Class 10 Science Chapter 1 Important Questions

Class 10 Science Chapter 1 Important Questions, Extra Questions and explanation of Chemical Reaction and Equations updated for new academic session 2020-2021 based on latest NCERT Books and following the new CBSE Curriculum 2020-2021.

These questions cover NCERT Solutions of back exercises, previous year questions from CBSE Board, intext questions and extra questions for board examinations. Ask your doubts in discussion forum and get the answers by subject experts.

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Class 10 Science Chapter 1 Important Questions 2020-21

Class:10
Subject:Science
Contents:Important Questions

10th Science Chapter 1 Important Questions for Exams

Class 10 Science Chapter 1 Important Questions are given below to use online updated for new academic session 2020-2021. These sets of questions contains questions with answers of NCERT Books intext questions, back exercises questions and previous year questions. Set of important questions also contains some extra questions which are important for class tests and schools exams. These are also considered as expected questions for board exams.

10th Science Chapter 1 Important Questions Set – 1

What is meant by the Chemical Reaction?

Whenever a chemical change occurs, we can say that a chemical reaction has taken place. For example, food is cooked, milk is left at room temperature during summers, an iron tawa/pan/nail is left exposed to humid atmosphere, grapes get fermented, food is cooked, food gets digested in our body, respiration etc. Chemical change involves change in state, change in colour, evolution of a gas, change in temperature.

What do you understand by the Chemical Equation? Give example.

The description of a chemical reaction in a shorter form is called chemical equation The simplest way to do this is to write it in the form of a word-equation.
For example:
Magnesium + Oxygen → Magnesium oxide
(Reactants) (Product)
Magnesium and oxygen are reacting with each other so it is called reactants and magnesium oxide, formed during the reaction, as a product. The reactants are written on the left-hand side (LHS) with a plus sign (+) between them. Similarly, products are written on the right-hand side (RHS) with a plus sign (+) between them. The arrowhead points towards the products, and shows the direction of the reaction.

What do you mean by the Skeletal Chemical Equation?

A chemical reaction written in the form of symbols and formulae is called skeletal chemical equation. The above word-equation can be written as a balanced chemical equation:
2Mg + O2 → 2MgO
In this equation there are two oxygen atom on the LHS side while there is only one oxygen atom on the RHS side.

What do you mean by the balanced chemical equation?

A chemical reaction in which total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants. In other words, the number of atoms of each element remains the same, before and after a chemical reaction. Hence, we need to balance a skeletal chemical equation.
For example: Zn + H2SO4 → ZnSO4 + H2

What is meant by the Combination reaction? Explain with example.

The reaction in which two or more element or compound combine together to form a single compound are called Combination reaction.
Example:
(i) CaO(s) + H2O(l) → Ca(OH)2(aq) + Heat
(Quick lime) (Slaked lime)

(ii) C(s) + O2(g) → CO2(g)

(iii) 2H2(g) + O2(g) → 2H2O(l)

Types of Chemical Reactions

The different types of chemical reactions are:
Combination Reaction.
Decomposition Reaction.
Displacement Reaction.
Double Displacement Reaction.
Precipitation Reaction.
Neutralization Reaction.
Exothermic Reaction.
Endothermic Reaction.
Oxidation Reaction.
Reduction Reaction.




10th Science Chapter 1 Important Questions Set – 2

What is meant by the Decomposition reaction? Explain its other type of Decomposition reaction.

It is a type of reaction in which a single compound broke down to give two or more simpler substance.
Example:
2FeSO4(s) → Fe2O3(s) + SO2(g) + SO3(g)
(Ferrous sulphate) (Ferric oxide)
There are three different type of Chemical reaction are:
i). Thermal Decomposition: When the decomposition take place due to heat then this type of reaction is known as thermal decomposition.
Example: Ca(OH)2(aq) → CaO(s) + H2O(l)

ii). Electrical Decomposition: When the decomposition take place due to electricity then this type of reaction is known as electrical decomposition.
Example: 2H2O→2H2+O2

iii). Photolytic Decomposition: When the decomposition take place in the presence of sunlight then this type of reaction is known as photolytic decomposition.
Example: 2AgCl(s) → 2Ag(s) + Cl2

What is meant by the Displacement reaction? Give its example.

