CBSE Class 7 Science Acids Bases And Salts Worksheet Set B

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'.

Long Question/answers-

Question 5: Give two main uses each of (a) calcium hydroxide (b) ammonium hydroxide (c) sodium hydroxide
Answer : Two important uses of each base are stated below: (a) Calcium hydroxide [Ca(OH)2 1. It is used to whitewash buildings; it is also used as an alternative to cement in low-budgeted construction. 2. It is also used to neutralise the acidity of soil. Because of the over usage of chemical fertilisers, soil becomes acidic and hence largely affects the growth of crops. Thus, calcium hydroxide is added to the soil to neutralise its acidity, thereby ensuring the healthy growth of the crops. (b) Ammonium hydroxide (NH4OH 1. It is widely used to produce fertiliser like ammonium nitrate. 2. It is also used to produce nylons, plastics, dyes, etc. (c) Sodium hydroxide (NaOH): 1. It is extensively used in the production of soaps. 2. It is used to produce various medicines, rayon, paper, etc.

Question 6: State two methods by which salts can be prepared. Give one example of each.
Answer : Salts which are neutral substances can be prepared from the following methods: 1. Neutralization Reaction – It is the reaction between an acid and a base to produce salt, water and heat.
Example: Hydrochloric acid reacts with sodium hydroxide to produce sodium chloride (common salt), water and heat. The reaction is represented by the following equation: HCl +NaOH → NaCl + H2O 2. Reaction of metals with acids - Metals react with acids to replace hydrogen from the acids, thereby producing salts and liberating hydrogen gas. Example: Zinc reacts with dilute sulphuric acid to form zinc sulphate salt liberating hydrogen gas. The reaction is given below: Zn + dilH2SO4 → ZnSO4 + H2O

Question 7: What is soap? How can you make soap in the laboratory?
Answer : The sodium salts of acids are called soaps. A soap is prepared by boiling vegetable oil or fats from animals along with sodium hydroxide (NaOH). We can prepare a soap in the laboratory by following the below mentioned procedure. Required materials: 20ml of castor oil (we can also use coconut oil or any other oil) Half teaspoon of sodium hydroxide pellets 1 teaspoon of common salt (sodium chloride), and Glass rod for stirring Procedure :
• Take the 20ml castor oil in a beaker.
• Mix ½ teaspoon of sodium hydroxide pellets with about 20ml of water to prepare the sodium hydroxide solution.
• Now, mix the oil with the sodium hydroxide solution.
• Heat the mixture and allow it to boil for about 5 to 10 minutes by constantly stirring it with the glass rod.
The oil will react with the sodium hydroxide solution to form soap and glycerine.
Oil + Sodium hydroxide → Soap + Glycerine
• The soap formed can be separated from the mixture by adding a tea spoon of common salt (sodium chloride) in the beaker.
• After cooling, the solid soap gets separated from the mixture by floating on the top. Thus, a soap is prepared in the laboratory.

Question 8: How are salts named? Give two examples.
Answer : The name of a salt is derived on the basis of the reactants involved in its preparation. The salts are named after the metal supplied by the base and the radical supplied by the acid. Example 1: Sodium chloride (common salt) is formed from hydrochloric acid and sodium hydroxide. The name ‘sodium’ is supplied by the metal of the sodium hydroxide, and the name ‘chloride’ is supplied by the acid, which is a negative radical. HCl + NaOH → NaCl + H2O Example 2: Ammonium sulphate (salt) is formed from sulphuric acid and ammonium hydroxide. The name ‘ammonium’ is supplied by the ammonium radical of the base, while the name ‘sulphate’ is supplied by the negative radical of sulphuric acid. H2SO4 + NH4OH →( NH4)2SO4 + H2O

I.FILL IN THE BLANKS

1. The word acid comes from the Latin word _______________ which means sour.

2. _______________ is the reaction between an acid and base.

3. Substances which are neither acidic nor basic are called ________________.

4. ___________________ acid is found in vinegar.

