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WORKSHEET ON CHEMICAL REACTIONS Numerical Problems 1. What type of reactions are represented by the following general equations: a) A + B AB b) AL + X AX + L c) n(X) (X)n d) AB + CD AD + CB e) C A + B 2. What type of reactions are represented by the following reactions? a) CaCO3 CaO + CO2 b) NH3 + HCI NH4CI c) Zn + H2SO4 ZnSO4 + H2 d) 2H2 + O2 2H2O e) AgNO3 + NaCl AgCl(s) + NaNO3 f) 2HgO 2Hg + O2 g) NH4CNO (NH2)2CO h) Fe + CuSO4 FeS04 + Cu i) 3C2H2 C6H6 j) Cl2 + NaBr 2NaCI + Br2 k) CaO + H2O Ca(OH)2 + Heat l) Mg(OH)2 MgO + H2O m) Cu + AgNO3 Cu(N03)2 + 2Ag n) NH4NO2 N2 + 2H2O 3. Calculate the number of atoms in the following: a) 0.2 moles of nitrogen molecules. b) 3.2 g of sulphur. 4. Calculate the number of molecules in each of the following: a) 14 g of nitrogen molecules. 5. How many atoms of oxygen are present in 300g of CaCO3? [Atomic Masses: Ca = 40, C = 12, O = 16] 6. Calculate mass of the following: a) one atom of Calcium b) one molecule of SO2 (Sulphur Dioxide) 7. 6.02 x 1020 molecules of a substance weigh 44mg. What is the molecular mass of the substance? 8. The mass of a single atom of ‘X’ is 3.05 x 10-22g. Compute its Gram Atomic Mass. 9. A vessel contains 5.6g of Nitrogen (N2) gas. Calculate the following quantities: a) Number of moles of N2 b) Number of N2 Molecules c) Number of N atoms 10. Calculate the amount in each of the following: a) 6g of Carbon b) 9.9g of H2O c) 100g of Phosphorus [Atomic Mass: C = 12, H = 1, O=16, S = 32, P = 31] 11. 16HCl + 2KMnO4 2MnCl2 + 2KCl + 4H2O + 5Cl2 How many moles of Chlorine Gas will be produced from 3.2 moles of HCl? 12. Compute the mass of oxygen needed for the complete combustion of 114g of octane [C8H18]. 2C8H18 + 25O2 16CO2 + 18H2O [Atomic Masses: C = 12, H = 1, O = 16] 13. How many grams of Oxygen are required to burn 40g of sulphur? S + O2 SO2 [Atomic Masses: S = 32, O = 16] 14. Compute the mass of potassium chlorate (KClO3) that should decompose to produce 8g of oxygen. 2KClO3 2KCl + 3O2 [Atomic Masses: K = 39.1, Cl = 35.5, O = 16] 15. 0.6 moles of Cu2S is roasted in excess of oxygen to yield ‘Cu’ and ‘SO2’: Cu2S + O2 2Cu + SO2 Calculate the mass of ‘Cu’ formed. [Atomic Masses: Cu = 29, S =32] 16. 2.746g of a compound gave an analysis 1.95g of silver, 0.268g of sulphur and 0.538g of oxygen. Find the empirical formula of the compound. 17. A compound on analysis gave the following composition: Na = 32.4%, S = 22.5%, O = 45.1% The molecular mass of the compound was found to be 142. Calculate its molecular formula. [Atomic Masses: Na = 23, S = 32, O = 16] 18. A compound on analysis gave the following composition: Na = 14.31%, S = 9.97%, H = 6.22%, O = 69.5% Molecular mass of the compound is found out to be 322. Calculate its molecular formula. 