Those reactions in which a more active element displaces a less active element from its compound are called displacement reaction.
Example: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)

What do you understand by the Double Displacement reaction?

Those reactions in which two ionic compound in the solution react by exchange of their ions to form new compound are called double displacement reaction.
Example:
Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)
(Sodium (Barium (Barium (Sodium
Sulphate) chloride) sulphate) chloride)

What do you understand by the Precipitation reaction?

Those reactions in which aqua solution of two compound on mixing react to form an insoluble compound which separate out as a solid or such an insoluble compound is forms when a gas passed through the solution of compound are called precipitation reaction.
Example:
CuSO4(aq) + H2 → Cu + H2So4

What is meant by the neutralization reaction?

It is a type of reaction in which a acid react with a base to form salt and water this is known as Neutralization reaction
Example:
NaOH + HCL → NaCl + H2O

Chemical Reaction

A chemical reaction involves a chemical change in which substances react to form new substances with entirely new properties. Substances that react or take part in the reaction are known as reactants and the substances formed are known as products.

Physical Change

If a change involves change in colour or state but no new substance is formed, then it is a physical change.

Chemical Change

If a change involves formation of new substances, it is a chemical change.

10th Science Chapter 1 Important Questions Set – 3 (1 Mark)
What is meant by the Oxidation and Reduction reaction?

The gain of oxygen or loose of hydrogen is known as Oxidation reaction.
The gain of hydrogen or loosing of oxygen is known as Reduction reaction.

Differentiate between corrosion and rancidity?

Corrosion: When a metal is attacked by substance around it such as moisture, acids, etc., it is said to be corrode and this process is known as corrosion. For example, iron metal are shiny when new but with the passage of time they get coated with reddish brown powder called rust. Silver articles became black and copper articles became green on the surface due to corrosion. Corrosion cause damage to car body, bridges, iron railing, ships, etc.
Rancidity: When fats and oils are oxidized (or kept in open for some days), their smell and taste became changes. We can say that they have become rancid. This phenomenon is called rancidity. Antioxidants are adding to food containing oils and fats and oils to prevent rancidity. The antioxidant substance that are added to food are preferentially oxidized and thus they prevent the oxidation of food. Keeping food in air tight containers helps to slow down oxidation. For example: Chips manufacturer flush bags of chips with nitrogen to prevent chips from getting oxidized.

What is Decomposition reaction?

In a decomposition reaction, a single reactant decomposes to give 2 or more products. Decomposition reactions require energy in the form of heat, light or electricity
Types of decomposition reactions:
a). Decomposition reactions which require heat are known as thermolytic decomposition reactions
b). Decomposition reactions which require light are known as photolytic decomposition reactions
c). Decomposition reactions which require electricity are known as electrolytic decomposition

What are chemical equations?

Chemical equation: The symbolic representation of a chemical reaction is called a chemical equation.

Describe any three chemical reactions?

Exothermic and endothermic reactions: If heat is evolved during a reaction, then such a reaction is known as exothermic reaction. If heat is absorbed from the surroundings, then such a reaction is known as endothermic reaction
Combination reaction: Combination reaction is a reaction in which two or more substances combine to give a single product.
Decomposition reaction: In a decomposition reaction, a single reactant decomposes to give 2 or more products. Decomposition reactions require energy in the form of heat, light or electricity
8. Displacement reaction: A reaction in which a more active element displaces less active element from its salt solution.

10th Science Chapter 1 Important Questions Set – 4 (1 Mark)
State one basic difference between a Physical change and a Chemical change? [CBSE 2011]

The one basic difference is that In a Physical change no new substance is formed but in a Chemical change a new substance is formed.

What is meant by a chemical reaction? [CBSE 2011]

The reaction in which a chemical change occurs it is known as chemical reaction. A chemical reaction can be observed with the help of any of the following observations:
a) Evolution of a gas
b) Change in temperature
c) Formation of a precipitate
d) Change in colour
e) Change of state

Balance the following chemical equation: FeSo4 → Fe2O3 + SO2 + SO3 [CBSE 2008]

2FeSo4 → Fe2O3 + SO2 + SO3

Hydrogen being a highly inflammable gas and oxygen being a supporter of combustion, yet water which is a compound made up of hydrogen and oxygen is used to extinguish fire. Why? [CBSE 2011]

It is because the properties of compound (H2O) are different from the properties of its constituting elements which is H2 and O2.

