On this Page we have given West Bengal Class 8 English Medium Science Solution Chapter 2.3 Chemical Reactions Question and Answer for our Students of West bengal Class 8 English Medium. Hope this following Question Answer will help our Students.
West Bengal Class 8 | Science | Chemical Reactions
MCQ
1 ) ______ are the chemicals which take part in a chemical reactions
a ) by-products b) reactants c) ingredients d) constituents
Ans. Reactants
2) Burning will not be possible without the presence of _____ gas
a ) oxygen b) nitrogen c) helium d) hydrogen
Ans. Oxygen
3) Out of the few factors of chemical reactions , which one is required for the process of photosynthesis
a ) pressure b) temperature c) light d) wind
Ans. Light
4) The reason why no bubble is evolved when dry baking soda and tartaric acid is mixed with kerosene is
a ) baking soda is a ionic compound
b ) kerosene can’t dissolve ionic compound
c ) H+ ions are not produced in the process
d ) all of them
Ans. All of them
5) We can use ______ to decompose an aqueous solution with little sulfuric acid
a ) electricity b) vibrations c) pressure d) heat
Ans. Electricity
6) ____ are often added during chemical reactions to speed up the process
a ) coagulants b ) alum c) catalyst d) booster
Ans. Catalyst
7) Which of the statements is incorrect about catalyst
a ) there is just a single catalyst
b) they are regenerated after the process
c) they are always found by experiment
d) both b and c
Ans. There is just a single catalyst
8) It is advised to use powdered MnO2 instead of big chunks of MnO2 because
a ) volume of MnO2 will be increased
b) surface area of MnO2 will be increased
c) mass of MnO2 will be increased
d) all of the above
Ans. Surface area of MnO2 will be increased
9) Most of the organic catalyst or enzyme are _____ in nature
a ) protein b) carbohydrate c) fat d) vitamin
Ans. Protein
10) Identify the catalyst in potato which fastens the decomposition of hydrogen peroxide
a ) lipase b) maltase c) catalase d) lactase
Ans. Catalase
11) The chemical changes that results into the evolution of heat is known as
a ) endothermic b) exothermic c) hypothermic d) thermic
Ans. Exothermic
12) Apart from one all others are examples of exothermic reactions
a ) burning of carbon
b) reaction of quicklime with water
c) combustion of methane
d) melting of ice
Ans. Melting of ice
13) Which observation should be present for a reaction to be a chemical reaction
a ) a colour change
b) evolution or absorption of heat
c) evolution of a smell
d) anyone of them
Ans. Anyone of them
14) what’s so unique at light emitted at 1000⁰C
a ) its nkot a white light
b) it contains UV radiation
c) it has shorter wavelength
d) there is slight reduction in speed
Ans. It contains UV radiation
15) The by-products during the process of combustion are
a ) Carbon monoxide and carbon dioxide
b) carbon dioxide and water
c) carbon monoxide and water
d) carbon dioxide, carbon monoxide and water
Ans. Carbon dioxide and water
16) Carbon dioxide can be easily identified if it
a ) turns lime water milky
b) there is a pungent smell
c) the person feels dizziness
d) a slight whitish gas can be seen
Ans. Turns lime water milky
17) The compound formed when metals or non metals react with oxygen during the combustion process is
a ) salts b) bases c) oxides d) alkalis
Ans. Oxides
18) It’s the reddish brown coating formed on iron after oxidation process it known as
a ) rust b) precipate c) remains d) composite
Ans. Rust
19) Which of the following glasses won’t have their nails rusted
Ans – C
20) Addition of ______ instead of oxygen in a reaction is also known as oxidation
a ) chloride b) carbon c) chlorine d) calcium
Ans. Chlorine
21) If ____ is removed from a substance they that reaction is also termed a oxidation reaction
a ) hydrogen b) helium c) nitrogen d) chlorine
Ans. Hydrogen
22) The reaction where oxygen is eliminated from the compound is known as
a ) substitution reaction
b) elimination reaction
c) alteration reaction
d) reduction reaction
Ans. Reduction reaction
23) N2 + 3H2 ->2NH3 , what type of reaction is this
a ) oxidation
b) reduction
c) galvanization
d) alteration
Ans. Reduction
24) After the occurrence of reaction the total number of electrons are
a) decreased
b) increased
c) remains same
d) Increases significantly
Ans. Remains same
25) What is an absolutely incorrect statement about reductants
a ) removes oxygen from a substance
b) removes chlorine from a substance
c) adds electrons to an atom , ion or radical
d) removes hydrogen from a substance
Ans. Removes hydrogen from a substance
Q.(2) short answer questions.
