Thursday 2 May 2013

Determine the amount of CaCl2 (i = 2.47) dissolved in 2.5 litre of water such that its osmotic pressure is 0.75 atm at 27°C.


Determine the amount of CaCl2 (i = 2.47) dissolved in 2.5 litre of water such that its osmotic pressure is 0.75 atm at 27°C.
Solution
Given that
Osmotic pressure π = 0.75 atm
Volume V = 2.5 liter
van’t Hoff factor i =  2.47
T = 27 +  273  = 300 K
Let w is the amount of CaCl2 required
Gas constant R = 0.0821 L atm K-1mol-1
Molar mass of CaCl2M = 1 × 40 + 2 × 35.5 = 111g mol-1
Use the formula of osmotic pressure
 
Plug the values in this formula we get
W  = 3.43 g
Answer
Required amount of CaCl2 = 3.42 g.

2 comments:

  1. Why did we take volume 2.5
    Shouldn't we take cool of solution

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    Replies
    1. Its because the mass of CaCl2 is negligible and does nothing to raise the volume noticeably.
      Thats why we take Volume of Water alone neglecting the mere 3.42g of CaCl2

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