5. Curd contains _______________ acid.

6. The chemical name of lime water is _________________.

7. Calamine solution contains________________________________.

II. WRITE TRUE OR FALSE

1. All bases turn red litmus blue.

2. Neutral solution can change the colour of litmus.

3. A salt may be acidic, basic or neutral in nature.

4. Too much of base in stomach causes indigestion.

5. Tartaric acid is present in spanich.

III. NAME THE FOLLOWING

1. An acid found in spinach.

2. Two natural indicators.

3. Two artificial indicators.

4. A base found in soap.

5. Two acids found in citrus fruits.

6. Two pollutants in the air which causes acid rain.

7. A base found in milk of magnesia.

IV. DEFINE

1. Indicators

2. Neutral solution

INTRODUCTION

♦ The earliest classification of inorganic compounds including the large number of organic compounds was based on their taste. On this basis of these compounds were classified into acid, bases and salt. We use many such compounds in our daily lives, which are acids, bases and salt. We use curd, pickle, amla, soap and detergents, tamarind, toothpaste etc. We must learn to classify them based on scientific tests.

♦ Test to distinguish between acids and bases
There are many substances, which show one colour or odour in the acidic medium and a different colour or odour in the basic medium. Such substances are called acid base indicators.

A. Indicators showing different colours in acidic and basic medium
a. Litmus solution as indicator is a purple coloured dye extracted from the lichen plant. It is the most commonly used indicator in the science laboratory. In the neutral solution, it has purple colour. In the acidic solution, it turns red whereas in the basic solution it turns blue. There are two types of litmus solution Blue and Red litmus solution. Red litmus solution is obtained by acidifying the purple litmus extract whereas blue litmus solution is obtained by making the purple litmus extract alkaline.
To test whether the given sample is acidic or basic, take few drops of distilled water in a test tube and two drops of blue litmus solution. Add few drops of sample substance that is to be tested. If the blue litmus solution changes into red colour, the substance is acidic. For instance, lemon juice, vinegar, orange juice, juice of unripe mangoes, tamarind all turn blue litmus solution to red. Thus, they are all acidic substances.
We may repeat the above experiment with red litmus solution. Those substances, which turn red litmus solution into blue colour, are bases. For instance, cucumber, washing soda solution, baking soda solution, bitter gourd etc. turn red litmus solution into blue. Thus, they are bases.
b. Synthetic indicators such as Phenolphthalein and Methyl orange

♦ Methyl orange is the compounds prepared industrially or in the laboratory. There are many such manmade substances, which can act as synthetic indicators.
♦ Phenolphthalein is colourless in neutral solution and in acidic solution but turns pink in basic solution.
♦ Methyl orange is of orange colour in neutral solution, red in acidic solution and yellow in basic solution.
Ask your teacher to help you classify various substance using these indicators.

B. Indicators giving different odours in acidic and basic medium. (Olfactory indicators)
♦ Clove oil
Take two test tubes. Mark them test tube ‘A’ and test tube ‘B’. Add some hydrochloric acid in test tube ‘A’ and some Sodium Hydroxide in test tube ‘B’. Record the odour, of clove oil. Now add few drops of clove oil in each test tube and shake it gently. Smell the sample in test tube ‘A’ and ‘B’. Record the odour of each test tube. You will notice that the odour of acid and base after addition of clove oil is different. Ask your teacher to help you demonstrate the experiment in the laboratory.

♦ Vanilla essence.
Repeat the experiment (a). Take another two test tubes and mark them ‘A’ and ‘B’. Add some acid ‘A’ and sodium hydroxide in ‘B’. Add some vanilla essence in each test tube (A) and (B). Vanilla retains its smell in acidic medium but looses its smell in basic medium.

C. Natural Indicators
Turmeric (Haldi), red cabbage, China rose peals are the natural indicators.
♦ Turmeric is yellow in colour. Turmeric leaves a yellow stain on clothes. When such stain is washed with detergents, the stain becomes brownish red. Detergents have the base called sodium hydroxide. This shows that the turmeric changes a base into brownish red colour. When the clothe is washed with lemon, it regains its yellow colour. This shows that brownish red colour of turmeric changes to yellow by acids.

