7th Grade > Chemistry
PHYSICAL AND CHEMICAL CHANGES MCQs
Total Questions : 113
| Page 1 of 12 pages
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Explanation: 1 Mark
Chemical Equation: 1 Mark
The standard test of carbon dioxide is by passing it through lime water.
When carbon dioxide is passed through lime water, calcium carbonate is formed, which turns lime water milky.
Carbon dioxide (CO2) + Lime water [Ca(OH)2] → Calcium Carbonate(CaCO3) + Water (H2O)
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Explanation: 1 Mark
Name of theprocess: 1 Mark
The exposed surface of sliced applesturnbrown due to oxidation which is a chemical change.
Cuttingofapples is a physical change as no chemical reaction takes place in this process.
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Differences with examples: 5 Marks
PhysicalChemicalCompositionofthesubstancedoesnotCompositionofthesubstancechanges.change.Mostchangesarereversible.Mostchangesareirreversible.Nonewsubstancesareformed,e.g,Newsubstancesareformed,e.g,Ice→Water→SteamBurningofPaper→AshesForexample,meltingofice,dissolvingsaltinForexample,rustingofiron,decayoffoodwaterPhysicalchangesarethosechangeswhichChemicalchangesinvolvechangeinchemicalinvolvechangeinonlyphysicalpropertieslike,propertiesofthesubstancesandchangeincolor,size,shapeandstateofsubstancesetc.chemicalcompositionalso.
Answer: Option B. -> galvanization
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B
One of the simple ways to prevent rusting is toapply a coatingof paint or greaseon the surface of iron. In fact, these coats should be applied regularly to prevent rusting. Another way to prevent rusting is to deposit a layer of a metal like chromium or zinc on iron.This process of depositing a layer of zinc on iron is known as galvanization.
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B
One of the simple ways to prevent rusting is toapply a coatingof paint or greaseon the surface of iron. In fact, these coats should be applied regularly to prevent rusting. Another way to prevent rusting is to deposit a layer of a metal like chromium or zinc on iron.This process of depositing a layer of zinc on iron is known as galvanization.
Answer: Option A. -> Crystallisation
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A
The process of obtaining large crystals of pure salt from sea water is known ascrystallisation.
The process of crystallisation is used to purify a large number of water soluble solids. Common salt obtained from sea water is an impure substance having many impurities in it.
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A
The process of obtaining large crystals of pure salt from sea water is known ascrystallisation.
The process of crystallisation is used to purify a large number of water soluble solids. Common salt obtained from sea water is an impure substance having many impurities in it.
Answer: Option C. -> Burning of wood
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C
When we light the wood up, it burns gently and after a while, it turns into ashes. As it burns, it produces heat, light and smoke which escapes through the chimney. The heat, light, fire and smoke are all good characteristics of a chemical change, which result in a completely new matter i.e. ashes.In the other options like cutting of wood, melting of ice and dissolving sugar in water, no new substances are formed. So, these are examples of physical changes.
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C
When we light the wood up, it burns gently and after a while, it turns into ashes. As it burns, it produces heat, light and smoke which escapes through the chimney. The heat, light, fire and smoke are all good characteristics of a chemical change, which result in a completely new matter i.e. ashes.In the other options like cutting of wood, melting of ice and dissolving sugar in water, no new substances are formed. So, these are examples of physical changes.
Answer: Option A. -> True
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A
The change due to which the one substance is transformed into another substance having new and different chemical properties is called a chemical change.
Curdling of milk is a chemical change as a new substance (curd) is formed which has different taste, form, properties and it cannot be converted back to milk.
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A
The change due to which the one substance is transformed into another substance having new and different chemical properties is called a chemical change.
Curdling of milk is a chemical change as a new substance (curd) is formed which has different taste, form, properties and it cannot be converted back to milk.
Answer: Option B. -> Content of moisture in air is high in rainy season whereas air is almost dry in summer season.
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B
Content of moisture in air is high in rainy season whereas air is almost dry in summerseason. For rusting, the presence of both oxygen and water is essential. Rusting becomes faster, if the content of moisture in air is high. Hence, rusting of iron objects is faster in rainy seasonthan in summerseason.
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B
Content of moisture in air is high in rainy season whereas air is almost dry in summerseason. For rusting, the presence of both oxygen and water is essential. Rusting becomes faster, if the content of moisture in air is high. Hence, rusting of iron objects is faster in rainy seasonthan in summerseason.
Answer: Option C. -> physical change as only the shape of the axe changes
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C
A blacksmith grinds the edges of iron axe against a spinning wheel to sharpen it. Sparks of fire and heat are generated due to the friction between the objects. So,we can say that it is a physical change as only theshape of theaxe changes.
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C
A blacksmith grinds the edges of iron axe against a spinning wheel to sharpen it. Sparks of fire and heat are generated due to the friction between the objects. So,we can say that it is a physical change as only theshape of theaxe changes.
Answer: Option B. -> Magnesium hydroxide is formed
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B
When magnesium oxide is dissolved in water, magnesium hydroxide is formed. So, the reaction between magnesium oxide and water is a chemical change,as a new substance(magnesium hydroxide) is formed.
MgO+H2O→Mg(OH)2
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B
When magnesium oxide is dissolved in water, magnesium hydroxide is formed. So, the reaction between magnesium oxide and water is a chemical change,as a new substance(magnesium hydroxide) is formed.
MgO+H2O→Mg(OH)2
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