Class X Science True-False, Fill in the Blank, Very Short Answer For Chemistry Ch-1 Chemical Reactions and Equations

1) Classify as physical or chemical change: Tearing of paper Production of biogas Butter going rancid magnetization of iron Clotting of blood

Answer: Physical change Chemical change Chemical change Physical change Chemical change

Two Marks Questions

Explain whether the following are physical or chemical changes. Give one reason for your answer.

1) Formation of curd

2) Ripening of fruit

3) Bending a glass tube by heating

4) Melting of wax

5) Formation of wine

6) Action of heat on blue vitriol is a physical as well as chemical change. Justify.

7) Is boiling of water, a chemical change? Give reason for your answer.

8) A person eats chocolate and then digests it. In doing so a physical and a chemical change takes place. Identify the changes and give reasons for your answer.

9) When we mix iron filings with sulfur and grind it, a physical change takes place. However, if we heat the mixture, a chemical change takes place. Explain why the former is said to be a physical change while the latter process is said to be a chemical change.

Answers:

1) Chemical change as lactic acid is formed

2) chemical change

3) Physical change

4) Physical change

5) Chemical change

6) When blue vitriol is heated,it loses it moisture , turns into white power. If we add water again, it again converts into blue color. So physical change Now when it is strongly heated, Copper Sulphate decomposes into Copper oxide and suphur dioxide.So it is a chemical change

7) Boiling of water is a physical change as new substance is formed and steam when cooled again get converted into water

8)When the person chews the chocolate and breaks it into smaller pieces - it is a physical change. No new substances have been formed as yet. Once acted upon by saliva and other digestive juices, the chocolate is broken down into other simpler substances, which can be absorbed by the blood. This is a chemical change.

9) Mixing iron filings with sulfur is considered to be a physical change because the mixture can be easily separated and no new substance is formed. Moreover, no energy changes occur while mixing iron and sulfur. When the mixture is heated, the two substances combine to form a new substance known as ferrous sulphide. The original substance, iron and sulfur, cannot be re-obtained by cooling the ferrous sulphide. Consequently, it is a permanent chemical change involving an energy change.

1)Chemical changes are generally accompanied by an exchange of energy. 2)A physical change is usually reversible. 3) When a magnesium ribbon burns brilliantly in air a physical change takes place. 4)Ammonium chloride dissolves in water with the absorption of heat. This is an exothermic.

Answers:

1) True 2) True 3) False Correct statement: When a magnesium ribbon burns brilliantly in air a chemical change takes place. 4) False Correct statement: Ammonium chloride dissolves in water with the absorption of heat. This is an endothermic reaction.

===== One Marks Questions

1) Identify physical or chemical changes in the following:

a) A rock rolls down a slope b) Baking of cake c) Plucking of fruit d) Burning of L.P.G e) Cutting of carrots

2) Explain whether the addition of dilute sulphuric acid to iron is a physical or chemical change.

3) Heating of iodine crystals is considered to be a physical change. Explain.

4) Burning of a candle may be considered as showing physical and chemical changes occurring simultaneously. Explain.

Answers:

1) a) Physical change b) Chemical change c) Physical change d) Chemical change e) Physical change

2) It is a chemical change as Iron react with dilute sulphuric acid to form Ferrous sulphate

3) When iodine crystals are heated, the solid changes to the vapor state i.e., it sublimes. This is identified as a physical change since

a) The vapors formed settle on the cooler parts of the test tube as solid - so the change is temporary and reversible.

b) There is no change in mass.

c) There is no energy (heat) change involved because the heat absorbed when the solid iodine changes to vapor, is given out when the vapor changes back to solid.

d) The chemical composition of the solid is same as that of the vapor.

4) When the candle burns, the heated wax melts. The melted wax re-solidifies and no new substance is formed, therefore this is a physical change. However, the wax and the wick continue to burn and produce new substances like carbon dioxide and water vapor. This burning process is a chemical change as it is a permanent change. Also, energy in the form of heat and light is evolved.

Fill in the blanks:-

1.Addition of hydrogen in a substance in a reaction is known as ____ reaction.

2.In a reaction two or more substances combine to form a new single substance.

3.Unbalanced reactions are also known as ____

4.Reactions in which heat is given out along with the products are called  ____ reactions.

5.Reactions in which energy is absorbed are known as ___ reactions.

6.When as element displaces another element from its compound, a reaction occurs. 7.Those reactions, in which two compounds react by an exchange of ions to form two new compounds, are called reactions

8.Precipitation reactions produce salts.

9.Reduction is the ____ of oxygen or gain of hydrogen.

10.The digestion of food in the body is an example of reaction.

11.The addition of oxygen to a substance is called .

