sea water 0.470 M NaCl 0.068 M MgCl2 25℃ osmotic 100.0 atm 1.00 L

sea water 0.470 M NaCl 0.068 M MgCl2 25℃ osmotic 100.0 atm 1.00 L

 

 

Desert countries like Saudi Arabia have built reverse osmosis plants

to produce fresh water from seawater.

 

Assume that seawater has the composition

0.470 M NaCl and 0.068 M MgCl2

and that both compounds are completely dissociated.

 

a) What is the osmotic pressure of seawater at 25℃?

 

b) If the reverse osmosis equipment can exert

a maximum pressure of 100.0 atm at 25.0℃,

what is the maximum volume of fresh water

that can be obtained from 1.00 L of seawater?

 

---------------------------------------------------

 

a) What is the osmotic pressure of seawater at 25℃?

 

NaCl(aq) → Na^+(aq) + Cl^-(aq) ---> i = 2

MgCl2(aq) → Mg^2+(aq) + 2Cl^-(aq) ---> i = 3

 

2(0.470) + 3(0.068) = 1.144 M

---> 전체 이온의 몰농도

 

 

 

π = MRT

( 참고 https://ywpop.tistory.com/1921 )

 

= (1.144) (0.08206) (273.15+25)

= 27.99 atm

 

 

 

 

b) If the reverse osmosis equipment can exert

a maximum pressure of 100.0 atm at 25.0℃,

what is the maximum volume of fresh water

that can be obtained from 1.00 L of seawater?

 

from 보일의 법칙: PV = P’V’

---> πV = π’V’

 

 

 

압력이 가해질 때 생산되는

진한 용액(= 폐수)의 부피를 계산하면,

V’ = πV / π’

= (27.99 atm) (1.00 L) / (100.0 atm)

= 0.2799 L

 

 

 

담수의 부피를 계산하면,

1.00 - 0.2799 = 0.7201 L

 

 

 

답: a) 28.0 atm, b) 0.72 L

 

 

 

 

[ 관련 글 https://ywpop.tistory.com/7231 ] 해수 담수화

 

 

 

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