Question

B.WATER SAMPLE ANALYSIS.

Water temperature 27°C.

SAMPLE 1

a)Volume of Na2S2O3 required to titrate water sample; Final buret reading : 12.7mL, Initial buret reading= 2.6mL,Volume of Na2S2O3=10.1mL.

b)Moles of Na2S2O3 required to titrate water sample(show calculations)=_________mol.

c)Moles of O2 present in 200mL of water sample(show calculations)________mol.

d)Grams of O2 present in 200mL of water sample=_______g.

e)Milligrams of O2 present in 200mL of water sample=________mg.

f)Milligrams of O2 present in 1000mL of water sample=______ppm.

g)Saturation level for yourwater sample(show calculations)=_________ppm.

Answer 1

b) n(Na₂S₂O₃) = C(Na₂S₂O₃) x V = C(Na₂S₂O₃) mol/L x 0.0101 L

c) 1 mol of O₂ reacts with 4 mol S₄O₆^2- (8 mol S₂O₃^2-)

d) m(O₂) = n(O₂) x Mr(O₂) = n(O₂) mol x 32 g/mol

e) 1 gram = 1000 mg

m(O₂) x 1000

f) In 1000 mL O₂ m(O2) x 1000 x 5

g) Percent saturation (% saturation) is the amount of dissolved oxygen in the water sample compared to the maximum amount that could be present at the same temperature