CBSE CLASS 10 CHEMISTRY CH-1 NCERT SOLUTIONS

 


Chemical Equation and Equation are one of the outstanding chapter which is one of the main basic and main chapter. Here all solutions of NCERT are served as per latest pattern. It is very important to understand language of NCERT. So, you know which type of questions will be asked in Exam or to understand Exam Pattern.

Here, Students mainly deals with Chemical Reactions and its Equations and it’s balancing equations which is mainly done . This solutions will helps you to deal with questions easily.


# CBSE CLASS 10 SCIENCE CH-1 NCERT SOLUTIONS (Chemical Reactions And Equations)


1. Why should a magnesium ribbon be cleaned before burning in air?

Sol. Magnesium ribbon reacts with oxygen present in air to form a protective and Men layer of magnesium oxide on in surface. This layer is unreactive and prevents the ribbon from burning. Hence, it needs to be cleaned with sand paper before burning in air.


2. Write the balanced equation for the following chemical reactions: Pg 6 (i) Hydrogen + Chlorine Hydrogen chloride (ii)Barium chloride + Aluminium sulphate –Barium sulphate + Aluminium chloride (iii) Sodium + Water –Sodium hydroxide + Hydrogen

Sol(i) H2 + Cl—> 2HCI (ii) 3BaCl2 + Al2(SO4 )3 –> 3BaSO4 + 2A1C13 (iii) 2Na+ 2H20 2NaOH + H


3 Write a balanced chemical equation with state symbols for the following reactions: (1) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride. (ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.

Sol(i) BaCl2(aq)+ Na2SO4 (q) BaSO4(s)1+ 2NaCI (aq) (ii) NaOH (ag) + HCI (aq)–> NaCI (aq) + H20 (/)


4 A solution of a substance ‘,is used for white washing. • (i) Name the substance ‘X’and write its formula. r • (ii) Write the reaction of the substance ‘X’ named (i) above with water.

Sol. (i) Substance x is calcium oxide or quicklime. Is formula is Ca0 (ii) In, Quicklime reacts with water as: CaO (s)+ H20 (/) –> Ca(OH)2 (ag)


5. Why is the amount of gas collected in one of the test tubes in activity 1.7 (electrolysis of water) double of the amount collected in the other? Name this gas.

Sol. The composition of water, i.e. the chemical formula H2O, suggests that the molar ratio of hydrogen and oxygen is 2 : 1. Therefore, when water is electrically decomposed, the constituent gases hydrogen and oxygen arc produced in the same molar ratio, 2 : 1. Thus, the amount (volume) of hydrogen gas is double than that of oxygen gas. So, this gas is hydrogen

.

6. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

Sol. The colour of copper sulphate solution changes when an iron nail is dipped in it because iron being more reactive than copper, displaces copper metal from aqueous copper sulphate solution. Thus, blue colour of copper sulphate fades away to give green colour solution of ferrous sulphate. —-> Fe (s) + CuSO4(aq)  FeSO (aq) + Cu (s) – Grey Blue Green Brown


7.Give an example of a double displacement reaction other than the reaction of barium chloride with sodium sulphate.

Sol. The following reaction is a double displacement reaction 2NaOH (aq) + H2SO4 → Na2SO4 + 2H2O(L) sodium Sulphuric Sodium Water hydroxide acid Sulphate


8 Identify the substances that are oxidised and the substances that are reduced in the following reactions. (I)4Na (s)+ 02 (g)—, 2Na20 (s) (II) CuO (s)+ H2 (g) –, Cu (s)+ H2O (l)

Sol. (i) 4Na (s)+ 02 CO 2Na2O (s) Na has gained oxygen and forms Nap. So, Na is oxidised and 02 is reduced (ii) CuO(s)+H2 (g)—> Cu (s) + H20 (I) CuO has lost oxygen and forms Cu. So, Cu is reduced while H, has gained oxygen, hence, it is oxidised.


EXERCISE

1. Which of the statements about the reaction below are incorrect? 2PbO(s) + C(s) —> 2Pb(s) + CO2(g) (i) Lead is getting reduced (ii) Carbon is getting oxsidised (iii) Carbon is getting oxidised (iv) Lead oxide is getting reduced

Sol. The given reaction can be written in the form of two separate reactions: 2Pb (s) –> 2Pb C(s) –> CO2(g) Therefore, (i) and (ii) arc incorrect, while (iii) and (iv) arc correct statements.


2. Fe2O3(s) +2AI(s) –> AI2O3 + 2Fe The above reaction is an example of a (i) combination reaction (ii) double displacement reaction (iii) decomposition reaction (iv) displacement reaction

Sol. (iv) In the above reaction. Al is more reactive than Fe. So, it displaces Fe from Fe203 to form Al203. Hence, it is a displacement reaction.


3. What happens when dilute hydrochloric acid is added to iron filings? Tick the correct answer. (i) Hydrogen gas and iron chloride are produced (ii) Chlorine gas and iron hydroxide are produced (iii) No reaction takes place (iv) Iron salt and water are produced

Sol. Iron being more reactive than hydrogen. displaces hydrogen from the dilute hydrochloric acid- Thus, hydrogen gas and iron chloride a salt of iron arc formed. Fe(s)+ 2HCL (aq) –> FeCl2(aq)+ H2(q)


4. What is a Balanced chemical equation? Why should chemical equations be balanced?

Sol. A chemical change is represented by a chemical equation- When the number of atoms of different elements on reactant and product side are equal, then the chemical equation is called a balanced chemical equation. It is important to balance a chemical equation because (i) to validate the law of conservation of mass which SUMS that the mass of sealants should be equal to the mass of the products. The total mass era system is thus conserved. This law holds true only if number of atoms of reactants reacting together is equal to number of product atoms formed.
(ii) a balanced chemical equation tells us about the physical state of the reactants and products whether they arc solid (r), liquid (/) or gas (g) or aqueous (aq). (iii) it tells us about heat changes char can take place in a chemical reaction. A is the symbol of heat. Hence, it is endothermic or exothermic can he deduced from a balanced chemical equations


