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Wednesday, April 18, 2018

Structure of Matter class07

The language of chemistry class 7 Basic science soled questions.

Q. What is chemistry?
Ans: Chemistry is a branch of science in which we study the composition, structure, properties and change of matter.

Q. What is matter?
Ans: Anything that is around us having some mass and occupies space is called matter.

Q. What are the different classifications of matter?
Ans: Matters are classified into element, compound and mixture.

Q. What is element?
Ans: Elements are the purest form of substance (matter) made up of same kinds of particles. The smallest unit of element is an atom. eg. Hydrogen, oxygen, carbon.

Q. What is compound?           

See full post  The language of chemistry class 7 Basic science

Class 07 Basic sciences Chapter the Language of Chemistry
A. Answer these questions

1. What does the formula of a substance tell us?

Answer: Formula of a compound or an element represents the name and number of atoms present in one molecule of that compound or element.

2. What do you mean by valancy of an element?

Answer: The number of electrons that can be donated, accepted or shared by an atom of an element during a chemical reaction is equal to the valency of that element. Thus the combining capacity of an atom is called its valancy.

3. What is a radical?

Answer: A compound radical is a group of two or more elements that acts as a single atom in a chemical reaction.
4. Name two elements having variable valancy. Give the name and formulae of compounds formed byeach of these element.

Answer: Two elements having variable valency and compounds formed by them are as follows:

(i) Copper (Cu):  
(a) Cuprous oxide [Copper (I) oxide] − Cu2O     
 (b) Cupric oxide [Copper(II)oxide] − CuO

(ii) Iron (Fe):  (a) Ferrous oxide [Iron(II)oxide] − FeO                    
(b) Ferric oxide [Iron(III)oxide] − Fe2O3

5. What is balance equations? Why should a  equation be balanced?

Answer: A reaction is in which the number of atoms on the side of the products is equal to the number of atoms on the side of the reactants is called a balanced chemical. This is known as law of the conservation of mass given by Antoine Lavoisier's 1789.  We balance a chemical reaction to represent this fact.

B. Find the vacancies of the underlined element or radicals in the following compound?


Valency of Underlined
Valency of Underlined
Valency of Underlined
Valency of Underlined

C. What are compound radicals? Give examples of a few radicals, along with their valancies. Also mention some compound containing compound radicals. Give the valancies of the part that make up the compound?

Answer: Compound radical is a group of atoms of different elements that behave as an intact unit during a chemical reaction. Atoms in a compound radical do not break apart revealing the individual atoms but remain together forming an intact group of atoms having a valency. This unit behaves just like an atom or a molecule during a reaction.
Some compound radicals with their valencies are given below:

Compound Radical        Valency
OH                               1
SO4                              2
NO3                              1
CO3                              2

Some compounds containing compound radicals:

Compound Radical
Sodium hydroxide
Sulphuric acid
Sodium carbonate
Ammonium sulphate
 Potassium nitrate

D. Complete the following

Answer :

1. A symbol is an abbreviation of the name of an element.
2. A molecule of an element or a compound is represented by its formula.
3. The valencies of the two elements of a binary compound are transposed to obtain its formula.
4. Atoms are neither lost nor gained in a chemical reaction.
E.Choose the correct options
1. Which of the following is the symbol of gold?
C. Au   
2. Which of the following is a divalent radical                                                      
(c) Sulphate                 
3. The vaancy of sulphur in sulphur dioxide                                                       
 (d) 4                
4.How many times greater is the valency of N in NH3 than that of Cl in HCl          
(b) 3
Valency of N in NH3 is 3, whereas the valency of Cl in HCl is 1.  
Hence, the valency of N in NH3 is three times greater than that of Cl in HCl.

F. Match the coloumn

Answer :

Column A
Column B
(a) Helium
(ii) He
(b) Mercury
 (i) Hg
(c) Copper
(v) Cu
(d) Calcium
(vi) Ca
(e) Phosphorus
(iv) P
(f) Lead
(iii) Pb

G. Say true and false

Answer :

1. True. The valency of hydrogen is 1.
2. True. The valency of oxygen is 2.
3. False. Symbol of iron is Fe.
4. True. The symbol of silver is Ag.
5. False. Calcium chloride is CaCl2.
6. True. The valency of both zinc and oxygen is 2. So, zinc oxide is ZnO

H. Write the formula of following compound

Answer :

Calcium oxide
Carbon dioxide
Carbon monoxide
Magnesium oxide
Hydrogen chloride
 H Cl
Sodium chloride
Potassium chloride
Magnesium chloride
Zinc chloride
Nitric acid
Sodium nitrate
Sodium carbonate
Potassium carbonate
Calcium carbonate

