# Fish need at least 4ppm dissolved O2 for survival.?

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Fish need at least 4ppm dissolved O2 for survival.

1) What is this concentration in mol/L?

2) What partial pressure of O2 above the water is needed to obtain thi concentration at 10*C? (The Henry’s law constant for O2 at this temperature is 1.71 x 10^-3mol/l x atm.)

• 1) the 4 ppm means 4 grams of O2 for every 1,000,000 grams of sea water.

convert 4 grams O2 into moles

= 4 g / (32 grams of O2 per mole of O2) <— molecular mass of O2 is 32 grams

= 4 / 32

= 0.125 moles of O2

scale down to 1 liter (aka 1,000 grams)

= 0.125 moles * (1,000 grams / 1,000,000 grams)

= 0.125 moles / 1,000 grams

= 1.25 * 10^-4 moles of O2 per 1,000 grams of sea water

``          and since 1,000 grams is 1 liter``

= 1.25 * 10^-4 moles O2 per L sea water

2) 1.25 10^-4 moles/L = P 1.71 10^-3 moles / (L atm)

``````           where P - pressure of O2 above the water

P = (1.25 * 10^-4) / (1.71 * 10^-3) atm``````

P = you calculate

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