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1725QUIZ1FALL2004solutions

# 1725QUIZ1FALL2004solutions - Qi7L W,r\r;r 1.725 Quiz...

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Qi7L W# \,r\r;r 1.725 Quiz Solutions 1. a) Volume of rain = (15m)(lm)(0.05m) = 0.75 m 3 = 750-L . (O.kg salt/750L)*(26 gmol Na 4 Fe(CN) 6 /kg salt) '3.5* 10 9 M Na 4 Fe(CN) 6 b) [CNT] = [HCN] + [CN'] (we are considering after photolysis) from mass action, [H*][CN']/[HCN]= 10 '9 plug in pH 6.9, which gives [CN']/[HCN] = 10 '2' 1 = .0079 fraction = .0079/(1+.0079) = .008 c) Initial flux density is given by J = -k*Cinitia Assuming complete photolysis, and knowing that most of the CNTis present as HCN (from part b), [HCN] = S[Na 4 Fe(CN) 6 ] = 1.7*10-8 M. J = (1 cm/hr)(1.7* 108 mol/1000 cm 3 ) = 1.7*10 ' " mol/cm 2 hr (note that the puddle depth is an unnecessary piece of information) 2. a) definition of Henry's constant: H = C.JCw.,,, C, = Ca/H = (0.2 atm)/(540 L atm mol-') = 3.7* 10 4 mol/L b) The system is at steady state, so flux in = flux out. Specifically, the rate of 02 production via photosynthesis equals the rate of 02 removal through air-water exchange. In variables: Jo = k([2]1,, - [O2]qui) Air-water exchange will be water-side controlled (can either recognize that °2 is 20% of air, so it will be limited by the water, or calculate dimensionless H = 22 > 10'2).

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1725QUIZ1FALL2004solutions - Qi7L W,r\r;r 1.725 Quiz...

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