♦ China rose petals act as a natural indicator. China rose indicator turns magenta (dark pink) in acidic solutions. It turns green in basic solutions and does not show any colour change in neutral solution

ACID

An acid (from the Latin acidus meaning sour) is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water. Chemicals or substances having the property of an acid are said to be acidic. Acids are sour in taste. Acids are of organic and inorganic nature. Acids found in plants and animals are organic in nature. Organic acids are weak whether inorganic acids are strong.

♦ Organic Acids

♦ INORGANIC ACIDS are called mineral acids. They are prepared by dissolving mineral oxides in water.
Sulphur dioxide dissolves in water to form sulphurous or sulphuric acid. Carbon dioxide dissolves in water to form carbonic acid. Hydrogen chloride dissolves in water to form hydrochloric acid etc.
a. Hydrochloric Acid
b. Nitric Acid
c. Phosphoric Acid
d. Sulphuric Acid.

PROPERTIES

♦ Acids are generally sour in taste. (For example, the sour taste of lemon juice is due to citric acid.)
♦ Strong or concentrated acids or their fumes often produce a stinging feeling on mucous membranes.
♦ Change the colour of pH indicators as follows: turn blue litmus and methyl orange red, turn phenolphthalein colourless.
♦ React with metals to produce a metal salt and hydrogen.
♦ React with metal carbonates to produce water, CO₂ and a salt.
♦ React with metal hydroxides and metal oxides to produce water and a salt.
♦ Conduct electricity, depending on the degree of dissociation in aqueous solution. Car batteries use acids in them.
♦ Acids can be gases, liquids, or solids. Respective examples (at 20ºC and one atm) are hydrogen chloride, sulphuric acid and citric acid. Solutions of acids in water are liquids, such as hydrochloric acid-an aqueous solution of hydrogen chloride. At 20ºC and one atm, linear carboxylic acids are liquids and solids beginning from decanoic acid (ten carbon atoms). Perfumed carboxylic acids, the simplest being benzoic acid, are solids.
♦ Strong acids and some concentrated weak acids are corrosive and can cause severe burns even after short contact.

BASES

Strong bases, like strong acids, attack living tissue and cause serious burns. They react differently to skin than acids do, so while strong acids are corrosive, we say that strong bases are caustic (corrosive). Bases may also be weak bases such as ammonia, which is used for cleaning. Arrhenius bases are watersoluble. An alkali is a special example of a base, where in an aqueous environment; hydroxide ions (also viewed as OH^–  are donated. Bases, which dissolve in water, are called alkalis. Bases are alkalis but not
all alkalis are bases.
The notion of a base as a concept in chemistry was first introduced by the French chemist Guillaume Francois Rouelle in 1754. He noted that acids, which in those days were mostly volatile liquids (like acetic acid), turned into solid salts only when combined with specific substances. These substances form a concrete base for the salt and hence the name.

PROPERTIES

Some general properties of bases include:
♦ Slippery or soapy feel on fingers, due to specification of the lipids in human skin
♦ Concentrated or strong bases are caustic (corrosive) on organic matter and react violently with acidic substances
♦ Aqueous solutions (bases dissolved in water) or molten bases dissociate in ions and conduct electricity
♦ Reactions with indicators: bases turn litmus paper blue and phenolphthalein pink
In chemistry, a base is most commonly thought of as an aqueous substance that can accept hydrogen ions. A base is also often referred to as an alkali if OH–  ions (hydroxide ions) are involved. Examples of simple bases are sodium hydroxide and ammonia. Although ammonia does not directly contain an OH– group in its, formula, it produces one in water i.e. Ammonium hydroxide. All compound containing hydroxide are bases. For example, Sodium hydroxide (NaOH), Potassium hydroxide (KOH), Magnesium hydroxide [Mg(OH)2], Calcium hydroxide [Ca(OH)₂] etc.
Bases can be thought of as the chemical opposite of acids. A reaction between an acid and base is called neutralization. Bases and acids are seen as opposites because the effect on an acid is to increase the hydronium ion (H3O⁺) concentration in water, whereas bases reduce this concentration. Bases react with acids to produce water and salts (or their solutions). Acids react with bases to form salt and water.
♦ Hydrochloric acid reacts with sodium hydroxide to form common salt called sodium chloride and water.
This reaction supports neutralization
♦ Farmers use slaked lime [calcium hydroxide, Ca(OH₂)] or quick lime [calcium oxide, CaO] to neutralise the acidic effects of soil in their farms.
♦ In case the soil is basic, organic matter is used to release or neutralise the bases.
♦ Bacterias are continuously produced in our mouth, which causes tooth decay by making acids. Basic nature of toothpaste and toothpowder prevents tooth decay by neutralizing the acidic effects.
♦ A small amount of hydrochloric acid available in our stomach helps digesting food and kills the germs. Its excess production in stomach causes indigestion. To neutralize the effects of acid magnesium hydroxide (milk of magnesia) tablets are used.
♦ Baking Soda [Sodium bicarbonate, NaHCO₃] is used to treat bee sting or ant sting. Their sting release formic acid on the skin is neutralized by bases.

