What is the molality of 5.4g of potassium chloride (KCl) dissolved in 250 g of water?
To find the molality (m) of a solution, you need to know the amount of solute (in moles) and the mass of the solvent (in kilograms).
Step 1: Convert the mass of potassium chloride (KCl) from grams to moles.
To do this, you need to know the molar mass of KCl. The molar mass of K (potassium) is approximately 39.1 g/mol, and the molar mass of Cl (chlorine) is approximately 35.5 g/mol. Adding these two masses together gives us the molar mass of KCl, which is approximately 74.6 g/mol.
Use the formula:
moles of KCl = mass of KCl / molar mass of KCl
moles of KCl = 5.4 g / 74.6 g/mol
Step 2: Convert the mass of water from grams to kilograms.
We have 250 g of water that needs to be converted to kilograms. Since 1 kg is equal to 1000 g, we divide 250 g by 1000 to get the mass of water in kilograms.
mass of water = 250 g / 1000 = 0.25 kg
Step 3: Calculate the molality.
Molality is defined as the moles of solute per kilogram of solvent.
m = moles of solute / mass of solvent in kilograms
m = moles of KCl / mass of water in kg
Now, substitute the values we calculated earlier:
m = (5.4 g / 74.6 g/mol) / 0.25 kg
Calculating this expression will give us the molality (m) of the potassium chloride (KCl) solution.