CHEMICAL REACTIONS AND EQUATIONS – 2020 Important Questions

1 MARK QUESTIONS 

Q1.  In the reaction,

Be2C + xH2O  → yBe(OH)2 +CH4

write the values of x and y.

Q2.  Name the brown coloured gas evolved when lead nitrate crystals are heated in a dry test tube.

Q3. What is the difference between the following two reactions?

(i)  Mg + 2HC1 → MgCl2  + H2

(ii)   NaOH + HCl → NaCl + H2O

Q4. Double displacement reactions are also known as precipitation reactions. Why?

Q5. State one basic difference between a physical change and a chemical change.

Q6. Why is hydrogen peroxide kept in coloured bottles?

Q7.  Zinc liberates hydrogen gas when reacts with dilute Hydrochloric Acid, whereas copper does not. Write the reason?

Q8. Aluminium is a reactive metal. But is still used for packing food articles. Write one reason for its use?

Directions (Q. Nos.  09-13)  In the following questions a statement of Assertion is followed by a statement of Reason. Mark the correct choice as

(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.

(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

(c) If Assertion is true but Reason is false.

(d) If Reason is true but Assertion ls false.

(e) If both Assertion and Reason are false.

Q9. Assertion:   Chemical reaction changes the physical and chemical state of  a substance.

         Reason:  When electric current is passed through water (liquid),  it decomposes to produce hydrogen and oxygen gases.

Q10. Assertion: In a balanced chemical equation, total mass of the each element towards reactant side= total mass of the same element towards product side.

            Reason: Mass can neither be created nor destroyed during a chemical change.

Q11. Assertion: When calcium carbonate is heated, it decomposes to give calcium oxide and carbon dioxide.

            Reason: The decomposition reaction takes place on application of heat, therefore, its and endothermic reaction.

Q12. Assertion: Chips manufacturers usually flush bags of chips with gas such as nitrogen to prevent the chips from getting oxidised.

            Reason: This increase the taste of the chips and helps in their digestion.

Q13. Assertion: Rusting of iron metal is the most common form of corrosion.

           Reason: The effect of rusting of iron can be reversed if they are left open in sunlight.

Q14. Name and state the law which is kept in mind while we balance a chemical equation.

(a) Law of Equal Proportion                          

(b) Law of Conservation of Mass

(c) Daltons Law                                                 

(d) Avogadro’s Law

Q15. What is breaking and making of bonds in chemical reaction called?

(a) Chemical Reaction                     

(b) Chemical Equation

(c) Chemical Bonding                     

(d) Chemical Equilibrium

Q16. A red-brown gas is released along with O2 and lead oxide on heating lead nitrate. It is an example of

(a) combination  reaction                 

(b) oxidation reaction

(c) decomposition reaction              

(d) reduction reaction

Q17. What are the coefficients of the correctly balanced equation?

?Fe2O3 + ?CO → ?Fe+ ?CO2

(a)0, 2, 2,3           

(b) 1,3,2,3           

(c)1,2,2,2            

(d)2,6, 4,3

Q18· Burning of a candle is a

(a) physical change           

(b) a chemical change

(c) slow change                 

(d) gaseous change

3 MARK QUESTIONS

Q1. State one example each along-with the chemical equation characterised by the  following:

(i)  Change in state  

(ii) Evolution of gas

(iii) Change in temperature             

Q2. Balance the following chemical equations along with the symbols of physical states of all the reactants and the products:-

(i) Pb3O4 +HNO3 → Pb(NO3)2 + PbO2 +H2O

(ii)  C2H5OH + O2 → CO2  + H2O + Heat

(iii)  Pb3O4  + HCl→ PbCl2 + Cl2 + H2O

Q3. Study the reactions given and indicate which of the following chemical reactions will occur with suitable reason for each.