SALT

A salt, in chemistry, is defined as the product formed from the neutralization reaction of acids and bases.
There are several varieties of salts. Salts that produce hydroxide ions when dissolved in water are basic salts and salts that produce hydronium ions in water are acid salts. Neutral salts are those that are neither acid nor basic salts.
When salts are dissolved in water, they are called electrolytes, and are able to conduct electricity, a property that is shared with molten salts. Sodium Chloride (NaCl), Magnesium Chloride (MgCl₂), Calcium Carbonate (CaCO₃), Calcium Sulphate (CaSO₄) etc. are some examples of salt. Not all salt are edible.
Salts can be poisonous to the body as well. Not all salts are salty. Salt that we add to our food is Sodium Chloride (NaCl).

(A) Choose the correct option.

Question. Acids are formed when
(A) metals combine with oxygen
(B) oxides of nonmetals dissolve in water
(C) metals react with water
(D) bases dissolve in water
Answer: C

Question. Hydrochloric acid can be neutralised by
(A) nitric acid
(B) sulphuric acid
(C) citric acid
(D) sodium hydroxide
Answer: D

Question. A soap solution is
(A) acidic
(B) alkaline
(C) neutral
(D) None
Answer: B

Question. In a neutralisation reaction, an acid reacts with a base to give
(A) another acid
(B) another base
(C) another acid and another base
(D) a salt and water
Answer: D

(B) Match the columns A and B
Question.    A                          B
(a) Hydrochloride acid (i) In storage batteries
(b) Ascorbic acid         (ii) Found in yoghurt
(c) Sulphuric acid       (iii) In making vinegar
(d) Lactic acid            (iv) As bathroom acid
(e) Acetic acid            (v) Vitamin C
Answer: (a) – (iv), (b) – (v), (c) – (i), (d) – (ii),(e) – (iii)

Question.    A                           B
(a) Sodium iodate             (i) A food preservative
(b) Calcium sulphate        (ii) Used as a fertiliser
(c) Bleaching powder       (iii) Present in plaster of Paris
(d) Ammonium sulphate   (iv) A disinfectant
(e) Sodium benzoate       (v) A supplement to common salt
Answer: (a) – (v),(b) – (iii), (c) – (iv), (d) – (ii), (e) – (i)

Q1. Choose the correct option:

1. The acid present in our stomach that helps in digestion of food is
(a) nitric acid
(b) acetic acid
(c) hydrochloric acid
(d) sulphuric acid

2. The soil is best for growing crop
(a) Sandy
(b) clayey
(c) loamy
(d) none of these

3. Acidic soil can be neutralised by adding
(a) vinegar
(b) lemon
(c) quicklime
(d) lactic acid

4.Cold drinks contain
(a) carbonic acid
(b) malic acid
(c) citric acid
(d) lactic acid

5.A soil that can hold less amount of water is
(a) clayey
(b) loamy
(c) sandy
(d) none of these

6. The darkest layer of soil is
(a) top soil
(b) bed rock
(c) C- horizon
(d) sub soil

7.Which of the following indicator give green colour in basic solution?
(a) Methyl orange
(b) China rose
(c) Phenolphthalein
(d)Turmeric

Q2.Complete the following analogy

a. Common salt: Neutral: : Vinegar : __________

b. Ant’s sting: Formic acid: : _____________: Lemon

Q3. One day Ritu got a wasp sting. Her mother advised her to apply some vinegar on the affected area.Why she has advised so?Also mention what are the qualities portrayed by her mother?

