Calculate the molality of a 10% H3PO4 solution in water.
To calculate the molality of a solution, you need to know the amount of solute (in moles) and the mass of the solvent (in kilograms). In this case, the solute is H3PO4 (phosphoric acid) and the solvent is water.
Step 1: Determine the amount of solute in moles.
To find the amount of H3PO4 in moles, you need to know the molar mass of H3PO4. The molar mass of phosphoric acid is:
(3 * atomic mass of Hydrogen) + (1 * atomic mass of Phosphorus) + (4 * atomic mass of Oxygen)
= (3 * 1.01 g/mol) + (1 * 31.0 g/mol) + (4 * 16.0 g/mol)
= 98.0 g/mol
Now, calculate the amount of H3PO4 in grams using the given percentage.
If you have 10% H3PO4 solution, it means that there are 10 grams of H3PO4 in every 100 grams of the solution.
So, for every 100 grams of the solution, 10 grams are H3PO4.
Step 2: Convert grams of H3PO4 to moles.
To convert grams to moles, divide the mass of H3PO4 by its molar mass.
Mass of H3PO4 = 10 grams
moles of H3PO4 = (mass of H3PO4) / (molar mass of H3PO4)
= 10 g / 98.0 g/mol
Step 3: Determine the mass of the solvent in kilograms.
Given that the solvent is water, we will assume it to be 1000 grams (1 kilogram) for simplicity.
Step 4: Calculate the molality.
Molality (m) is defined as the moles of solute per kilogram of solvent.
molality = (moles of solute) / (mass of solvent in kg)
= (moles of H3PO4) / (mass of water in kg)
= (10 g / 98.0 g/mol) / 1 kg
Now, perform the calculation to get the molality value.