State the main difference between an endothermic reaction and an exothermic reaction? [CBSE 2011]

In endothermic reaction, heat is absorbed but in the exothermic reaction, heat is evolved.

Potato chips manufacture fill the packet of chips with nitrogen gas. Why? [CBSE 2011]

Flushing bags of chips with nitrogen cuts off oxygen and protect the food from rancidity.

Write a balanced chemical equation to represent the following reaction: Carbon Monoxide react with hydrogen gas at 340 atm to from methyl alcohol. [CBSE 2011]

Co + 2H2 → CH3OH

Skeletal Chemical Equation

A chemical equation which simply represents the symbols and formulae of reactants and products taking part in the reaction is known as skeletal chemical equation for a reaction.
For example:
For the burning of Magnesium in the air, Mg + O2 → MgO is the skeletal equation.




10th Science Chapter 1 Important Questions Set – 5 (2 Marks)
If copper metal is heated over a flame it develops a coating. What is the colour and composition of coating? [CBSE 2011]

WE get a black coating of CuO, copper oxide.

N2 + 2H2 →2NH3, name the type of reaction. [CBSE 2011]

It is a combination reaction.

Which one is chemical change fermentation of fruit juice or diluting fruit juice? [CBSE 2011]

Fermentation of fruit juice is a chemical change.

Is burning of a candle wax a physical change or a chemical change? [CBSE 2011]

It is a chemical change. The hydrocarbon of wax burns to produce CO2 and H2O

What happen chemically when quicklime is added to water filled in a bucked? [CBSE 2010, 2008]

Quick lime react with water to form slaked lime and produces lot of heat and hissing sound.

CaO + H2O → Ca(OH)2 + heat + hissing sound

On what basis is a chemical equation balanced? [CBSE 2010]

It is based on the law of conservation of mass which said that mass can neither be created nor be destroy in a chemical reaction.

Name and state the law which is kept in mind when we balance a chemical equation. [CBSE 2012]

While balancing a chemical equation, we follow the law of conservation of mass which states mass can neither be created nor be destroy in a chemical reaction.

Define oxidation and reduction. [CBSE 2010, 2011]

Oxidation id addition of oxygen or removal of hydrogen. Reduction is addition of hydrogen or removal of oxygen.

Give an example of double displacement reaction. [CBSE 2010, 2011]

Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)

Balance the following chemical equation: NaOH + H2So4 → Na2So4 + H2O. [CBSE 2015]

The balanced chemical equation is

2NaOH + H2So4 → Na2So4 + 2H2O

Balanced Chemical Equation

A balanced equation is a chemical equation in which number of atoms of each element is equal on both sides of the equation i.e. number of atoms of an element on reactant side = number of atoms of that element on the product side.
As per the law of conservation of mass, the total mass of the elements present in the products of a chemical reaction is equal to the total mass of the elements present in the reactants.

10th Science Chapter 1 Important Questions Set – 6 (2 Marks)
Write balanced chemical equation for the following reaction: Silver bromide on exposure to sunlight decomposes into silver and bromine. Sodium metal react with water to form sodium hydroxide and hydrogen gas. [CBSE 2012]

(i) 2AgBr → 2Ag + Br2

(ii) 2Na + 2H2 → 2NaOH + H2

(i) What is the colour of ferrous sulphate crystals? How does this colour change after heating? (ii) Name the products formed on strongly heating ferrous sulphate crystals. What type of chemical reaction occurs in this change? [CBSE 2012]

(i) The colour of ferrous sulphate is pale green. The colour changes to reddish brown on heating due to formation of Iron (III) oxide.