CBSE Class 7 Solved Objective Questions Chapter - Acids, Bases and Salts MCQs

CBSE Class 7 Solved Objective Questions Chapter - Acids, Bases and Salts MCQs

1. The word acid comes from the Latin word ------ which means sour.( acere)

2. The substances used to test whether a substance is acidic or basic are known as ----(indicators)

3. The most commonly used natural indicator is litmus paper . It is extracted from ----(lichens)

4. In acidic solution, litmus paper turns into ------(red)

5. In basic solution, litmus paper turns into ------(blue)

6. In distilled water , litmus paper turns into ------(purple)

7. China rose indicator turns acidic solutions ------and basic solutions to ------

[dark pink (magenta) , green]

8. The reaction between an acid and a base is known as ----- [neutralization]

9. Salt and water are produced in neutralization process with the evolution of heat.[ water]

10. HCl + NaOH ----> ------- +  H2 [NaCl]

11. Our stomach contains -------. It helps us to digest food[hydrochloric acid]

12. indigestion is painful so to relieve indigestion, we take an antacid such as milk of magnesia , which contains ------ [magnesium hydroxide]

13. The sting of an ant contains ---------[ formic acid]

14. The effect of the sting can be neutralized by rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution, which contains ------- [zinc carbonate]

15. When the soil is too acidic, it is treated with ---------------[ bases like quick lime (calcium oxide) or slaked lime (calcium hydroxide)]

16. Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. its nature ---------------------- [Basic]

17. The wastes of many factories contain-------- [ acids]

18. Blue litmus paper is dipped in a solution. It remains blue. -------- is the nature of the solution. [basic]

19. Proteins that build part of our cells are made up of------ [amino acids]

20. The fats in our body contain ------ [fatty acids]

21. Each cell in our body contains an acid called ---------- [the deoxyribonucleic acid]

22. ----------- is  common to all acids?[hydrogen ion]

23. ------ gas evolved when dilute sulphuric acid acts on sodium carbonate[CO2]

24. Acids do not show acidic behavior in absence of water because ------ dissociates from an acid only in the presence of water. [ hydrogen ions]

25. ---- base is also used in soda-acid fire extinguishers.[ Baking Soda]

26. -------- gas is usually liberated when an acid reacts with a metal [ H2]

27. The hydrogen ions combine with H2O to form ------------- [ hydronium ions (H3O+)]

28. Aqueous solution of acid conduct electricity due to -------- present in it. [ ion]

29. ------------ is the common name of the compound CaOCl2 [Bleaching powder]

30. -------------- is Universal Indicator [ pH Scale]

31. pH is the measure of Acidity or Alkalinity of a solution. The term pH stands for ----------[“Potential of hydrogen”]

32. If the pH rain water drops below ----------------. it is called acid rain[5.6]

33. The bases that dissolve in water are known as -----------[ alkalies]

34. Aqueous solution of sodium chloride (NaCl) is known as -------------[ Brine]

35. Salts containing water molecules in their crystal form are called --------- [hydrated salts]

36. water molecules present in salt s known as ------------ [‘water of crystallization’]

37. Phenolphthalein become colourless in ---- and pink in ------[ Acid, base]

38. --------- is the colour of methyl orange in acidic solution.[ pink]

40. ------------ and ------- acid are present in vinegar and lemon.[ acetic acid, citric acid]
chemistry adda: CBSE Class 7 Solved Objective Questions
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CBSE Chemistry 7th Acids bases and Salts [Solved]

Read Full Post: 7th Acids bases and Salts [Solved]

Q1. What are acids?

Ans. Acids are the substances which are sour in taste.

Q2. What are bases?

Ans. Bases are the substances which are bitter in taste & soapy to touch.

Q3.Give examples of acids and bases.

Ans. Acids- hydrochloric acid, acetic acid, citric acid, lactic acid etc

Bases- baking soda, sodium hydroxide, soap etc

Q 4. Name the acids present in the following substances.

acetic acid
lactic acid                                
oxalic acid
citric acid                                  
citric acid
tartaric acid

Q5. What are indicators? Give examples.

Ans. Indicators are the special type of substances which are used to distinguish between acids & bases by showing colour changes.

Example: litmus, turmeric, beetroot, China rose extract, phenolphthalein etc.

Q6.Name the source from which litmus is obtained.

Ans. Litmus is obtained from a plant lichens.

Q7. in what forms is litmus available?

Ans. Litmus is available in the form of solution or in the form of strip of paper.

It is available as red & blue litmus.

Q8. Why do we use indicators?

Ans. We use indicators to find out whether a substance is acidic, basic or neutral, as all the substances can’t be tasted. Some of the substances are highly corrosive and hence can be harmful to us if tasted.

