7 April 2013

chemistry practical

CHEMISTRY PRACTICALS 2013 1. VOLUMENTRIC ANALYSIS QUESTION 1. 'A' is a solution of tetraoxosulphate(vi). B is a solution coomtaining !.4g of potassiumb hydroxide per 25.0cm3. (a.) Put A into burette and titrate with 20.0cm3 or 25.0cm3 portion into of B using Methyl Orange as an indicator. Record the volume of your pipette. Tabulate your burette readings and calculate the average volume of acid used. (b.) From your result and information provided. Calculate the (i.) Concentration of B in mol/dm3 (ii.) Concentration of A in mol/dm3 (iii.) Number of Hydrogen ions in 1.0dm^2 of A. The equation for the reaction is: H2SO4 + 2KOH --> k2SO4 + 2H2O. {H=1, O=16, K=39} SOLUTION Burrete reading(cm3)| Rough | 1st | 2nd| 3rd Final(cm3) | 18.60 | 18.00| 20.30| 28.00 Initial(cm3) | 0.00 | 0.00 | 2.30 | 10.00 Vol. Acid used(cm3)| 18.60 |18.00 | 18.00| 18.00 The average volume of acid used = 18.00+ 18.00 + 18.00/3 = 18.00cm3. (bi.) Mass of KOH per dm3 of B = 39+16+1= 56. Conc. of B = 5.6/56 = 0.01mol/dm3. (bii.) The equation for the reaction is: H2SO4 + 2KOH --> k2SO4 + 2H2O. From the equation ==> Conc of A * Volume of A * Mole ratio = CA*18.00/0.10*2 = 1/2 .'. CA= 0.10 * 25/2*18' CA= 0.0694mol/dm3. (biii.) 1dm3 of 1.0mol/dm3 H2SO4 contains (2*6.0*10^23). Hydrogen atom ==> 1dm3 of 0.694mol/dm3 H2SO4 contains 2*6.0*10^23 = 8.328x10^22. ------------------------------------------------ NOTE: THIS IS JUST A STUDY OF THE SPECIMEN THAT WAEC PROVIDED. THESE ARE LIKELY QUESTION U WILL SEE ON PRACTICAL DAY. TRY TO USE THE END POINT( ie Ur school's Volume of acid used) OF UR SCHOOL( IT MATTERS A LOT); AS OURS IS 18.00 AS SHOWN ABOVE.. ***SUBSRIBERS SHOULD NOT WORRY COS THEY WILL GET THE EXACT ANSWERS ON THE EXAM DAY AS THEY PAID FOR.. SUBSCRIBE NOW! ---------------------------------------- QUESTIONS & SOLUTIONS to QUANTITATIVE/ SALT ANALYSIS: -QUESTION (2a.) C & D are inorganic salts. X is a solution of an inorganic compound. Carryout the following exercises on C, D& X. Record your observations and identify any gas (es) evolved. State the conclusion drawn from the result of each test. [i.] Add about 5cm3 of distilled water to sample C in a test tube and shake thoroughly. Divide the esulting solution into two portions. [ii.] Put about 2cm3 of X into seperate test tubes and add the first portion of solution in (2ai). [iii.] To the second portion of the resulting solution in (2ai), add few drops of BaCl2(aq) followed by excess dil HCl. [bi.] To about 2cm3 portion of the resulting solution in a test-tube, add NaOH in drops and in excess. [ii.] To another portion of the resulting solution, add few drops of dilute trioxonitrate. SOLUTION TEST [2ai.] C + distilled H2O. [ii.] 1st portion + BaCl2(aq). [iii.] 1st portion + BaCl2 + HCl. [iv.] Residue + dil HCl. [bi.] 2nd portion + NaOH in drops + excess NaOH. [ii.] C + HNO3. [iii.] C + dil HNO3 + NH3 in drop and in excess NH3. OBSERVATIONS [2ai.] Dissolves completely. [ii.] White ppt is formed. [iii.] Ppt dissolved. [iv.] A colourless gas is elvolved and effervescence occured. [bi]. Dark green ppt. Ppt insoluble in excess NaOH. [ii.] Effervescence occured. [iii.] Insoluble in drop. Soluble in excess NH3. INFERENCE [2ai.] A soluble salt is present. [ii.] SO4^2-, SO3^2-, S^2-, or CO3^2- suspected. [iii.] SO3^2- present. [iv.] H2 present. [bi.] Fe^2+ Confirmed. Fe^3+ formed. [ii.] CO2- suspected. [iii.] SO3^2- present. NOTE THAT ^ Means Raise to Power and above is a questi0n likely to show up during the exam. Use it and refresh ur memory.... PLS THIS IS NOT THE EXACT QUESTION YOUWILL SEE THAT DAY....

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