NECO CHEMISTRY PRACTICALS.

VOLUMETRIC ANALYSIS 1. A is 0.125mol/dm3 of H2SO4. B is a solution containing xgdm^-3 of NaOH. (a.) Put A into the burette and titrate it against 20.0cm3 or 25.0cm3 portion of B using Methyl Orange as indicator. Record the volume of your pipette. Tabulate your burette readings and Calculate the average volume of A used. THE EQUATION FOR THE REACTION IS H2SO4(aq) + 2NaOH --> Na2SO4 + 2H2O From Your result and Information provided above, Calculate (i) the amount of H2SO4 in the the average volume of A used. (ii) Concentration of B in mol/dm3 (iii) Value of X. [H=1,O=16,Na=23] SOLUTIONS The Equation for the Reaction: H2SO4(aq) + 2NaOH --> Na2SO4 + 2H2O TABLE OF VALUE Bur Rd|Rough|1st|2nd |3rdFinal|24.00|24.30| 29.30|34.30 Initial|0.00|0.00 |5.00 |10.00 Vol. |24.00|24.30|24.30| 24.30 NOTE: Rough,1st titre,2nd titre,3rd titre are all in (cm3) AVERAGE VOLUME OF ACID USED = 24.30+24.30+24.30/3 = 72.9/3 =24.30. (Bi) A contains 0.125mol/ dm3 of H2SO4(given) ie 0.125 in 1000cm3 of H2SO4 .:. X in 24.30; X = 24.30/1000 * 0.125 = 0.00303 = 0.003 mol per 24.30cm3. (ii) Conc of A * Vol of A/ Conc of B * Vol of B =nA/nB ie CAVA/CBVB = nA/nB = 0.125*24.30/CB*25 = 1/2 CB = 6.075/25 = 0.243 = 0.24mol/dm3. (iii) B contains Xgdm3 of NaOH, Molar Mass of NaOH = 40g. Mass Conc = Mole Concentration * Molar Mass = 0.243 * 40 = 9.72g ====================== ======================= SALT ANALYSIS br /> 2. (a) TEST Xn + Distilled H2O OBSERVATION: White ppt, colourless solution observed. INFERENCE Soluble Salt ======================= (i) *TEST Filterate + BaCl2 + Dil HCl in excess. *OBSERVATION White ppt formed. Precipitate Insoluble. *INFERENCE: SO4^2-,SO3^2-, CO3^2- Present. ======================= TEST: Residue + dilute HCl OBSERVATION: Effervescence gas evolved. An odourless gas. Deep blue ppt. INFERENCE: Cu^2+ Present. ======================= TEST: Filterate + HNO3 + AgNO3 + NH3 *OBSERVATION No visible reaction. White ppt formed. Ppt dissolved in excess NH3(aq) *INFERENCE Cl^- present. Cl^- confirmed. ======================= (bi) TEST Filterate + BaCl2 + dil HCl *OBSERVATION br /> White ppt remained insoluble. *INFERENCE: CO3^2-, SO4^2- Present. ======================= (ii) TEST A portion of (bi) + NaOH solution dropwise and in excess. *OBSERVATION: A light blue ppt insoluble in excess of NaOH Solution. *INFERENCE Cu^2+ present