Science 1

1. CHEMICAL REACTIONS AND EQUATIONS 1. A student burns magnesium ribbon in the lab and observes a white powder falling on the table. What type of reaction has taken place and name the white powder? It is a chemical reaction. The white powder formed is magnesium oxide. 2. Balance the following equation 00 00 00 Fe3O4(s) + H2(g) Fe(s) + H2O(g) What does the symbol (s) and (g) denote? 00 00 00 3Fe(s) + 4H O(g) Fe O (s) + 4H (g) 2

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The symbol (s) denotes solid and (g) denotes gaseous state. 3. Complete the following equation sunlight

6CO2(aq) + 6H2O(l)

00 00 00 .............. + ..............

Chlorophyll

sunlight

6CO2(aq) + 6H2O(l)

00 00 00

C6H12O6 (aq) + 6 O2 (aq)

Chlorophyll

4. In the following reaction - name the reaction and the product. 00 00 00 CaO + H2O Ca(OH)2 The reaction is a combination reaction and the product is slaked lime. 5. What type of reaction takes place when decomposition of vegetable matter is converted into compost? The reaction is an exothermic reaction. 6. Green colour ferrous sulphate crystals on heat changes its colour. Write the equation and name the reaction. Heat

2 FeSO4

00 00 00 Fe2O3 + SO2 + SO3

The reaction is a decomposition reaction. 00 00 00 7. 2 AgBr 2Ag + Br2 Write one use of the above reaction. Decomposition reaction of silver bromide is used in black and white photography. -1-

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8. Why does an iron nail kept in blue copper sulphate solution fade away? Iron has displaced copper from copper sulphate solution, hence the solution appears faded. The reaction is displacement reaction. 9. You are given solutions of the following, complete the equation. 00 00 00 ................. Na2SO4 + BaCl2 Name the precipitate that is formed. 00 00 00 BaSO4 + 2 NaCl Na2SO4 + BaCl2 The white precipitate is Barium sulphate. 10. Complete the following redox reaction. 00 00 00 ZnO + C 00 00 00 MnO2 + HCl 00 00 00 ZnO + C Zn + CO

00 00 00 MnCl2 + 2H2O + Cl2

MnO2 + 4 HCl

11. ‘X’ is a shining brown colour substance, on heating in air becomes black in colour. Name the element ‘X’ and also name the compound formed. Element ‘X’

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Copper

Compound

:

Copper oxide

12. Name the chemical reaction of the following equation. 00 00 00 X + YZ XZ + Y Displacement reaction. 13. A packet of butter kept outside produces a stale smell and sour taste. What is the cause for this? Rancidity 14. A packet of potato chips packed one month earlier is crispy. Name the inert gas used for this process. Nitrogen 15. Balance the following : 00 00 00 (a) Ca(OH)2 + CO2 CaCO3 + H2O 00 00 00 (b) HNO3 + Ca(OH)2 Ca(NO3)2 + H2O 00 00 00 (c) MgCl + AgNO Mg (NO ) + AgCl 2

(d) BaCl2 + K2SO4 (e) Zn + AgNO3

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00 00 00 BaSO4 + KCl

00 00 00 Zn(NO3)2 + Ag

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(a) The equation is already balanced. 00 00 00 Ca(NO3)2 + 2H2O (b) 2 HNO3 + Ca(OH)2 00 00 00 (c) MgCl + 2 AgNO Mg (NO ) + 2AgCl 2

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(d) BaCl2 + K2SO4

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00 00 00 BaSO4 + 2 KCl

00 00 00 (e) Zn + 2AgNO3 Zn(NO3)2 + 2Ag 16. Write balanced chemical equation

(a) Hydrogen sulphide burns in air to give sulphur dioxide and water. (b) Sodium hydroxide reacts with sulphuric acid to give sodium sulphate and water. (c) Aluminium reacts with copper chloride to give aluminium chloride and copper. 00 00 00 (a) 2H2 S + 3 O2 2 SO2 + 2 H2O 00 00 00 (b) 2 NaOH + H2SO4 Na2SO4 + 2 H2O 00 00 00 2AlCl3 + 3 Cu (c) 2 Al + 3 CuCl2

