[Ice-cream]

hey can any1 help me with these questions:

1. The solubility of oxygen in water at 298K and 1atm pressure is 3.5e-4mol/L. What is the concentration of oxygen in equilibrium with air at 298K? Assume that the mole fraction of oxygen in air is 0.2. [ans: 7e-5mol/L]

i realise that i'd have to use C = kP but the problem is, im not sure exactly what i should be aiming to do. I did some random substituting and got the ans. but the problem is, i don't think i actually understand what is going on!

2. A 100g sample of water at 80 degrees C is mixed with 10g of ice cubes at 0degrees C. THe heat of fusion of ice is 335J/g, and the specific heat of liquid water is 4.18J/g degrees C. Calculate the final temperature in degrees C of the mixture. [ans: 65]

what i think is that the heat released from the water should be equal to the heat gained by the ice-cubes...but then i dont understand why the heat of fusion of ice is given because the ice will melt...and ignoring it doesnt seem to give me the ans.

3.  A calorimeter with a heat capacity of 4.61kJ/K contains 18050g of freon-12. Benzoic acid is combusted in the calorimeter and liberates 26400J of heat energy causing the temperature to rise 3 degrees C. Calculate the specific heat of freon-12 in J/g degrees C. [ans: 0.2]

can any1 give me some starting tips...im really stuck with this one!

[xiankai]

2) u have to include the heat of fusion of ice because as u know, when ice melts the temperature will be constant until it completely melts.

Heat to melt Ice + Heat to raise temp. of melted ice = Heat lost by water

3) specifict heat capacity is defined as the amount of heat required to raise a specific amount of mass by one celsius (or kelvin if u prefer)

looking at that, bear in mind heat is lost to the calorimeter too. so,

heat gained by calorimeter + heat gained by freon-12 = heat liberated by combustion of benzoic acid.