Potassium dichromate has several industrial applications. To determine the purity of the salt that will be used in different industrial processes, a sample mass equal to 2.660 g was dissolved and quantitatively transferred to a 500.00 mL flask. An aliquot of 25.00 mL of this solution was treated with excess KI and the released iodine was titrated with 0.1000 mol L-1 sodium thiosulfate, spending 27.00 mL. Calculate the purity of the analyzed salt. Data: K = 39.10 O = 16.00 Cr = 52.00 I = 126.9 S = 32.07
Potassium dichromate has several industrial applications. To determine the purity of the salt that will be used in different industrial processes, a sample mass equal to 2.660 g was dissolved and quantitatively transferred to a 500.00 mL flask. An aliquot of 25.00 mL of this solution was treated with excess KI and the released iodine was titrated with 0.1000 mol L-1 sodium thiosulfate, spending 27.00 mL. Calculate the purity of the analyzed salt.
Data:
K = 39.10 O = 16.00 Cr = 52.00 I = 126.9 S = 32.07
KI or I-(aq) reduces potassium dichromate, K2Cr2O7 to Cr3+(aq) and itself gets oxidized to I2.
The balanced equation is:
K2Cr2O7(aq) + 7H2SO4(aq) + 6KI(aq) -----> 4K2SO4(aq) + Cr2(SO4)3(aq) + 7H2O(l) + 3I2(aq)
Now I2(aq) reacts with sodium thiosulfate, Na2S2O3 accordin the reaction given below:
2 Na2S2O3(aq) + I2(aq) ----> Na2S4O6(aq) + 2NaI(aq)
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