Calculating Freezing Point Depression with Urea and Water

In summary, to lower the freezing point by 1.60 degrees celsius, 0.861 moles of urea (MW = 60.056 g/mol) would need to be dissolved in 1 kg of water. To calculate the grams required, multiply the mole amount by the molar mass of urea.
  • #1
parwana
182
0
How many grams of urea (MW = 60.056 g/mol) would have to be dissolved in 115.0 grams of water to lower the freezing point by 1.60 degrees celsius?

Equation for freezing point
Tf= Kf x Cm

Kf= 1.858
Cm= molality of solute in kg

please help, iam getting the same answer
 
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  • #2
Here, [itex]T_f[/itex] is 1.60, and from there you can calculate the molality:

[tex]T_f=K_f \times C_m and C_m=\frac {T_f}{K_f}[/tex]

[tex]C_m=\frac {1.60}{1.858}=0.861[/tex]

Since your molality is 0.861, it means that in 1 kg of solution you'll have to dissolve moles of this amount of compound.
 
  • #3
i still don't kn ow how to calculate the grams required, please help
 
  • #4
What did you find as mole amount from the last equation I gave? You'll just multiply this value with molar mass of urea to learn how many grams should be in the solution.
 

1. What is the freezing point?

The freezing point is the temperature at which a liquid changes into a solid state, also known as the melting point in reverse. It is the temperature at which the molecules in a substance slow down enough to form a solid crystal structure.

2. How is the freezing point determined?

The freezing point can be determined by measuring the temperature of a substance as it is slowly cooled. As the temperature decreases, the molecules in the substance will begin to arrange themselves in a regular, crystalline pattern. The temperature at which this occurs is the freezing point.

3. Does every substance have the same freezing point?

No, the freezing point of a substance depends on its chemical composition and molecular structure. Different substances have different freezing points, which can vary from below -100°C to above 100°C.

4. Can the freezing point be affected by external factors?

Yes, the freezing point of a substance can be affected by external factors such as pressure, impurities, and the presence of other substances. For example, adding salt to water will lower the freezing point, causing it to freeze at a lower temperature.

5. Why is the freezing point important in science?

The freezing point is an important physical property of a substance that can provide valuable information about its molecular structure and behavior. It is also essential in many industrial processes, such as freezing food and creating materials like glass and metals, as well as in weather forecasting and understanding the behavior of Earth's atmosphere and bodies of water.

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