(ii) 2FeSo4 → Fe2O3 + SO2 + SO3

Using balanced chemical equation explain the difference between a displacement reaction and a double displacement reaction. [CBSE 2012, 2011]

In a displacement reaction, more reactive can displace the less reactive metal from its salt solution e.g.
Cu + 2AgNo3 → Cu(NO3)2 + 2Ag

In double displacement reactions ,two compound exchange their ions to form two new compounds e.g.
NaOH + HCL → NaCl + H2O

Using a suitable chemical equation justify that some chemical reactions are determined by: (i) change in colour, (ii) change in temperature. [CBSE 2011]

(i)
Pb(NO3)2 + 2Kl → 2Pbl2 + 2KNO3

(ii)
CaO + H2O → Ca(OH)2 + heat.

Give an example each for thermal decomposition and photochemical decomposition reactions. Write relevant balanced chemical equation also. [CBSE 2012]

Thermal decomposition reaction:
Ca(OH)2(aq) → CaO(s) + H2O(l)

Photochemical decomposition:
2AgCl(s) → 2Ag(s) + Cl2

(a) A solution of substance ‘X’ Is used for white washing. What is the substance ‘X’? State the chemical reaction of ‘X’ with water. (b) Why does the colour of copper sulphate solution change when an iron nail is dipped in it? [CBSE 2011]

(a) ‘X’ is calcium oxide (CaO)
CaO + H2O → Ca(OH)2 + Heat

(b) It is because iron displaces copper from CuSo4 to form FeSo4 Which is pale green
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)

Oxidation and Reduction

Oxidation is a chemical process in which a substance gains oxygen or loses hydrogen whereas Reduction is a chemical process in which a substance gains hydrogen or loses oxygen. During a chemical reaction, there is a breaking of bonds between atoms of the reacting molecules to give products.



10th Science Chapter 1 Important Questions Set – 7 (2 Marks)

Define combination reaction. Give one example of a combination reaction which is also exothermic. [CBSE 2011]

A reaction in which two elements or compounds combine to form a single compound is called combination reaction.
CaO + H2O → Ca(OH)2 + Heat

It is also an exothermic reaction because heat is evolved.

What happens when an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride? State the physical conditions of reactants in which the reaction between them will not take place. Write the balanced chemical equation for the reaction and name the type of reaction. [Delhi 2010]

White precipitate of barium sulphate is formed. If both reactants are in solid state, then the reaction will not take place between them.
BaCl2(aq) + Na2So4 → BaSo4 + 2NaCl

It is double displacement as well as precipitation reaction.

What is redox reaction? When a magnesium ribbon burns in air with a dazzling flame and forms a white ash , is magnesium oxidized or reduced ? Why? [Delhi 2010]

The reaction in which oxidation (loss of electrons) and reduction (gain of electrons) take place simultaneously are called redox reaction.

2Mg + O2 → 2MgO

Magnesium is getting oxidised because it is losing electrons to form Mg+2 and oxygen is gaining electrons to form O-2 therefore it is getting reduced.

Write any two observations in an activity which may suggest that a chemical reaction has taken place. Give an example in support of your answer. [CBSE 2010]

Any two of these observations will suggest chemical reaction has taken place
(i) Change in state
(ii) Change in colour
(iii) Evolution of gas
(iv) Change in temperature

e.g. lead nitrate is white crystalline solid, on heating gives yellowish brown solid (lead monoxide), brown gas is evolved and a colourless gas is evolved . It shows chemical reaction has taken place.

2Pb(NO3)2(s) → 2PbO(s) + 4NO3(g) + O2(g)

When the powder of a common metal is heated in an open china dish, its colour turns black. However, when hydrogen is passed over the hot black substance so formed, it regains its original colour. Based on the above information answer the following questions: (i) What type of chemical reaction take place in each of the two given steps? (ii) Name the metal initially taken in the powder form. Write balanced chemical equations for both reactions. [CBSE 2010]

(i) In the first step, oxidation is taking place.
In second step, redox reaction take place.

(ii) Metal in the powder form is copper
2Cu + O2→ 2CuO
CuO +H2 → Cu+H2O

What is oxidation reaction? Give an example of oxidation reaction. Is oxidation an exothermic or an endothermic reaction? [Delhi 2009]

The reaction in which oxygen or electronegative element is added, Hydrogen or electropositive element is removed or loss of electrons takes place is called oxidation reaction.

Fe+2 → Fe+3 + e- (loss of electron )
C + O2 → Co2 + Heat

Oxidation reaction are mostly exothermic in nature because heat is evolved in this process.

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