Question

The molality of a solution that is made by dissolving a certain mass of benzene in 20.6g of carbon tetrachloride is 0.529m. How many moles of benzene were dissolved?

Answer 1

Answer:

0.0108  moles of benzene were dissolved

Explanation:

Molality is a unit of measure to express the concentration of a solution. A solute is a substance that dissolves in a solvent with which it forms a solution and is found in a smaller proportion than the solvent in a solution. A solvent is the substance that dissolves a solute, forming a solution and is found in greater proportion than the solute in a solution. Therefore the molality indicates the relationship between the number of moles of any solute dissolved per kilograms of solvent:

$Molality=\frac{Moles of solute}{Kilograms of solvent}$

Molality is expressed in units (moles / Kg).

Molality is independent of pressure and temperature.

Then, knowing the mass of solvent and molality, it is possible to calculate the moles of the solute, in this case of benzene:

Moles of solute=Molality * Kilograms of solvent

In that case the solvent is carbon tetrachloride and its mass is 20.6 g. As you need to know its mass in kg, you must perform the conversion, taking into account that 1000 g= 1 kg. Then 20.6 g=0.0206 kg

So:

• Molality=0.529
• Kilograms of solvent= 0.0206

Then:

Moles of solute=0.529*0.0206

Moles of solute=0.0108

Finally, 0.0108  moles of benzene were dissolved

Answer 2

Molality of solution = 0.529 m

mass solvent in kg = 20.6 g => 20.6 / 1000 => 0.0206 kg

number of moles = molality x mass solvent

= 0.529 x 0.0206 =>  0.0108 mol benzene 

hope this helps!