(1) Which gas is revolved on heating of hydrated cupric nitrate ?
→ Brown coloured nitrogen dioxide gas is evolved.
(2) Which thing is essential for photosynthesis to happen?
→ Light is necessary for photosynthesis.
(3) What happens when water is added to baking soda and tartaric acid mixture?
→ Bubbles evolve rapidly.
(4) Name two solvents which cannot dissolve ionic compounds?
→
- Kerosene
- Benzene
(5) Name the solvent in which ionic compounds dissolve easily?
→ Water
(6) What is catalyst?
→ Substance which is speed up the specific chemical reaction called as catalyst.
(7) Name the catalyst involved in the reaction of mixture of hydrogen peroxide with equal volumes of water ?
→ Manganese dioxide ( MnO2 )
(8) Give One property of catalyst?
→ Catalyst participated in the reaction but regenerated at the end .
(9) What are called as organic catalyst?
→ Enzymes are called as organic catalyst.
(10) What is exothermic reaction?
→ Chemical reaction that evolves heat called as exothermic reaction.
(11) Give the definition of endothermic reaction ?
→ Chemical reaction that absorbs heat called as endothermic reaction.
(12) Give example of exothermic reaction.
→
- Burning of any fuel
- Combustion of methane
(13) Give example of endothermic reaction.
→
- Making of quicklime from limestone.
- Melting of ice cubes
(14) What do you mean by the term combustion ?
→ When wood and coal are set to fire in an open air, it produces heat and light. Paraffin kerosene and cooking gas also burn in open air producing heat and light and this process is called as combustion.
(15) What happens when charcoal inserted in oxygen filled gas jar ?
→ Charcoal, being a combustible substance , Burns to produce Ash.
(16) What do you mean by the term rust ?
→When iron kept in open air, the reddish-brown coating is produced on it surface is called as rust.
(17) Define the term oxidation in terms of oxygen ?
→ Reaction in which oxygen combines with an element to form a product is called as oxidation.
(18) Define the term oxidation in terms of hydrogen ?
→Reaction in which hydrogen is eliminated from the substance to form a product is called as oxidation.
(19) Define the term reduction in terms of oxygen ?
→ The reaction in which oxygen is eliminated from the substance to form a product is called as reduction.
(20) Define the term reduction in terms of hydrogen ?
→The reaction in which hydrogen combines with an element or compound to form a product is called as reduction.
(21) The reaction in which hydrogen combines with nitrogen
To form ammonia, which substance will get reduced ?
→ Nitrogen get reduced.
(22) What do you mean by reductant?
→ The oxidized substance in the reaction which cause reduction of another substance called as reductant or reducing agent.
(23) What do you mean by oxidant ?
→The reduced substance in the reaction which cause oxidation of another substance called as oxidant or oxidizing agent.
(24) Define oxidation in terms of electrons?
→ Elimination of electron from atom, ion or radical during the reaction is called as oxidation.
(25) Define reduction in terms of electrons ?
→ Addition of electrons to an atom ion or radical during the reaction is called as reduction.
(26) Which substance will get reduced when hydrogen gas
passed over the hot, black cupric oxide ?
→The black oxide will get reduced to reddish brown metallic copper.
(27) Which substance will get oxidized when hydrogen gas passed over the hot and black cupric oxide ?
→ In above reaction, hydrogen will get oxidized to form water .
(28) What happens when zinc oxide is heated with coke ?
→ Coke gets oxidized to form carbon monoxide and zinc oxide will get reduced to zinc.
(29) What get oxidized during rust ?
→ During rusting, iron gets oxidized first into ferrous iron and further oxidation occurs to produce ferric iron.
(30) What are the two-reduction reaction occurs in rusting ?
→
- Hydrogen gas is produced or reduction of hydrogen ions in water.
- Water is formed upon reduction of oxygen.
Also See: Previous Chapter Chemical Effects of Electricity Question Answer