CBSE Class 7 Science Acids Bases And Salts Worksheet Set 03

Question 1: Acids are sour–can you name two acids that you can actually eat to enjoy the sour taste?
Answer : In our daily diet, we usually have lactic acid from curd and citric acid from oranges, lemons to enjoy the sour taste

Question 2: Why are acids not stored in metal containers?
Answer : Acids are corrosive in nature. They can react with metals and corrode them, that's why acids are not stored in metal containers.

Question 3: Name two substances that have different colours in acidic and basic solutions. What is the general name for such substances?
Answer :  Phenolphthalein and methyl orange are the two substances which have a different colour in acidic and basic solutions. Phenolphthalein shows colourless in acidic and pink in basic solution. Methyl orange shows red in acidic and pink in basic solution. They both are commonly known as the indicator:

Question 4: In which reaction of acids is their acidic nature cancelled out to produce a neutral substance? What is the neutral substance called?
Answer :  When acids react with bases, their acidic nature is cancelled out. This type of reaction is called a neutralization reaction. The reaction of acids and bases produces a neutral substance known as 'salt'.

I. FILL IN THE BLANKS

Question 1. The word acid comes from the Latin word _________ which means sour.
Answer: acere
In simple words: The term acid originates from the Latin word 'acere', which translates to sour.

Exam Tip: Remember the Latin root 'acere' for acids and 'sour' taste association.

Question 2. _________ is the reaction between an acid and base.
Answer: Neutralization
In simple words: When an acid and a base combine, they neutralize each other's effects in a reaction called neutralization.

Exam Tip: Neutralization always produces salt and water along with heat.

Question 3. Substances which are neither acidic nor basic are called _________.
Answer: neutral
In simple words: Substances that do not show acidic or basic properties are termed neutral substances.

Exam Tip: Pure water and common salt solution are classic examples of neutral substances.

Question 4. _________ acid is found in vinegar.
Answer: Acetic
In simple words: Vinegar owes its sour taste and properties to acetic acid.

Question 5. Curd contains _________ acid.
Answer: lactic
In simple words: Milk turns into curd due to bacteria that produce lactic acid.

Exam Tip: Lactic acid is also produced in human muscles during vigorous physical exercise.

Question 6. The chemical name of lime water is _________.
Answer: calcium hydroxide
In simple words: Lime water is an aqueous solution of calcium hydroxide.

Exam Tip: Chemical formulas can be asked: calcium hydroxide is written as \(\text{Ca(OH)}_2\).

Question 7. Calamine solution contains _________ acid.
Answer: zinc carbonate
In simple words: Calamine lotion contains zinc carbonate which acts as a basic substance to neutralize ant stings (note: calamine contains a basic salt of zinc, often treated as a basic lotion).

Exam Tip: Calamine is applied to soothe insect bites because it is basic in nature and neutralizes acidic venom.

Question 8. Litmus is extracted from _________.
Answer: lichens
In simple words: Natural indicator litmus is obtained from plant-like organisms called lichens.

Exam Tip: Lichens belong to the division Thallophyta and have a symbiotic relationship between algae and fungi.

Question 9. Vitamin C is also known as _________.
Answer: ascorbic acid
In simple words: Vitamin C is chemically known as ascorbic acid and is found abundantly in citrus fruits.

Exam Tip: Ascorbic acid is essential for maintaining healthy skin, cartilage, teeth, and blood vessels.

Question 10. Complete the equation: Acid + base \(\longrightarrow\) _________ + water.
Answer: salt
In simple words: The reaction of an acid with a base always yields salt and water.

Question 1. All bases turn red litmus blue.
Answer: True
In simple words: Bases are characterized by their ability to change the color of red litmus paper to blue.

Exam Tip: Remember: Bases turn Red to Blue (BRB - Base Red to Blue).

Question 2. Neutral solution can change the color of litmus.
Answer: False
In simple words: Neutral solutions do not change the color of either red or blue litmus paper.

Exam Tip: Neutral solutions leave litmus paper color unaffected.

Question 3. A salt may be acidic, basic or neutral in nature.
Answer: True
In simple words: Depending on the strength of the reacting acid and base, salts can be acidic, basic, or neutral.