17. Name the type of reaction : 00 00 00 (a) 2H2 + O2 2H2O 00 00 00 (b) Mg + CuSO4 MgSO4 + Cu 00 00 00 (c) BaCl + Na SO BaSO + 2 NaCl 2

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(a) Combination reaction (b) Displacement reaction (c) Double displacement reaction. 18. What is slaking of lime? Calcium oxide (lime) combines with water to form slaked lime. 00 00 00 CaO + H2O Ca(OH)2 Slaked lime

19. What is corrosion? The process of eating away of the metal by the action of atmospheric reagents thus changing the metal into its compounds is called corrosion. 20. Suggest a few methods to prevent Rancidity. (a) Keep the food item at low temperature. (b) Keep the food in air tight containers. 21. Write one difference between Endothermic and Exothermic reaction. Ans. Endothermic reaction Chemical reaction in which heat energy is supplied from outside.

Exothermic reaction Chemical reaction in which heat energy is given out.

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22. Why should magnesium ribbon be cleaned before burning in air ? To remove the layer of any other substance over its surface. 23. Balance the following chemical reactions. 00 00 00 Hydrogen chloride (a) Hydrogen + Chlorine 00 00 00 (b) Barium chloride + Aluminium sulphate Barium sulphate + Aluminium chloride 00 00 00 Sodium hydroxide + Hydrogen (c) Sodium + Water 00 00 00 Ans. (a) H2 + Cl2 2HCl 00 00 00 (b) 3 BaCl2 + Al2(SO4)3 3BaSO4 + 2 AlCl3 00 00 00 (c) 2 Na + 2H2O 2 NaOH + H2 24. A solution of a substance ‘X’ is used for white washing. (a) Name the substance ‘X’ named. (b) What happens when the substance ‘X’ reacts with water? (a) The substance ‘X’ is quick lime, CaO 00 00 00 (b) CaO + H2 O Ca(OH)2 Calcium hydroxide.

25. Why does the colour of copper sulphate solution change when an iron nail is dipped in it? Iron is more active element than copper. Iron displaces copper from its compound copper sulphate and changes to iron sulphate which is white in colour. 26. Identify the substance oxidised and the substance reduced in the following : 00 00 00 (i) 2Na + O 2Na O 2

(ii) CuO + H2

2

00 00 00 Cu + H2O

Substance Oxidised (i) (ii)

Na H2

Substance Reduced O2 CuO

27. Why do gold and silver not corrode in moist air? Gold and silver do not corrode in moist air because they do not react with water and oxygen of moist air. 28. In the refining of silver from silver nitrate solution involved displacement of copper metal. Write down the reaction. 00 00 00 2 AgNO3 + Cu Cu(NO3)2 + 2 Ag (c) Tiger Books Pvt. Ltd., Chennai

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29. Why do we apply paint on iron articles? Applying paint covers the metal that it does not come in contact with oxygen in air which forms rusting. 30. What happens when magnesium ribbon burns in air? When magnesium burns in air it forms magnesium oxide. 31. Name the gas evolved when zinc reacts with dil. HCl. Hydrogen gas is evolved. 32. What is an aqeous state? Solution of a substance with water as a solvent is called aqueous state. 33. Name the reaction that takes place in digestion of food. Decomposition reaction. 34. When CO2 is passed through lime water it turns milky. Why ? Lime water combines with CO2 to form a suspension of calcium carbonate which makes lime water milky. 35. A zinc rod is left for 20 minutes in copper sulphate solution. What change would you observe in the zinc rod? Zinc rod will change into zinc sulphate. 36. What is rust ? Rust is mainly hydrated iron(III)oxide. 37. A layer of oil is used on tools rather than paint. Why? Oil prevents the surface of the metal to come in contact in air while paint can be chipped out easily. 38. How does food become rancid? Food becomes rancid when fat and oil present in the food are oxidised. 39. Why are antioxidants added to fatty foods? Antioxidants are added to fatty foods to prevent their oxidation. ________ (c) Tiger Books Pvt. Ltd., Chennai