Q9.What happens when phenolphthalein is added to  (a) Acidic solution (b) basic solution (c) Neutral solution

(a) in acidic solution, the colour of phenolphthalein remains colourless.

b) When phenolphthalein is added to basic solution, the colour changes to pink (magenta).

c) In neutral solution, it remains colourless.

Q10.What are neutral substances?

Ans. The substances which are neither acidic nor neutral are known as neutral solutions.

Q11. What happens when a base is put on turmeric paste? What will happen when acid is added to the same?

Ans. When base is added to turmeric paste, then its colour changes to red. If we put an acid on the same then changes to yellow again.

Q12. How will you identify weather a substance is acidic or basic using red & blue litmus?

Ans. Acids & bases can be distinguished using litmus solutions as follows:

- if the colour of red litmus changes to blue, then the substance is basic in nature.

- if the colour of blue litmus changes to red, then the substance is acidic in nature.

Q13. Ammonia is used in many household products like window cleaners. It turns red litmus to blue. What is the nature of ammonia?

Ans. As ammonia turns red litmus to blue that shows it is basic in nature.

Q14. What is the effect of China rose indicator on acidic & basic solutions?

Ans. China rose indicator turns acidic solutions to dark pink and basic solutions to green.

Q15.What is neutralization reactions?

Ans. The reaction in which an acid & a base react to form salt and water, with the evolution of heat is known as neutralization reaction.

Acid + base ------> salt + water.

Hydrochloric acid + sodium hydroxide --> sodium chloride + water

Q16. What are salts? Are they acidic, basic or neutral?

Ans. Salts are substances formed by the reaction of an acid and base. Salts can be acidic, basic or neutral.

Q17. What are antacids?

Ans. antacids are the medicines that arte use to relieve from acidity in stomach. Example: milk of magnesia, eno etc.

Q18 what causes acidity in stomach?

Ans. Our stomach contains hydrochloric acid which helps us to digest food. When the amount of acid present in stomach increases, it leads to acidity.

Q19 How is antacids helpful in relieving indigestion?

Ans. Antacids are basic in nature, hence they neutralize the effect of excess of acid and relieve us from indigestion.

Q20. Why is calamine solution put on the ant sting?

Ans. When an ant bites, it injects formic acid into the skin. The effect of acid can be neutralized by applying calamine solution which is basic in nature.

Q21.Sometimes we treat the soil with bases. Give reasons why?

Ans. Excessive use of fertilizers makes the soil acidic, which is not suitable for the growth of the plants .Hence we treat the soil with bases like calcium oxide to neutralize of acid.

Q22.The factory waste is treated with basic substances before disposing it?

Ans. The wastes of factories contain acids. If they are allowed to flow into the water bodies, then they are harmful to the aquatic life. Therefore, factory waste are treated with basic solutions.

Q23.What is the chemical name of the following:

Common name
Chemical name
Quick lime
Calcium oxide
Slaked lime
calcium hydroxide
Baking soda
sodium hydrogen carbonate

Q24. What is the chemical composition of milk of magnesia?

Ans. The chemical composition of milk of magnesia is magnesium hydroxide.

Q25. What is the chemical composition of calamine solution?

Ans. The chemical composition of calamine solution is zinc carbonate.

Related study materials
MCQ:Acid base and salt: For Olympiads-1 
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MCQ:Acid base and salt: For Olympiads-2
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CBSE Class-7th Science Fibre to Fabric

CBSE _ NCERT Class-7th Science  Chapter: Fibre to Fabric

Why a cotton garment cannot keep us as warm in winter?
Cotton clothes are thin and do not have spaces in which air can be trapped. thus Cotton clothes do not prevents heat coming out of our body.
What is a fibre?

A fibre is a long strong thread, which is obtained from natural sources or man made sources.
Fibres are classified into two types on the basis of their sources. Plant fibres and animal fibres and synthetic fibres.

The fibres, which are obtained from plants and animals are called natural fibres e.g., jute and wool.
Animal fibres are obtained from animals, e.g., silk and wool.

Those fibres which are made by the human –beings are known as Man-made or Synthetic Fibres, e.g., Rayon.

Match the following:
1. Scouring-->          Cleaning sheared skin
2. Mulberry leaves-> Food of silkworm
3. Yak ->                  Wool yielding animal
4. Cocoon ->             Yields silk fibers.
Explain the process of making yarn from fiber ?

The process of making yarn from fiber is called spinning. In this process,fibers from a mass of cotton wool are drawn out and twisted. this brings the fibers together to from a Yarn. 

Why sheep have a thick coat of hair?

Thick coat of hair trap a lot of air. Air is a poor conductor of heat, So, hair keeps sheep warm

What are the different sources of wool?