Exam Tip: Strong acid + weak base forms an acidic salt; strong base + weak acid forms a basic salt.

Question 4. Too much of base in stomach causes indigestion.
Answer: False
In simple words: Too much of acid (not base) in the stomach causes indigestion or acidity.

Exam Tip: We take antacids (which are bases) to neutralize excess stomach acid.

Question 5. Tartaric acid is present in spinach.
Answer: False
In simple words: Spinach contains oxalic acid, while tartaric acid is found in tamarind, grapes, and unripened mangoes.

Exam Tip: Match food items with their correct acids: Spinach = Oxalic acid, Tamarind = Tartaric acid.

III. NAME THE FOLLOWING

Question 1. An acid found in spinach.
Answer: Oxalic acid
In simple words: Spinach naturally contains oxalic acid.

Exam Tip: Oxalic acid is also found in tomatoes.

Question 2. Two natural indicators.
Answer: Litmus and Turmeric (or China rose)
In simple words: Indicators obtained from natural sources include litmus, turmeric, and China rose petals.

Exam Tip: Natural indicators help test whether a substance is acidic or basic without laboratory chemicals.

Question 3. Two artificial indicators.
Answer: Phenolphthalein and Methyl orange
In simple words: Indicators synthesized in laboratories are called artificial or synthetic indicators.

Exam Tip: Phenolphthalein remains colorless in acidic medium and turns pink in basic medium.

Question 4. A base found in soap.
Answer: Sodium hydroxide (or potassium hydroxide)
In simple words: Soaps are manufactured using strong bases like sodium hydroxide.

Exam Tip: Sodium hydroxide is commonly known as caustic soda.

Question 5. Two acids found in citrus fruits.
Answer: Citric acid and Ascorbic acid (Vitamin C)
In simple words: Citrus fruits like oranges and lemons are rich in citric acid and ascorbic acid.

Exam Tip: Citrus fruits are universally recognized sources of Vitamin C.

Question 6. Two pollutants in the air which causes acid rain.
Answer: Sulphur dioxide and Nitrogen dioxide
In simple words: Gases like sulphur dioxide and nitrogen dioxide dissolve in rain water to form harmful acids.

Exam Tip: These gases react with atmospheric moisture to form sulphuric acid and nitric acid.

Question 7. A base found in milk of magnesia.
Answer: Magnesium hydroxide
In simple words: Milk of magnesia contains magnesium hydroxide, which neutralizes stomach acid.

Exam Tip: Formula for magnesium hydroxide is \(\text{Mg(OH)}_2\).

Question 8. The acid present in the cell which controls every feature of the body?
Answer: Deoxyribonucleic acid (DNA)
In simple words: DNA is the genetic material present in cells that controls all hereditary traits and body functions.

Exam Tip: RNA (Ribonucleic acid) is another important nucleic acid in cells.

Question 9. Name an antacid.
Answer: Milk of magnesia (Magnesium hydroxide)
In simple words: Antacids are mild bases used to neutralize excess stomach acidity.

Exam Tip: Baking soda (sodium hydrogen carbonate) is also used as an antacid.

Question 10. Name the acid present in ant sting.
Answer: Formic acid (Methanoic acid)
In simple words: When an ant bites, it injects formic acid into the skin, causing pain and irritation.

Exam Tip: Rubbing moist baking soda (basic) or calamine solution relieves ant sting pain.

IV. CORRECT THE STATEMENT

Question 1. When the soil is basic it is treated with quick lime.
Answer: When the soil is acidic (not basic) it is treated with quick lime.
In simple words: Quick lime is basic in nature, so it is added to acidic soil to neutralize it.

Exam Tip: Basic soil is treated with organic matter (compost) which releases acids to neutralize it.

Question 2. In acidic solution phenolphthalein gives pink color.
Answer: In basic (not acidic) solution phenolphthalein gives pink color.
In simple words: Phenolphthalein remains colorless in acidic solutions and turns pink only in basic solutions.

Exam Tip: Acid = Colorless; Base = Pink with phenolphthalein.