5 Translate the following statements Into chemical equations and then balance them: (i) Hydrogen gas combines with nitrogen to form ammonia. (ii) Hydrogen sulphide gas burns in air to give water and sulphur dioxide. (iii) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate. (iv) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Sol. 3H2 (g)+ N2 (g) —> 2Ni i3 (g) (ii) 2H2S (g)+ 302 (g) —> 2H20(1)+ 2502 (g) (ii:) 3BaCl2 (aq) + Al2(SO4)3 (aq) –> 2AlCl3 (4q)+ 3BaSO4 (s) (iv) 2K (s)+ 2H20 (l) —> 2KOH (aq)+ H2(g)


6 Balance the following chemical equations: (i) HNO3+ Ca(OH)—> Ca(NO3)2 +H2O (ii) 10Na0H+ H2SO4 —> Na2SO4 + H2O (iii) NaCI + AgNO3 —> AgCI+ NaNO3 (iv) BaCl2 + H2S04 —>BaSO + HCI

Sol. (i) 2HNO3+ Ca(OH)2 —> Ca(NO3)2 + 2H2O (ii) 2NaOH + H2SO4 —> Na2SO4 + 2H2O (iii) Nacl +AgNO3 —> AgCl + NaNO3 (iv) BaCL2 + H2SO4 —> BaSO4 + 2HCL


7 Write the balanced chemical equations for the following reactions: (i) Calcium hydroxide + Carbon dioxide Calcium carbonate + Water (II) Zinc + Silver nitrate s Zinc nitrate Silver (iir) Aluminium Copper chloride • Aluminium chloride + Copper (iv) Barium chlorides Potassium sulphate —• Barium sulphate Potassium chloride

Sol. Ca(OH)2+ CO2 —> CaCO3 + H2O (ii) Zn+ 2AgNO3 —> Zn(NO3)2 + 2Ag (iii) 2Al + 3CuCl2 —> 2AICl3 + 3Cu (iv) BaSO4 + K2SO4 —> BaSO+ 2KCI


8 Write the balanced chemical equation for the following and identify the type of reaction in each case: (i) Potassium bromide (oq Barium ) – Potassium iodide (aq) Barium bromide (s) (u) Zinc carbonate rs) Zinc oxide (s Carbon dioxide rg) rill) Hydrogen (g) + Chlorine 191 – Hydrogen chloride (g) (iv) Magnesium (s)+ Hydrochloric acid (au

Sol. 2KBr (aq) + Bal2(aq) —> 2KI (aq) + BaBr2 Type – Double displacement reaction (ii) ZnCO3 —> ZnO (s)+ CO2(g)


9. What does one mean by exothermic and endothermic reactions?

Sol. Exothermic Reactions are those reaction where there is release of Energy. Endothermic Reactions are those reaction where there is absorptions of energy.


10. Why is respiration considered an exothermic reaction? Explain.

Sol. The food taken by living beings is ultimately broken down to to glucose by the digestive system. The Glucose so formed is slowly oxidised to carbon dioxide and water with the release of heat energy. Thus, respiration is an exothermic reaction.
C6H12O6(aq) + 602(g) —> 6CO2(g) +6H2O + energy


11. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.

SOL. In a decomposition Reaction, single reactants breaks down to produce two or more products, whereas in a combination reaction, two or more reactants combine to give a single products. Thus, these reactions are supposed to be opposite of each other. 2H2 + O—> 2H2O 2H2O —> 2H2 + O2

 

12. Write one equation each for decomposition reaction where enery is suspended in the form of heat, light or electricity

SOL. HEAT CaCO3(s) —> CaO(s) + CO2 (g) (ii) LIGHT 2AgCL(s) —> 2Ag(s) + Cl2 (iii) ELECTRICITY 2H2O —> 2H (g) + O2(g)


13. What is the difference between Displacement and Double displacement reaction?

Sol. Chemical reaction in which ions exchange between two compounds and two new compounds are formed is called DOUBLE DISPLACEMENT REACTION.

When a more reactive atom creates a new substance by replacing or displace its less reactive atom in the order of reaction, such a reaction is called DISPLACEMENT REACTION.


14. In the refining of silver, the recovery of silver from Silver nitrate solution involved displacement by copper metal. Write down the reaction involved.

SOL. The reaction involved is 2AgNO3 + Cu(s) —> Cu(NO3)2 (aq) + 2Aq(s)


15. What do you mean by a precipitation reaction?

SOL. The reaction which is accompained by the formation of an insoluble solid mass (called precipitate) is known as precipitation reaction


16. A shiny brown coloured element X on heating in air becomes black in colour . Name the elements X and the black coloured compound formed.

Sol. Element X is copper and the black coloured compond is copper(II) oxide. 2Cu(s) + O2(g) —> 2CuO(s)


17. Why do wo apply paint on iron articles?

Sol. By applying paints on iron articles, they can be prevented from corrosion (rusting) . Paint does not allow oxygen (from air ) and water (moisture) to come in contact with the surface of iron.


18. Oil and Fat containing Food item are Flushed with nitrogen . Why?

Sol. Nitrogen is unreactive gas as a compared to oxygen. Oil and Fat present in the Food item get oxisidised and become rancid in the presence of air or oxygen, But Such reaction is prevented in the presence of air and oxygen. But such reaction is prevented in the presence of NITROGEN.

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