12.When calcium carbonate is heated, it decomposes to give ____ and ____

Answers:

1.reduction

2.Combination

3.skeletal

4.Exothermic

5.Endothermic

6.Displacement

7.Double displacement

8.Insoluble

9.Loss

10.Decomposition reaction

11.Oxidation

12.CaO(s) and CO₂

True/ False:-

1.The number of atoms of each element is conserved in any chemical reaction.

2.Oxidation is the loss of electrons from a substance.

3.Reduction is the gain of electrons by a substance.

4.A complete chemical equation represents the reactants, products and their physical states symbolically.

5.A magnesium ribbon burns with a dazzling flame in air (oxygen) and changes into a white substance, magnesium oxide.

6.Rusting is a double decomposition reaction.

7.The reaction between nitrogen and hydrogen to give ammonia is an example of a combination reaction.

8.Action of heat on ferrous sulphate is an example of decomposition reaction.

9.The formation of Na+ and CI- ions from sodium and chlorine is an example of a redox reaction.

Answers:

1. TRUE 2. TRUE 3. TRUE 4. TRUE 5. TRUE 6. FALSE 7. TRUE 8. TRUE 9. TRUE

Question 1. Write a chemical equation when magnesium metal reacts with aqueous hydrochloric acid to produce a solution of magnesium chloride and hydrogen gas.

Question 2. Can a combination reaction be redox reaction.

Question 3. Why do we apply paint on iron articles?

Question 4. What are the different types of reactions?

Question 5. What is a decomposition rection ? Give example.

Question 6. Define displacement reaction.

Question 7. What happens when sodium reacts with water?

Question 8. Write the chemical equation and name the reaction when a solution of sodium chloride is mixed with a solution of silver nitrate and a white precipitate of silver chloride is formed.

Question 9. Why does the color of copper sulphate solution change, when an iron nail is dipped in it?

Question 10. Why is photosynthesis considered as an endothermic reaction?

Question 11. Potassium chlorate (KCIO3) on heating forms potassium chloride and oxygen. Write a balanced equation for this reaction.

Question 12. Give an example of a chemical reaction characterized the change in temperature.

Question 13. What type of chemical reactions take place when: a)Limestone is heating? b)A magnesium wire is burnt in air? c)Electricity is passed through water? d)Ammonia and hydrogen chloride are mixed? e)Silver bromide is exposed to sunlight?

Question 14. To balance a chemical equation, can we change the formula of either reactants or products?

Question 15. Why should a magnesium ribbon be cleaned before burning in air?

Question 16. If an of the following reactions occurs spontaneously, write the balanced net ionic equation. If not, write no reaction

a)Pb + Zn₂ +_ Pb₂ + + Zn

b)Fe + H+ _Fe₂ + + H₂

c)Cu + Ag+ _ Cu₂ + + Ag

d)Cr + Zn₂ + _Cr₃ + + Zn

Question 17. Nickel (II) nitrate is prepared by heating nickel metal with liquid dinitrogen tetroxide. In addition to the nitrate, gaseous nitrogen monoxide is formed. Write the balanced equation.

Question 18. Why is the amount of gas collected in one of the test tubes in electrolysis of water double of the amount collected in the other? Name this gas.

Question 19. Write a balanced chemical equation with state symbols for the following reactions:- i.Solution 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.

Answers:

1) Mg + 2HCL ? MgCl₂ + H₂

2) Yes,a combination reaction can be a redox reaction. In a combination reaction two elements are combined to make a single product. 2H₂ +O_{2 –>} 2H₂ O (water's formula) In this reaction there is reduction of oxygen as there is transfer of electrons from hydrogen to oxygen and there is also oxidation of hydrogen as there is acceptance of electrons by oxygen from hydrogen.Oxygen is the oxidizing agent and hydrogen is the reducing agent.

3) To prevent it from Corrosion 4) Combination reactions Decomposition reaction Displacement reactions Double displacement reactions Oxidation and Reduction reactions

5) Those reactions in which a compound splits up into two or more simpler substances are known as decomposition reactions.

6) Those reactions, in which one element takes the place of another element in a compound, are known as displacement reactions. CuSO₄ + Zn ? ZnSO₄ + Cu

7) Sodium can react with cold water as it is an extremely reactive metal; when it does,

2Na + H₂ O –> H₂ + Na₂ O (Sodium Oxide)

The reaction is very vigorous and exothermic.

8) NaCl + AgNO₃ ? AgCl + NaNO₃ Double displacement and precipitation reaction

9)When an iron nail dipped in the copper sulphate solution than iron displaces copper from the copper sulphate because iron is more reactive than copper. Therefore the color of the copper sulphate solution changes.

10) Photosynthesis is considered an endothermic reaction because energy in the form of sunlight is absorbed by the green plants.

11) 2KCIO₃ ? 2KCL + 3O₂

19) i) BaCl₂ + Na₂ SO₄ ? BaSO₄

ii) NaOH + HCL ? NaCl + H₂ O