In the chlorine titration of a solution prepared by the dissolution of 0.2110 g of commercial hypochlorite was spent 19.50 ML of sodium thiosulphate solution 0.1002 mol/L. Calculate the percentage of chlorine (35.45 g/mol) in this sample
Did you add KI and titrate the liberated I2 with Na2S2O3?
yes
I assume you want percent Cl2 (note that is 70.9 g/mol).
Cl2 + 2I^- ==> 2Cl^- + I2
OCl^- + 2I^- + 2H^+ ==> I2 + Cl^- + H2O
I2 + 2S2O3^2- ==> S4O6^2- + 2I^-
mols S2O3^2- => M x L = ?
mols S2O3^2- x 1/2 = mols I2 = mols Cl2
grams Cl2 = mols Cl2 x molar mass Cl2.
% Cl2 = (g Cl2/mass sample)*100 = ?
To calculate the percentage of chlorine in the sample, we need to first determine the amount of chlorine in moles. We can use the equation:
Hyochlorite (ClO-) + 2H+ + 2e- → Chlorine (Cl2) + H2O
The balanced equation tells us that for every mole of hypochlorite (ClO-) present, we produce one mole of chlorine (Cl2). Therefore, the moles of chlorine can be calculated using the balanced equation and the amount of sodium thiosulphate (Na2S2O3) used in the titration.
Step 1: Calculate the moles of sodium thiosulphate (Na2S2O3) used
Moles of Na2S2O3 = Volume of Na2S2O3 (in L) * Concentration of Na2S2O3 (mol/L)
Given:
Volume of Na2S2O3 used = 19.50 mL = 19.50/1000 L = 0.0195 L
Concentration of Na2S2O3 = 0.1002 mol/L
Moles of Na2S2O3 = 0.0195 L * 0.1002 mol/L = 0.0019569 mol
Step 2: Calculate the moles of chlorine
From the balanced equation, we know that 2 moles of electrons are required to convert 1 mole of hypochlorite (ClO-) to 1 mole of chlorine (Cl2).
Since Na2S2O3 acts as an electron donor in the titration, the number of moles of chlorine is equal to half the number of moles of Na2S2O3 used in the reaction.
Moles of Cl2 = Moles of Na2S2O3 / 2 = 0.0019569 mol / 2 = 0.00097845 mol
Step 3: Calculate the mass of chlorine
Mass of Cl2 = Moles of Cl2 * Molar mass of Cl2
Molar mass of Cl2 = 2 * Molar mass of chlorine (Cl)
Molar mass of chlorine (Cl) = 35.45 g/mol
Molar mass of Cl2 = 2 * 35.45 g/mol = 70.90 g/mol
Mass of Cl2 = 0.00097845 mol * 70.90 g/mol = 0.069416 g
Step 4: Calculate the percentage of chlorine
Percentage of chlorine = (Mass of Cl2 / Mass of sample) * 100
Given:
Mass of sample = 0.2110 g
Percentage of chlorine = (0.069416 g / 0.2110 g) * 100 = 32.90%
Therefore, the percentage of chlorine in the sample is approximately 32.90%.