Question 3. China rose indicator turns basic solutions to magenta color.
Answer: China rose indicator turns basic solutions to green (not magenta) color.
In simple words: China rose indicator turns acidic solutions to dark pink (magenta) and basic solutions to green.

Exam Tip: China Rose color change: Acid = Dark pink/magenta, Base = Green.

Question 4. Spinach contain citric acid.
Answer: Spinach contains oxalic (not citric) acid.
In simple words: Spinach is a rich source of oxalic acid, whereas citrus fruits contain citric acid.

Exam Tip: Always double-check acid names associated with specific vegetables and fruits.

V. CHOOSE THE CORRECT ANSWER

Question 1. Which one of the following doesn't causes acid rain?
(a) Carbon dioxide
(b) Calcium oxide
(c) Nitrogen dioxide
Answer: (b) Calcium oxide
In simple words: Carbon dioxide and nitrogen dioxide contribute to greenhouse effects and acid rain, whereas calcium oxide does not cause acid rain.

Exam Tip: Acid rain is primarily caused by emissions of sulphur dioxide and nitrogen dioxide.

Question 2. Which one of the following is acidic in nature?
(a) Vinegar
(b) Lime water
(c) Soap
Answer: (a) Vinegar
In simple words: Vinegar contains acetic acid and is acidic, while lime water and soap are basic.

Exam Tip: Sour-tasting substances are typically acidic in nature.

Question 3. Which one of the following is basic in nature?
(a) Curd
(b) Coffee
(c) Vinegar
In simple words: Since none of the given options (curd, coffee, vinegar) are basic, there is a printing error in the worksheet options. Curd contains lactic acid, coffee is slightly acidic, and vinegar contains acetic acid. (Standard answer key for this question designates basic substances; if lime water or soap were present they would be basic. Based on standard textbook sets, let us note the correct biological context: basic substances include soap and lime water).
*(Note: If strictly choosing among standard textbook examples, none are basic, but if this is an MCQ from a specific test, bases include antacids, soap, and lime water.)*

Exam Tip: Always identify bases by their bitter taste and soapy touch.

Question 4. Phenolphthalein remains color less in _________ solution.
(a) Acidic
(b) Basic
(c) Neutral
Answer: (a) Acidic (and also Neutral)
In simple words: Phenolphthalein stays colorless in both acidic and neutral solutions.

Exam Tip: Phenolphthalein is a synthetic indicator used to detect bases.

Question 5. Calcium hydroxide is called as _________.
(a) Quick Lime
(b) Lime Water
(c) Slaked Lime
Answer: (c) Slaked Lime (or Lime Water when dissolved in water)
In simple words: Calcium oxide is quick lime, while calcium hydroxide is known as slaked lime.

Exam Tip: Quick lime = Calcium oxide (\(\text{CaO}\)); Slaked lime = Calcium hydroxide (\(\text{Ca(OH)}_2\)).

VI. DEFINE

Question 1. Indicators
Answer: Indicators are special substances used to test whether a substance is acidic or basic. They change their color when added to a solution containing an acidic or basic substance.
In simple words: Indicators are substances that show different colors in acidic and basic mediums.

Exam Tip: Give examples such as litmus, turmeric, and phenolphthalein when asked to define indicators.

Question 2. Neutral solution
Answer: Solutions that do not change the color of either red or blue litmus are known as neutral solutions. These substances are neither acidic nor basic.
In simple words: A neutral solution has no acidic or basic properties and does not affect indicator colors.

Exam Tip: Pure water is the most common example of a neutral solution.

Question 3. Acid rain
Answer: Rain containing higher than normal amounts of acid, formed when pollutant gases like sulphur dioxide and nitrogen dioxide dissolve in rain drops, is called acid rain.
In simple words: Acid rain is polluted rain that contains dissolved acids harmful to buildings, plants, and aquatic life.

Exam Tip: Mention the pollutant gases (\(\text{SO}_2\) and \(\text{NO}_2\)) for full credit.

Question 4. Neutralization Reaction
Answer: The reaction between an acid and a base is known as neutralization. In a neutralization reaction, salt and water are produced with the evolution of heat.
In simple words: Neutralization is the process where an acid and a base cancel each other out to form salt and water.