The fleece of sheep is not the only source of wool. Angora wool is obtained from angora goats. The fur (hair) on the body of camels is also used as wool like Llama and Alpaca.

Name the some Indian bread of sheep

1. Lohi  2. Rampur bushair  3 . Nali   4. Bakharwal    5. Marwari  6. Patanwadi

Which parts of the black sheep have wool?

The hairy skin called fleece have wool in black sheep.

What is meant by the white fleece of the lamb?

White fleece means the hairy skin which is white in colour.

What is wool?

The soft, curly fibres obtained from the fleece of sheep, goat and yak etc., are known as wool.

What is selective breeding?

Certain breeds of sheep have thick coat of hair on their body which yields good quality wool in large quantities. As  these sheep are “selectively bred” with one parent being a sheep of good breed.
The process of selecting parents for obtaining special characters in their offspring is known as selective breeding.

Name the protein which is the chief component of wool fibres.

Keratin is the chief component of wool fibres

What is shearing? How it is done?

The process of removing the fleece of the sheep along with a thin layer of skin is from its body is called   shearing. It is done by using shearing machine

Which animal material is used to weave fine, soft shawls called Pashmina shawls?

The under fur of Kashmiri goat is used to weave fine, soft shawls called Pashmina shawls.

Why shearing of wool done only in summer?

Usually shearing of wool is done only in summer as sheep do not to survive without their protective coat of hair in winter.

Why wool yielding animals have a thick coat of hair?

A thick coat of hair helps in trappinga lot of air. As, air is a poor conductor of heat, it keep these animals warm.

Does shearing does hurt the sheep?

Shearing does not hurt the sheep because the uppermost layer of the skin is dead. Also, the hair of sheep grows again just as our hair does.

What is scouring?     
The sheared skin with hair is thoroughly washed in tanks to remove grease, dust and dirt. This is known as scouring.

How we get wood fibres from sheep?

The processing of fibres into wool involves the following steps:

Step I:  Shearing: - At first hair are removed using shearing machine

Step II: scouring   : - Hair is washed in tanks to remove grease, dust and dirt. This process is called scouring.

Step III: After scouring, sorting of hair is done on the basic of different textures

Step IV: The small fluffy fibres, called burrs, are picked out from the hair

Step V: The fibres then dyed in various colours, according to choice

Step VI: The coloured fibres are straightened, combed and rolled into yarn

What are the main hazards of wool industry?

Workers in wool industry get infected by a bacterium, anthrax, which causes a fatal blood disease called sorter’s disease

What is sericulture?

The rearing of silkworms for obtaining silk is called sericulture

Discuss the process of obtaining silk?

For obtaining silk, moths are reared and their cocoons are collected to get silk threads.

The cocoons are boiled to separate out silk fibres from cocoon.

Threads obtain from the cocoon spun into silk threads, which are woven into silk cloth by weavers.

The process of taking out threads from the cocoon for use as silk is called reeling the silk

Why caterpillars should not be collected with bare hands? 

Caterpillars should not be collected with bare hands because skin of caterpillars may cause allergy.

Why caterpillars need to shed their skin when they grow bigger?

The caterpillars eat their own shed skin during their growing stage and have no other food option. So they need to shed their skin when they grow bigger enter the next stage of its life history called pupa.

Why does silk have different varieties?

Silk-producing moth eats up different kinds of leaves, which accounts for the different varieties of silk. Thus, tassar silk, mooga silk, kosa silk, etc., are obtained from cocoons spun by different types of moths.

Fill in the blanks-
(i) --  China        --is the largest producer of silk.
(ii) Silk is a poor ---conductor of heat.
(iii) – Suint  ---is a dried perspiration found in raw wool.
(iv) A-- yar --is a long continuous thread.

Choose  the True statements
(a) Yarn is made of fibers
 (b) Spinning is a process of making fibers
(c) Jute is the outer covering of coconut.
(d) The process of removing seed  from cotton called ginning
(e) Weaving yarn makes a piece of fabric
 (f) Silk fiber is obtained from the stem of a plant
 (g) Polyester is a natural fiber
(h) The fleece are combed to remove Burrs
(i)  Muga is the strongest variety of Wool or Silk

(a) Yarn is made of fibers.(True)
(d) The process of removing seed  from cotton called ginning.(True)
(e) Weaving yarn makes a piece of fabric.(True)
(h) The fleece are combed to remove Burrs.(True)
(i) Muga is the strongest variety of Silk

Define: weaving, ginning, spinning

The process of arranging two sets of yarns together to make a fabric is called weaving.
The process of making yarn from fibres is called spinning
Cotton fibres are separated from the seeds by combing this process is called ginning 

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