CHEMISTRY Exam questions answered. Q. 1. Explain why Al and S have diferent charges. a. Include e- arrangement for both. b. Relate the charges to the position of atoms in the periodic table. Answer:- .................Highlight to get the answers. a. Al. has the e- configuration as 2, 8. 3. S . has……………….2, 8, 6. An atom gets charged either by lending or gaining e-. Al. lends 3 e- and becomes positively charged as follows. Al - 3e- = Al 3+ (Positive ion) S atom gets charged by gaining 2 e-. ( Negative ion) S + 2e- = S2-. b. Position in the periodic table. As Al has 3 shells it is placed in the third row. As it has 3 valency e- it fits to the third column. c. Compare and contrast the reactions of Ca and Mg with water and dil HCl.
Comparison :- Both react with water and dil. acids producing hydrogen. Difference;- Calcium shows a higher rate of reaction than Mg. Q.2. a. Give two Physical properties for S and Pb. (More than two given here)
b, Explain why Zinc blocks are added to the hulls of steel ships. Answer:- Steel can easily corrode in the sea environment. Corrosion of iron or steel is an electrochemical reaction. This is due to the lending of electrons from the Iron atoms. Fe - 2e = Fe 2+ . Ferrous ions go into solution corroding the iron. These electrochemical cells need and anode, a cathode and an electrolyte. When zinc is added it becomes the anode and the hull of the ship becomes the cathode. It is the anode that oxidises. Zinc acts as a sacrificial metal as it is higher in the activity series than iron. Q. 3. a. Give the physical properties of Ammonia. Physical properties generally include  C ..........Colour. ---------------No colour. O ............Odour. -----Very strong suffocating smell. W .................Weight (Density) 0.7 kg/m3 S. ....................Solubility in water--Extremely soluble. Gas NH3 is lighter than air. Normal density of air = 1.2 kg/m3 b. Explain the reaction of blue copper sulphate crystals with Con. H2SO4 . CuSO4 .5H2O (s) = CuSO4 (s) + 5H2O The blue colour of the copper sulphate is due to the crystals. For the formation of crystals a definite proportion of water is necessary. Each CuSO4 molecule takes 5 molecules of water. ( This is known as "water of crystallization".) Concentrated sulphuric has the property of absorbing water. (Hygroscopic ) When H2SO4 is added to blue crystals they crumble to a white powder which is called "Aanhydrous copper sulphate". c. Give the Physical and chemical properties of Chlorine and ozone. Physical properties.
Chemical properties.
Resulting water
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