WAEC 2016 CHEMISTRY QUESTIONS AND ANSWERS NOW AVAILABLE FOR FREE

Monday 18th April 2016 CHEMISTRY 2 (ESSAY) 2.00PM � 4.00PM CHEMISTRY 1 (OBJ) 4.00PM � 5.00PM CHEMISTRY OBJ: 1-10: CAACABCDBC 11-20: BABAADBDCA 21-30: BCCAABCDCB 31-40: ABCBCCCBBC 41-50: ABDBBBAABB ++++++++++++++++++++++++++ (1a) Nucleons is the sum total of neutrons and protons in the nucleus of an atom. It is the molecular weight of an atom. (1b) Graham 's law of diffusion states that at a constant temperature and pressure , the rate of diffusion of a gas is inversely proportional to the square root of it density (1c) Because when aluminum is exposed to moist air, a thin continuous coating of aluminum oxide is formed , which prevents further attack of the aluminium by atmospheric oxygen and water or steam under normal conditions (1d) (i) electron affinity (ii) electronegativity (iii) ionization energy (1e) (i) the molecule of real gases occupies space and there are forces of the attraction between them (ii) real gases do liquefy when their temperature droops. (1f) (i) used in separation of different component of crude oil . (ii)it is used for separating acetonic from water (iii) it is used for obtaining different gases from air for industrial use . (1g) (i) concentration of ions in electrolyte (ii)the nature of the electrode (iii)the position of ions in the electrochemical series (1h) (i) substitution reaction (ii)addition reaction (1i) (i) carbon dioxide (ii) water vapour (iii)carbon monoxide (1j) (i) centrifugation (ii)sieving (iii)evaporation to dryness ================================== (2ai) Isotopy (2aii) They have the same atomic number but different mass number (2aiii) -Chlorine -Carbon -Oxygen (2aiv) PHYSICAL PROPERTIES -Metals are malleable while non metals are not malleable -Metals are ductile while non metals are not ductile -Metals are sonorous while non metals are not sonorous -Metals have high densities while non metals have low densities CHEMICAL PROPERTIES -Metals are reducing agent while non metals are oxidising agent -Metals form basic oxide while non metals form acidic oxide -Metals lose electron while non metals gain electrons (2bii) I-Al2O3 -ZnO II-CaH2 III-CaCO3 IV-CaCl2 -NaCl (2ci) -They have variable oxidation state -They have partially filled d-orbital -They have typical metallic properties -They have tendency to form complex ions (2cii) The d orbital is completely filled (2d) 106g of Na2CO3-84g of mgCO3 xg of Na2CO3-3.36 of mgCO3 xg=(106*3.36)/84 =356.16/84 x=4.24g ================================== (3ai) This is the existence of compounds with the same molecular formular but with different structural formular (3aii) I-Tertiary alcohol II-primary alcohol III-secondary alcohol (3bi) I-CH3CH2COOK + H2 II-CH3CH2COOC4H9 + H2O III-CH3CH2CH2COOH (3bii) I-Sodium propanoate II-Butylpropanoate III-Butanoic acid (3c) 7.0g of R = 2.24dm^3 xg of R = 22.4dm^3 x=(7.0*22.4)/2.24 =70.0g of R (3ci) TABULATE |C |H % by mass |85.7|14.3 atomic mass|12 |1 mole ratio|85.7/12|14.3/1 =7.14|14.3 Divide by smallest=7.14/7.14|14.3/7.14 =1|2 Empirical formular=C1H2=CH2 (ii)Molecular formular (CH2)n=70 (12+2)n=70 14n=70 n=70/14=5 Molecular formular=(CH2)5=C5H10 (3d) diagram ============================ (4ai) calcium chloride, CaCl2 (4aii) to the unknown substance in a gas jar, add small quantity of lime water. if the gas is carbon(iv)oxide, it turns lime water milky while carbon (ii) oxide has no effect (4bi) oxygen is releasedf abundantly from air and nitrogen is produced by the reaction of potassium trioxonitrate(v) with concentrated hydrochloric acid (4bii) oxygen gas rekindle a lighted splint while nitrogen does not (4ci) Bauxite is preferred because it is readily available in the earth crust (4cii) -trioxosilicate(iii) -carbon(iv)oxide (4ciii) -it helps to purify the bauxite (4civ) it is difficult to extract aluminium by chemical reduction of aluminium oxide in amphoteric (4cv) AL2O3+NaOH=>Na2O + Al+ H20 ===================================== (5ai ) Na2S2O3 ===> 2+2x+6=0 2x=6-2=4 X=4/2 X=2 The oxidation number of sulphur is 2 (5aii) Rhombic & monoclinic (5aiii ) -Both are tetravalent -both are allotrope of carbon (5bi) CO2 & Chloroflorocarbon (5bii) There is increase in sun radiation reaching the earths surface ie Global warming (5biii ) ThunderStorm (5iv) I 2KNo3 ----> 2KNO3 + O2 II AgNo3 ---> 2Ag + 2NO3 (5ci) Calcium chloride in a solution can give rise to crystal using filteration & evaporation to dryness . The sol is filtered into filtrate & residue b4 evaporation to dryness takes place . (5cii) - Because of presence of hydrogen bonding in NH3 -Because Iodine as higher molecular mass than chlorine (5di) Mol of Nacl = Mass/MM = 5.85/58.01 = 0.1mol From the equation 2mol of Nacl gives 2mol of HCL, 0.1mol of Nacl gives 0.1mol of Hcl Vol of Hcl = 0.1 x 22.4 = 2.24mol/dm^3 ++++++++++++++++++++++++++++ ===COMPLETED=== ++++++++++++++++++++++++++++