How many grams of KBr dissolved in 100 g of water is needed to raise the boiling point of water to 104.0 C
delta T = i*Kb*molality
i = 2. Solve for molality.
molality = moles/kg solvent
Solve for moles.
moles = grams/molar mass
Solve for grams.
To calculate the number of grams of KBr needed to raise the boiling point of water, we need to use the colligative property known as boiling point elevation. This property states that adding a solute to a solvent will increase the boiling point of the solvent.
The equation to calculate the boiling point elevation is ΔT = K_b * m, where ΔT is the change in boiling point, K_b is the molal boiling point elevation constant, and m is the molality of the solution.
First, let's determine the molal boiling point elevation constant for water. The value for K_b is 0.512 °C/m for water.
Next, we need to calculate the molality (m) of the solution. Molality is defined as the number of moles of solute per kilogram of solvent. In this case, the solvent is water, and we need to find the molality of the KBr solution.
To find the molality, we need to know the molar mass of KBr. The molar mass of K is 39.10 g/mol, and the molar mass of Br is 79.90 g/mol. Adding these values, we get the molar mass of KBr as 39.10 + 79.90 = 119 g/mol.
Assuming that KBr completely dissociates in water, we can calculate the number of moles of KBr required to achieve the desired boiling point elevation.
Let's assume x grams of KBr are dissolved in 100 g of water. The moles of KBr can be calculated as:
moles of KBr = (x grams KBr) / (molar mass of KBr)
The molality (m) is then calculated as:
m = (moles of KBr) / (kilograms of water)
Since we know that the mass of water is 100 g, we can convert it to kilograms by dividing by 1000:
m = (moles of KBr) / (0.1 kg)
Now, let's use the equation ΔT = K_b * m to calculate the change in boiling point (ΔT), which is equal to the desired boiling point (104.0 °C) minus the boiling point of pure water (100.0 °C).
ΔT = 104.0 °C - 100.0 °C = 4.0 °C
Now, we can rearrange the equation and solve for moles of KBr:
moles of KBr = (ΔT * 0.1 kg) / K_b
Finally, we can calculate the mass of KBr required using the moles of KBr and the molar mass of KBr:
mass of KBr = (moles of KBr) * (molar mass of KBr)
So, to find the grams of KBr needed to raise the boiling point of water to 104.0 °C, you can use the aforementioned calculations.