Q4. Aman conducted an experiment to calculate the rate of percolation. He observed that it took 40 minutes for 800 ml of water to percolate through the soil sample. Calculate the rate of percolation.

Q5. Enlist three agents that cause weathering of rocks?

I. Fill in the blanks:-

1. An acid is ____________ by a base .

2. Phenolphthalein is an __________ indicator.

II. Choose the correct option:-

1. A Soap Solution is –
a) Basic
b) Acidic
c) Alkaline
d) Neutral

2. CO₂ + H₂O →
a) Sulphuric acid
b) Nitric acid
c) Carbonic acid
d) None

III Name the following:-

1. Soluble bases.

2. A Chemical used as a food preservative.

3. Chemical name of Chile Salt Petre.

IV Define the following:-

1. Acid Rain

2. Neutralisation Reaction

3. Acid-Base Indicator

V Give Reasons:-

1. Non Metal Oxides are called Acidic .

2. Metal Oxides are Basic

3. Sour things are not kept in metal pots

4. Metal Oxides such as MgO are used for making refractory bricks.

VI Complete the Equations:-

1. ________ + 2O₂ → CO₂ + H₂O

2. 3NO₂ + H₂O → NO + _______ .

3. 2NaOH + H₂SO₄ → _________ + 2H₂O

4. CaCO₃ → ________ + CO₂

VII Answer in 20 words :-

1 Name three mineral acids and give their formulae?

2 What is acid and base?

VIII Answer in 40 words:-

1. What are general properties of bases?

2. What are general properties of acids?

3. Name an acidic gas which is discharged into the atmosphere on the burning of fuels like coal & natural gas. How is this gas formed?

IX Answer in 100 words:-

1. Describe an activity to show the effect of acid on carbonates and hydrogen carbonates?

2. What is acid rain? How is it formed? Mention three bad effects of acid rain .

X Write one use of the following:-

1. Sulphuric acid.

2. Citric acid

3. Sodium Carbonate

4. Potassium Nitrate

5. Calcium phosphate

Q1. Classify the following substances as acids and bases :

Tomato juice, tamarind juice, curd, toothpaste, soap solution, raw mangoes

Q2. Some acids, bases and salts are commonly used in our daily life. Find out the names of such substances, specify whether they are acids, bases or salts and write their uses.

Q3. What are mineral acids.? Give two examples.

Q4. Complete the table given below :

Name of the

Substance                    Type of acid Natural / mineral                   Source

Acetic acid

Fizzy drinks

Lactic acid

Citric acid

Tartaric acid

Formic acid

Q5. Write any two general properties of acidic substances.

Q6. Name any three mineral acids.

Q7. What happens when :

i). Magnesium is burnt in the presence of Oxygen and the product obtained is added to water

ii). An acid and a base is reacted.

iii). Blue litmus is added to vinegar.

iv). Lemon juice is added to baking soda

Q8. What are indicators? Give examples. Why do we use indicators?

Q9. What are neutral substances?

Q10. Ammonia is used in many household products like window cleaners. It turns red litmus to blue. What is the nature of ammonia?

Q11. What causes acidity in stomach? Why does a doctor recommend an antacid to a person suffering from acidity.

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1.Match the following:

(i) Grapes (A) Acetic Acid

(ii) Vinegar (B) Lactic Acid

(iii) Lemons (C) Tartaric Acid

(iv) Sour milk (D) Citric Acid

(A) (i)-(C), (ii)-(A), (iii)- (D), (iv)- (B)
(B) (i)-(B), (ii)-(A), (iii)- (D), (iv)- (C)
(C) (i)-(D), (ii)-(A), (iii)- (B), (iv)- (C)
(D) (i)-(B), (ii)-(C), (iii)- (D), (iv)- (A)

2.Give the names of two weak acids.

