Physical and Chemical Changes - Class 7 - Science
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Extra Questions - Physical and Chemical Changes | Lakhmir Singh | Science | Class 7
In a chemical reaction, the __________ undergo chemical changes to form new __________.
A. Products
B. Catalysts
C. Reactants
D. Acids
The correct options are C. Reactants and A. Products. In a chemical reaction, the reactants undergo chemical changes to form new products. The presence of a catalyst alters the speed of the reaction but does not itself undergo any permanent chemical change.
Evaporation is a phenomenon that occurs:
A) only at boiling point
B) below boiling point
C) only above boiling point
D) at melting point"
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Sign up now"What makes litmus paper change its color?"
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Sign up nowCurdling of milk is a chemical change.
A) True
B) False
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Sign up nowVery Short Answers - Physical and Chemical Changes | Lakhmir Singh | Science | Class 7
Name the metal which is used for galvanising iron.
The metal which is used for galvanizing iron is Zinc.
Name the susbtances which are mixed (alloyed) with iron to make stainless steel.
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Sign up nowFill in the following blanks with suitable words :
(a) Changes in which new substances are formed are called __________ changes.
(b) Melting of wax is a __________change but burning of wax is a __________change.
(c) Souring of milk is a __________ change.
(d) The chemical name of baking soda is__________.
(e) When carbon dioxide is passed through lime water, it turns milky due to the formation of __________.
(f) The two methods by which rusting of iron can be prevented are __________ and __________.
(g) The process of depositing a thin layer of zinc on iron objects is called __________.
(h) The presence of __________ in sea water makes the process of rust formation on ships faster.
(i) Some susbtances can be obtained in pure state from their solutions by__________.
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Sign up nowShort Questions - Physical and Chemical Changes | Lakhmir Singh | Science | Class 7
Why is an iron grill painted frequently?
Iron grills are painted frequently to prevent them from rusting. The paint forms a protective coating that isolates the iron from environmental moisture and oxygen, which are necessary for rust formation. Regular painting helps to maintain this protective barrier and keeps the iron grills durable and aesthetically pleasing over time.
Explain why, iron pipes for carrying water are coated with zinc.
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Sign up nowWrite a word equation to represent the process of rusting of iron. Also write the chemical symbols and formulae of all the substances involved.
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Sign up nowMCQ - Physical and Chemical Changes | Lakhmir Singh | Science | Class 7
Which one of the following is not a chemical change?
(a) formation of curd
(b) ripening of banana
(c) sublimation of naphthalene
(d) corrosion of photo frame
The process of sublimation of naphthalene is not a chemical change, it is a physical change. During the sublimation process, naphthalene changes its state from solid directly to gas without going through a liquid phase, but its chemical structure does not change.
So, the correct option is: (c) sublimation of naphthalene
Which of the following are physical changes?
A. Melting of iron metal
B. Rusting of iron metal
C. Burning of iron filings
D. Drawing a wire of iron metal
(a) $\mathrm{A}$ and $\mathrm{B}$
(b) B and C
(c) A and D
(d) B and D
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Sign up nowThe gas which turns lime water milky is :
(a) sulphur dioxide
(b) nitrogen dioxide
(c) hydrogen chloride
(d) carbon dioxide
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Sign up nowLong Questions - Physical and Chemical Changes | Lakhmir Singh | Science | Class 7
What is a (a) physical change, and (b) chemical change? Give two examples of physical changes and two examples of chemical changes.
(a) Physical Change: A physical change is a temporary alteration where no new substances are formed. The change primarily affects a substance's physical properties, such as its shape, size, and state. Examples: Melting of ice into water and boiling of water to form steam.
(b) Chemical Change: A chemical change results in the formation of one or more new substances with different chemical properties. This type of change is permanent and often involves energy changes. Examples: Rusting of iron where iron oxidizes to form iron oxide, and burning of paper which produces ash, carbon dioxide, and water vapor.
What is meant by the rusting of iron? State two conditions necessary for the rusting of iron to occur. Explain how rusting damages iron objects.
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Sign up nowWhat happens when magnesium oxide is dissolved in water? Write a word equation for this process. Name the type of change which takes place.
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Sign up nowHOTS - Physical and Chemical Changes | Lakhmir Singh | Science | Class 7
When magnesium is burned in air, a powdery ash $\mathrm{X}$ is formed. $\mathrm{X}$ on dissolving in water forms $\mathrm{Y}$.
(a) What are (i) $\mathrm{X}$, and (ii) Y?
(b) What is the action of $\mathrm{Y}$ on litmus paper?
(c) What conclusion do you get about the nature of $Y$ from its action on litmus paper ?
(d) What is the common name of the indigestion-relieving medicine which contains $\mathrm{Y}$ ?
(a)
(i) X is the product of burning magnesium ribbon in the air. This powdery ash is magnesium oxide (MgO).
(ii) Y is the substance formed when X (magnesium oxide) dissolves in water. This substance is magnesium hydroxide (Mg(OH)2).
(b) Y, magnesium hydroxide, turns red litmus paper to blue, indicating its basic nature.
(c) Since Y turns red litmus paper blue, it indicates that Y is basic in nature.
(d) The indigestion-relieving medicine that contains Y, magnesium hydroxide, is commonly known as milk of magnesia. This medication is frequently used to neutralize stomach acid and relieve indigestion or heartburn.
When a grey coloured object made of metal A is left exposed to damp air for a considerable time, it gets covered with a red-brown flaky coating by the process called B which eats up the whole object gradually. It is said that the presence of $C$ and $D$ is necessary for this process to take place. If this object is galvanised by metal $\mathrm{E}$, then the process $\mathrm{B}$ does not occur.
(a) Name the metal A of which the object is made.
(b) Name the process B.
(c) What are (i) C, and (ii) D ?
(d) Name the metal E.
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