March 27, 2015

Homework Help: Chemistry

Posted by Bryant on Sunday, March 6, 2011 at 11:42pm.

Hi DrBob,
Sorry about that, I wasn't very clear!

Can someone please help me complete these calculations for my lab; I am having some trouble.

A. Standardization of Na2S2O3
-Mass of KIO3 in 100mL = 0.09600g
-Calculate Molarity of KIO3= ?
Please check: 0.09600g/(214.0g/mol)=4.486x 10^-4 mol
-4.486 mol/0.1L= 0.004486 M

B. Titration/ Volume of Na2S2O3
1: 38.44 mL
2: 37.23 mL
3: 38.11 mL
Average Volume: 37.93mL

-Calculate molarity of Na2S2O3=?
Not sure what to use as the mass here? Help

C. V of Bleach= 1.020 mL
V of Na2S2O3= 2.010 mL
Calculate Mass of NaOCl/100mL bleach=? Help with this.
-We are told here from the concentrations and volume of the added sodium thiosulfate solution used to titrate, calculate the numbers of moles of the oxidizing agent present, assuming it to be sodium hypochlorite, NaOCl. Use this to calculate the number of grams of sodium hypochlorite that was present in the 0.5mL of bleach.

The equation for I2 is: KIO3 reacts w/ excess KI in the following reaction:
IO3 + 5I + 6H--> 3I2 + 3H20
2S2O3 + I2 --> 2I + S406

Sodium Hypochlorite reacts with sodium thiosulfate in the following reaction:
NaClO + 2H + 2I--> I2 + Cl + H20+ Na
2S203 + I2 --> 2I + S406


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