3.What is the chemical nature of a compound that turns blue litmus red?

4.Which base is found in window cleaner?

5.The reaction of acid and a base to form salt and water only is called-
(A) Neutralization.
(B) Addition.
(C) Substitution.
(D) Oxidation.

6.Solutions which do not change the colour of litmus are-
(A) Acidic.
(B) Basic.
(C) Neutral.
(D) Both (a) & (b).

7.When an acid and a base react with each other, the reaction mixture becomes-
(A) Hot.
(B) Cold.
(C) Acidic.
(D) Basic.

8.Acidpresent in the sting of an ant is....................
(A) Acetic acid.
(B) Formic acid.
(C) Lactic acid.
(D) Ascorbic acid.

9.China rose indicator turns acidic solution to ..................... and the basic solution to ..........................
(A) Dark pink, blue
(B) Red, yellow
(C) Dark pink, green
(D) Red, green

10.The acid present in our stomach which helps in digestion of food is-
(A) Sulphuric acid (H₂SO₄)
(B) Nitric acid (HNO₃).
(C) Hydrochloric acid (HCl).
(D) Phosphoric acid (H₃PO₄).

11.Why do some fruits taste sour?

12.Where is lactic acid found?

13.Name the acid which is found in our body cells.

14.The acid used for preserving food articles is-
(A) Acetic acid.
(B) Tartaric acid.
(C) Sulphuric acid.
(D) Nitric acid.

15.is known as ascorbic acid which is present in citrus fruits.
(A) Vitamin D.
(B) Vitamin C.
(C) Vitamin A.
(D) Vitamin K.

16.When a drop of phenolphthalein is introduced in lime water, the solution turns-
(A) Blue.
(B) Red.
(C) Milky.
(D) Pink.

17.Acids are ...................... in taste while bases are .................... in taste.
(A) Sweet, salty
(B) Sweet, sour
(C) Sour, salty
(D) Sour, bitter

18.Acid rain is caused due to ...................
(A) CO₂, O₂, SO₂
(B) CO₂, NO2, H2
(C) SO₂ N2, O₂
(D) CO₂, SO₂, NO₂

19.Natural indicator litmus is extracted from-
(A) Lichens.
(B) Earthworms.
(C) Ants.
(D) Algae.

20.The industrial waste is ................... in nature.
(A) Acidic
(B) Basic
(C) Neutral
(D) Both (a) & (b).

21.When turmeric stain on white clothes is washed with soap, it turns red in colour because-
(A) Soap solution is acidic.
(B) Soap solution is neutral.
(C) Soap solution is basic.
(D) Both (a) & (b).

22.Milk of magnesia used to treat acidity in stomach, contains this base.
(A) Magnesium hydroxide.
(B) Ammonium hydroxide.
(C) Sodium hydroxide.
(D) Copper hydroxide.

23.The substances used to test the acidity and basicity of substances are called-
(A) Indicators.
(B) Testers.
(C) Analyzers.
(D) All of them.

24.Citrus fruits contain-
(A) Ascorbic acid.
(B) Oxalic acid.
(C) Citric acid.
(D) Both (a) and (c).

25.Which acid is present in our stomach?
(A) Hydrochloric acid (HCl).
(B) Sulphuric acid (H₂SO₄).
(C) Nitric acid (HNO₃).
(D) None of the above.

26.Lactic acid is found in-
(A) Milk.
(B) Curd.
(C) Vinegar.
(D) Tamarind.

27.All sour substances are acidic in nature.
(A) Yes.
(B) No, they are basic.
(C) No, they are neutral.
(D) Sometimes, they may be acidic and sometimes basic.

28.How can you remove the acidity of soil ?

29.are used to identify the nature of substances.

30.Bases are to taste and acids are to taste.

31.Antacid tablets contain which neutralise the excess acid formed in our body.

32. is the reaction between acid and base to form salt and water.

33.if china rose indicator is added to acidic solution, it turns and when added to basic solution, it turns

34.lime water contain the chemical __________

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35.Why is factory waste neutralized before disposing it into the water bodies?

