CURRENT EXAMINATION: NECO Chemistry Objective & Essay; Verified Chemistry OBJ: 1-10: AEECABADCB 11-20: CEADBBDEDD 21-30: DCAAADBCAB 31-40: ECAABCABAA 41-50: AADDDCCDBB 51-60: ADCCCACDCD THEORY; (1ai).law of constant composition states that samples of pure compound always contain the same element in same mass and proportion. (1aii).diagram for separation of petrol and water. (1bi)the two characteristics each of physical and chemical change are: -physical change,no new substances is formed. -chemical change, new substances are formed. -Physical change much heat is not needed. Chemical change,much heat is needed. (1bii).physical change,seperation of mixtures by seperation while chemical change rusting of iron addition of water to quicklime. 3a) (i)electrolysis is the chemical decompostion of compound which takes place when an electric current is passed through a solution (ii)electrode: these are condcutors(poles of carbon or metal) through whichan electric current enters or leaves the electrolyte. (3b) quantity of electricity used (Q)=it =2.6*(70*60)=10920c Ag(+)+2e(-)=>Ag 1 mole of AG will deposit 2*96500c=193,000 mass = (10920*108) /193,000 =412.22g 3bii -purification of metal -extraction of metals -for industrial preparation of certain chemical 3biii Exothermic reaction is a chemical reaction in which heat is given off to the surrounding while Endothermic reaction is the one in which heat is absorb from the surrounding 3biv Amphoteric oxide is defined as oxide of metal which can behave both as basic oxides and as acidic oxide 3ci -methyl orange -phenophtalyne.
Posted on: Tue, 18 Jun 2013 16:23:24 +0000
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