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Q. Molarity of 720g of pure water -

      (1) 40 M                                                  (2) 4 M

      (3) 55.5 M                                               (4) Unpredictable

Dear student,
Molarity is a concentration term hence is independent of total amount of solution. 720g pure water means (720/18) moles or in other words 40 moles. Now density of water is 1g/mL hence volume of 720g water is 720 mL.
Molarity is amount of moles of solute present in 1000 mL solution. Here solute and solvent both is water since it is pure water.

Hence ;
720 mL contains 40 moles,
1000 mL contains 40720×1000 = 55.55 moles
Hence molarity is 55.55 M. Answer is (3)

Hope it helps.
Regards

  • 33
Molarity of pure water is always 55.5M
  • -1
By formula 
molarity = given weight /molar mss*1000/given volume in ml
M=760/18*1000/760
M=1.316*42.22
M=55.5644444~55.55
there fore molarity of 760g of pure water is 55.55M 
  • 6
Molarity = 720g ? 18g/mol *( 1000/720) which gives molarity = 55.55M
  • 0
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