36.Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution?

37.Give reason- An antacid tablet is taken when you suffer from acidity.

38.Define indicators.

39.What is a salt? How are salts classified?

40.What are neutral substances? Give two examples

41.Why should we take great care while handling laboratory acids and bases?

42.Where is neutralization used in daily life?

43.Define acids. Give two examples.

44.Define bases. Give two examples.

45.Define bases. Give two examples. <$>

46.What are indicators ? Give any two examples

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47.What do you understand by acid rain? Write disadvantages of it.

48.What are natural indicators? How to they behave with acid or base?

49.What are Laboratory indicators? How do they behave with an acid

50.What makes a soil acidic? How is soil treated if it is too acidic or too basic?

51.John has a few bottles of soft drink in his restaurant. Unfortunately, these are not labelled. One customer wants acidic drink, another wants basic and third one want neutral drink. How will John decide which drink is to be served to whom?

52.Why is Calamine solution applied on the skin when an ant bites.

53.How is litmus obtained? What is the use of it?

54.What is acid rain ? What are its ill effects ?

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55.Three liquids are given to you. One is hydrochloric acid; another is sodium hydroxide and third is a sugar solution. How will you indentify them? You have only turmeric indicator.

56.Write the diffrences between Acids and bases

57.Explain the process of Neutralization. Give an example

58.List any Five acids that occur in nature and write their source.

59.List any Four bases that occur in nature and write their source.

60.Differentiate between acids and bases.

Q.1 Complete the following:-
(i) The sour things we eat contain __________
(ii) Ammonium hydroxide is __________
(iii) An acid is __________ by a base
(iv) Milk contains ______ acid.
(v) Litmus is extracted from __________

Q.2 Multiple choice questions (Choose the correct option)

(A) Which of the following is a strong acid?
(a) Nitric acid
(b) Citric acid
(c) acetic acid
(d) Tartaric acid

(B) which of the following is not a base?
(a) Sodium Hydroxide
(b) Magnesium Hydroxide
(c) Copper Carbonate
(d) Ammonium Hydroxide

(C) Which of these metals can not be used to prepare hydrogen by the action of an acid.?
(a) Sodium
(b) Iron
(c) Zinc
(d) Copper

(D) what is the common name of Sodium bicarbonate?
(a) Phitkari
(b) Caustic Soda
(c) Baking Soda
(d) Blue vitriol Non renewable and can not be recycled

(E) Sodium chloride will turn
(a) Blue Litmus Red
(b) Methyl orange yellow
(c) Red Litmus blue
(d) None of these

Q.3 Name one each of acidic, basic and neutral substances.

Q.4 What are the general properties of an acid and a base?

Q.5 What is an indicator? Give examples of two natural indicators?

Q.6 What is an acid rain? How is it formed? Mention three bad effects of acid rain.

Q.7 Name four substances that can serve as indicators.

Q.8 ‘Turmeric indicator does not indicate whether the substance is acidic or neutral. Is the statement true? Explain.

Q.9 What is the color of litmus paper which changes its color in acidic solution?

Q.10 If few drops of purple-cabbage juice are added to the colorless solution of an acidic material. What would be the color of the resulting solution?

Q.11 A few drops of china rose indicator are added to the colorless solution of a chemical the resulting solution will become light green. What does it indicate about the nature of the chemical?

Q.12 What is a neutralization reaction? Does a neutralization reaction always result in the formation of neutral salt?

Q.13 Write a note on uses of bases.

Q.14 You are given three unknown liquids an acid other is a base and third is a neutral substance. How will you classify the given liquids as acidic, basic and neutral?

Q.15 An acidic material is mixed with an equivalent amount of a basic material.
(i) What is the reaction called?
(ii) What products are formed?

Q.16 Explain why
(i) Great care should be taken while handling Laboratory acids and bases.
(ii) Acidic soil is treated with a base and basic soil is treated with organic matter.

Q.17 How is a salt formed?

Q.18 What happens when metals and non-metals combine with Oxygen?

