid reacts with a base in a neutralization reaction, the primary products formed are salt and water.
The reaction also releases heat, indicating an energy change as the acid and base combine to form new substances with different properties.

When we don't have litmus paper, we can use turmeric or red rose petals from our kitchen to test if something is an acid or a base.
Example: we can make turmeric paper by mixing turmeric powder with water and applying it to paper. If we put a drop of a substance on the paper and it turns red, the substance is basic.
These kitchen materials act as natural indicators to identify acids and bases.

The presence of a bitter taste doesn't automatically classify a substance as a base.Bitterness can arise from various chemical compounds that are not necessarily alkaline or basic in nature.
Example:bitter gourd (karela) has a distinctly bitter taste due to compounds present in it, but it is not basic.

(1) Acidic substances: Turn blue litmus paper red.
(2) Basic substances: Turn red litmus paper blue.

 (1) Sugar solution
(2) Salt solution

When an ant bites, it injects an acidic liquid called formic acid into the skin, which causes pain and irritation. Baking soda is a base, and when it is applied to the affected area, it neutralizes the formic acid. This neutralisation reaction reduces the pain and provides relief.

In acidic solutions, red rose extract gives a red colour. In basic solutions, red rose extract gives a green colour.

(1) Litmus:It is obtained from lichens.
(2) Red Rose:Extract gives red colour in acidic solutions.
(3) Turmeric:The yellow colour of turmeric turns red in basic solutions.

It is a reaction where an acid and a base mix to form salt and water.The resulting solution is neither acidic nor basic.
Example: When an ant bites, it injects an acidic liquid (formic acid) into the skin.Rubbing moist baking soda (a base) neutralises the effect of the acid, relieving the pain.

Neutralisation helps in treating ant bites, balancing soil for farming, treating factory waste and even controlling acidity problems in the stomach with antacids. It protects both living beings and the environment​.

Vinegar is acidic and reacts with the calcium carbonate in eggshells, producing carbon dioxide gas. This causes the bubbles. Soap solution is basic and does not react​.

Baking soda turns turmeric paper red (basic). Vinegar and sugar solution do not change turmeric paper colour. Among them, vinegar will taste sour (acidic) and sugar solution will taste sweet (neutral)​.

By changing the soil’s pH. Making the soil more acidic by adding organic matter makes flowers blue; making it basic by adding lime turns flowers pink or red​.

Ashwin coated paper with turmeric paste and used a soap solution to write the message. When sprayed with water or acid, the letters appeared in a different colour​.

Unknown substances might be harmful or poisonous. To stay safe, students must avoid tasting anything unless clearly instructed by the teacher during science experiments.

Hydrangea flowers turn blue in acidic soil and pink or red in basic soil. Gardeners can adjust soil acidity or basicity to change the colour of the flowers​.

Turmeric changes colour only in the presence of a base (turning red). It doesn’t show any change with acidic or neutral substances. Therefore, turmeric can only detect basicity, not acidity​.

Factories sometimes release acidic waste into lakes, harming aquatic life. Before releasing, the waste can be treated with basic substances to neutralise it. This protects fish and other organisms living in the water​.

If soil becomes too acidic, lime (a base) is added to neutralise it. If soil is too basic, organic matter like compost is added. Maintaining soil’s pH balance is important for healthy plant growth and good nutrient availability​.

The ant injects formic acid during a bite. Baking soda, being a base, neutralises the acid and relieves the stinging pain.

When an acid reacts with a base, they neutralise each other to form salt and water, along with the release of heat​.

Turmeric is made into a paste and applied on paper strips. In basic substances, turmeric paper changes from yellow to red, but it stays yellow with acidic and neutral substances​.

Red rose extract gives a red shade in acidic solutions and a green shade in basic solutions. It remains unchanged with neutral substances, making it a natural acid-base indicator​.

Group A substances turn blue litmus red (acidic), Group B substances turn red litmus blue (basic) and Group C substances do not affect either (neutral). This helps classify substances easily​.