19. Calculate empirical formula of Magnesium oxide from the following data: 0.2g of MgO was obtained by burning 0.12g of Mg in excess of Oxygen. [Atomic Masses: Mg = 29, O = 16] Answers to numerical problems 1. a) b) c) d) e) Combination reaction Single displacement reaction Polymerization reaction Double displacement reaction Decomposition reaction 2. a) b) c) d) e) f) g) h) i) j) k) l) m) n) Thermal decomposition reaction Combination reaction Single displacement reaction Combination reaction Double displacement reaction Decomposition reaction Isomerization reaction Single displacement reaction Polymerization reaction Single displacement reaction Exothermic reaction Endothermic reaction Single displacement reaction Decomposition reaction 3. a) 2.4092 x 1023 atoms b) 6.023 x 1023 atoms 4. a) 3.0115 x 1023 molecules 5. 5.4207 x 1024 atoms 6. a) 6.641 x 10-23 atoms b) 1.063 x 10-22 molecules 7. 44.021912 g 8. 183.7 g 9. a) 0.2 moles b) 1.2046 x 1023 molecules c) 2.4092 x 1023 atoms of N 10. a) 3.0115 x 1023 atoms b) 3.313 x 1023 molecules c) 1.943 x 1024 atoms of P 11. 1 mole 12. 400 g 13. 40 g 14. 20.433 g 15. 34.8 g 16. Ag2SO4 17. Na2SO4 18. Na2SH20O14 19. MgO Other questions Short answer-type questions 1. What distinguishes a physical change from a chemical change? 2. Which of the following are physical and which are chemical: a) Disappearance of moth balls b) Heating of iron c) Condensation of water vapour d) Rusting of iron e) Digestion of food f) Heating of iron and sulphur 3. Define the term ‘chemical reaction'. Explain it with an example. 4. What is decomposition reaction? Give one example. 5. Give one example of each: a) a single displacement reaction. b) a double displacement reaction. c) a combination reaction. d) a polymerization reaction. 6. What is a redox reaction? 7. State the electronic concept of oxidation and reduction. 8. Translate the following statements into chemical equations and balance: a) Aluminium metal replaces iron from ferric oxide (Fe2O3) giving aluminium oxide and iron. b) Phosphorous burns in oxygen to form phosphorous pentoxide. c) Carbon disulphide burns in air to give carbon dioxide and sulphur dioxide. d) Hydrogen sulphide burns in air to give water and sulphur dioxide. e) Calcium oxide reacts with water to give calcium hydroxide. f) Magnesium nitride reacts with water to give magnesium hydroxide and ammonia. g) Barium chloride reacts with sodium sulphate to give barium sulphate and sodium chloride. 9. For each of the following reactions mention which is being oxidised or reduced: a) CuO + H2O Cu + H2O b) H2 + CI2 2HCl c) SO2 + 2H2S 2H20 + 3S d) Cl2 + 2KI 2KCl + I2 e) Zn + H2SO4 ZnS04 + 4H2O f) PbS + 4H2O2 PbS04 + 4H2O g) 2NaCl + H2SO4 Na2SO4 + HCl h) CU2+ + H2 Cu + 2H+ 10. The chemical formula of ammonia is NH3. What information does this convey? 11. Define rate of reaction. Give one example each of slow and fast reactions. 12. Balance the following equations: a) NaHCO3 Na2CO3 + H2O + CO2 b) K2Cr207 + KOH H2O + K2Cr04 c) Mg + H2SO4 MgSO4 + H2 d) Ar2O3 + H2S Ar2S + H2O e) C2H6 +702 O2 + H2O f) KI + H2O2 KOH +I2 g) FeSO4 + H2SO4 + Cl2 Fe2(SO4)3 + HCl h) S + HNO3 H2SO4 + NO2 + H2O i) KMnO4 + H2SO4 K2SO4 + MnSO4 + H2O + Na2SO4 13. From the following identify the redox reactions, oxidizing and reducing agent: a) Ca(S) + Cl2(g) CaCl2 b) CuSO4 + Fe FeSO4 + Cu c) CuO + H2 Cu + H2O d) KOH + HI KI + H2O e) Zn + H2SO4 ZnSO4 + H2 f) 2Na + Cl2 NaCl g) Ca + Cl2 CaCl2 h) H2S + Cl2 2HCl + S i) Cu2+ + Zn Zn2+ + Cu