Question

1.When a sample of 0.242 grams of an unknown substance containing chloride (Cl-) was boiled and was analyzed and it was found to contain 0.084 gram of Cl- ion. Calculate the % chloride in in the substance. 6. Below is the overall equation of the reaction of Co 3+ with thiosulfate. 2 Co(NH3)4Cl3 + 2

2.Below is the overall equation of the reaction of Co 3+ with thiosulfate.
2 Co(NH3)4Cl3 + 2 S2O3 2- ----------> 2 Co 2+ + S4O6 2- + 8 NH3 + 6 Cl –
Use the overall equation to calculate what size sample should be measured so as to react with 25 mL 0.1500M Na2S2O3

Answer 1

We know the mass of sample = 0.242 g

Mass of chloride in it = 0.084 g

So mass percent of Cl-

= ( 0.084 / 0.242 ) x 100 = 34.7 %

2)

Calculation of mass of Co(NH3)4Cl3

Volume of thiosulfate = 0.025 L , molarity of thiosulfate = 0.15 M

Moles of thiosulfate = volume in L x molarity = 0.025 L x 0.15 M = 0.00375 mol

Mol ratio bbetween thiosulfate and Co(NH3)4Cl3 is 2 : 2

Therefore mol of Co(NH3)4Cl3

= moles of thiosulfate x 2 moles of Co(NH3)4Cl3 / 1 mol thiosulfate

= 0.00375 mol Co(NH3)4Cl3

Molar mass of Co(NH3)4Cl3 = 233.4143 g/mol

Mass of Co(NH3)4Cl3 in g = mol x molar mass

=0.00375 mol x 233.4143g /mol

= 0.875 g

So the mass of Co(NH3)4Cl3 in g = 0.875 g