0.1802 g sample of a chlorocarbon compound was analyzed by burning in oxygen and collecting the evolved gases in a solution of sodium hydroxide. After neutralizing, the sample was treated with 39.50 mL of a 0.025 M AgNO3. This precipitated the Cl- as AgCl and left an excess of silver nitrate. This excess required 27 mL of 0.006 M KSCN in a Volhard titration. Calculate the %w/w Cl (MM = 35.45 g/mol) in the sample. [Answer in 2 decimal places]
Given:
Cl- + AgNO3 → AgCl + NO3-
AgNO3 + KSCN → AgSCN + KNO3
millimols AgNO3 initially = 39.50 mL *0.025 M = ?
mmols KSCN used to back titrate = 27.0 x 0.006 M = ?
Subtract initial mmols - back titrated mmols = difference which is the amount AgNO3 used; i.e., it's the mmols AgCl produced.
Convert to mols, change to grams Cl, calculate % w/w by
%chloride = (g Cl/mass sample)*100 = ?
how do you convert mmols to mols?
Divide by 1000.
mols = millimoles/1000
To calculate the percent w/w of chlorine (Cl) in the sample, we need to determine the amount of chlorine (in grams) in the sample and divide it by the mass of the sample, and then multiply by 100.
Step 1: Calculate the moles of AgNO3 used in the titration.
Given:
Volume of AgNO3 used (V1) = 39.50 mL = 0.03950 L
Molarity of AgNO3 used (M1) = 0.025 M
Using the formula: moles = volume x molarity
moles of AgNO3 (n1) = V1 x M1
moles of AgNO3 (n1) = 0.03950 L x 0.025 mol/L
Step 2: Calculate the moles of KSCN used in the titration.
Given:
Volume of KSCN used (V2) = 27 mL = 0.027 L
Molarity of KSCN used (M2) = 0.006 M
Using the formula: moles = volume x molarity
moles of KSCN (n2) = V2 x M2
moles of KSCN (n2) = 0.027 L x 0.006 mol/L
Step 3: Calculate the moles of Cl that corresponds to the excess AgNO3.
Since AgNO3 reacts in a 1:1 ratio with Cl-, the moles of Cl can be determined from the moles of AgNO3 used in excess.
moles of Cl (n3) = n1
Step 4: Calculate the moles of Cl that reacted with KSCN.
Since AgNO3 and KSCN react in a 1:1 ratio, the moles of Cl can be determined from the moles of KSCN used.
moles of Cl (n4) = n2
Step 5: Calculate the moles of Cl in the sample.
The moles of Cl in the sample can be calculated by subtracting the moles of Cl that reacted with KSCN from the moles of Cl that corresponds to the excess AgNO3.
moles of Cl in the sample = n3 - n4
Step 6: Calculate the mass of Cl in the sample.
Mass of Cl = moles of Cl x molar mass of Cl
Mass of Cl = moles of Cl x 35.45 g/mol
Step 7: Calculate the mass of the sample.
Given:
Mass of the sample = 0.1802 g
Step 8: Calculate the percent w/w of Cl in the sample.
Percent w/w of Cl = (Mass of Cl / Mass of the sample) x 100
Plug in the values calculated in the previous steps and calculate the final answer, rounding to 2 decimal places.