Q.19 Nancy a class-VII student was performing an experiment in the Chemistry lab. Her teacher instructed her
1) Not to waste/smell chemicals
2) Not to dispose off all chemicals in the sink.
3) Not to mix chemicals haphazardly for example, never add water to acid to
dilute it; always add acid slowly to water.
Why did the teacher advice Nancy to follow the above safety measures?

HOTS QUESTIONS

Q.1 If you get Turmeric stain on your clothes while eating food, and try to wash it off with soap, the stain becomes red. Why? Find out how to remove haldi stains from clothes.

Q.2 Is the meaning of ‘weak acid’ the same as that of dilute acid?

Q.3 The waste of many factories contain acids. Why is it considered necessary to neutralize them before allowing the waste to flow into water bodies.?

Fill in the blanks :

1. Spinach contains_____________ acid while tamarind contains ________________ acid.

2. The gas which escapes out from many aerated soft drink is _____________

3. Carbon burns in air to form _______________

4. The chemical name of lime water is ______________

5. _______________ is the reaction between an acid and base.

6. An aqueous solution of sodium oxide changes ________________ litmus to blue.

7. Phenolphthalein indicator turns acidic solutions to ______________ and basic solutions to _____________.

8. The chemical name of moist baking soda is _____________

9. Calamine solution contains __________________( a base ).

10.Litmus is obtained from the _____________________

11.Curd contains __________ while vinegar contains ___________

Complete the following word equations :

1. Zinc + hydrochloric acid ___________+ _____________

2. Sodium hydroxide + Hydrochloric acid ___________+ ________

3. Calcium hydroxide + sulphuric acid _____________+ ________

True or False :

1. All acids turn blue litmus red. True / False

2. Neutral solution can change the colour of litmus. True / False

3. Orange juice turns blue litmus red. True / False

4. Substances which are neither acidic nor basic are called neutral. True/ False

5. An acid and a base neutralize each other and from a salt. True / False.

6. China rose indicator turns acidic solution to green. True / False

Name the following :

1. Two natural indicators.

2. One artificial indicator

3. Two pollutants in the air which causes acid rain.

4. Two substances which can neutralize an ant’s bite.

5. Two acids found in citrus fruits.

Define
1. Indicators
2. Neutral solution

Short Question/answers-

Question 1: What is an acid-base indicator? Give one example.
Answer : Acid-base indicators are special substances which are used to detect the acidity or basicity of other substances. The changes in colour of the indicators help us in understanding which substance is acidic and which one is basic. Example: Litmus paper is a natural acid-base indicator.

Question 2: Name one each of acidic, basic and neutral substances.
Answer : Acidic substance: Lemon juice is an acidic substance, as it contains citric acid. Basic substance: Baking soda is basic in nature, as it contains sodium bicarbonate. Neutral substance: Common salt is a neutral substance, as it is made of sodium chloride.

Question 3: What happens when dilute sulphuric acid is added to zinc?
Answer : Zinc will react with dilute sulphuric acid to form zinc sulphate salt and hydrogen gas. The reaction is given below: Zn + H₂SO₄ → ZnSO₄ + H 

Question 4: How can carbon dioxide be prepared from an acid?
Answer : Metal carbonates react with dilute acids to form salt, water and carbon dioxide gas. Thus, carbon dioxide can be prepared by reacting any metal carbonate with any dilute acid. Example: Carbon dioxide gas is liberated when sodium carbonate reacts with dilute hydrochloric acid. Na₂CO₃ + 2HCl →2NaCl + H₂O + CO₂

Question 5: Give two examples each of strong acids and weak acids.
Answer : Examples for strong acids: Sulphuric acid and nitric acid. Examples for weak acids: Citric acid (present in citrus fruits) and acetic acid (vinegar).

Question 6: Why does a base applied to your skin give relief from an ant bite?
Answer : While biting, insects inject formic acid into the skin. This causes irritation to the skin, and sometimes results into rashes. To get relief from this, a base like baking soda is applied over the bitten area. As bases neutralize acids, the baking soda (being a base) will neutralize the injected formic acid, thereby reducing the irritation. Thus, a base should be applied to the skin to get instant relief from an ant bite.