(i)  Zn(s) + CuSO4 (aq) → ZnSO4 (aq) + Cu(s)

(ii)  Fe(s) + ZnSO4(aq) → FeSO4 (aq) + Zn(s)

(iii)  Zn(s)  + FeSO4 (aq) → ZnSO4 (aq) + Fe(s)

Q4. What is a Redox reaction? Identify  the substances that  are  oxidised  and  the substances that  are reduced  in  the following  reactions:

(i) Fe2O3 +2Al → Al2O3 +2Fe

(ii) 2PbO+ C → 2Pb     + CO2   

Q5.  On heating blue coloured powder of Copper  (II)  Nitrate in a boiling tube,  Copper Oxide (black), Oxygen gas and a brown gas X are formed.

(i) Write a balanced chemical equation of the reaction.             ,

(ii)  Identify the brown gas X evolved.

(iii)   Identify the type of reaction.

(iv)  What could be the pH range of the aqueous solution of the gas X?

Q6.         (a) Mention the four type of information given by an equation.

               (b) State the law of conservation of mass as applicable in a chemical reaction.

Q8. Give reasons:

(i) All decomposition reactions are endothermic reactions.

(ii) Colour of Copper Sulphate solution changes when an iron nail is dipped in it.

(iii) Respiration is an exothermic reaction.

Q9. Write the chemical equation when:

(i) Dilute hydrochloric acid is added to solid Sodium Carbonate.

(ii) Quicklime is treated with Water.

(iii) Sodium chloride solution is added to Lead Nitrate solution.

Q10. 2g of ferrous sulphate crystals are heated in a boiling tube. Answer the following

(i) Write the colour of Ferrous Sulphate crystals both before heating and after heating.

(ii) Name the gases produced during heating.

(iii) Write the chemical equation for the reaction.

Q11. Identify the colour and chemical name of the substance of coating in silver, copper and iron when they are exposed to air.

Q12. Write an example  in each of the following case to support that :

(i) Corrosion of some metals is an advantage.

(ii) Corrosion of a metal is a serious problem.

Q13. Name the salts that are used in black and white photography.   Write the reactions when they are exposed to light. Define the type of chemical reaction taking place.

Q14. What information do we get from a balanced chemical equation?

Q15.  In a container, solid calcium oxide was taken and water was added slowly to it.

(a) State the two observations made in the experiment.

(b) Write the name and chemical formula of the product formed

Q16. Give reasons:

(a) Magnesium ribbon should be cleaned before burning in air.

(b) Photosynthesis is considered as an endothermic reaction.

(c) Combustion reaction is an oxidation reaction.

5 MARK QUESTION

Q1. Define rancidity. What kind of substances are used to prevent rancidity? Explain any three methods to prevent rancidity.

Q2. You are provided with two containers made up of copper and aluminium. You are also provided with solutions of dil. HCl,  dil. HNO3 and  H2O. In which of the above containers can these solutions be kept?       

Q3. Write balanced chemical equations for the following reactions:

(i) NaOH solution is heated with zinc granules.

(ii) Excess of Carbon Dioxide gas is passed through lime water.

(iii) Dilute Sulphuric Acid reacts with sodium carbonate.

(iv) Egg shells are dropped in Hydrochloric Acid.

(v) Copper (II) Oxide reacts with dilute Hydrochloric Acid.

Q4. A compound ‘X’  on heating with excess Conc. Sulphuric Acid at 443 K gives an unsaturated compound ‘Y’, ‘X’ also reacts with sodium metal to evolve a colourless gas ‘Z’. Identify ‘X’, ‘Y’ and ‘Z’. Write the equation of the chemical reaction of formation of ‘Y’ and also write the role of Sulphuric Acid in the reaction. 

Q5. Consider the Chemical equation given below and answer the questions that follow.

ZnO + C → Zn + CO

(a) Name the substance which is getting oxidised.

(b) Name the substance which is getting reduced.

(c) Name the oxidising agent.

(d) Name the reducing agent.

(e) What type of a reaction does this equation represent?

Q6. With the help of an activity, demonstrate how do we know that a chemical reaction has taken place?

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