a solution of 30 percent by weight has a density of 0.96g/mL at 25 degree celcius.find the molarity and molality.
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You are going to have a tad of the thinking yourself. I will be happy to critique your work. Of course, you have to know 30 percent by mass of WHAT.
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To find the molarity and molality of a solution, we need to know the mass of solute and the volume of solvent. In this case, the given information is the density of the solution.
First, let's find the mass of the solution. Since we have a 30% solution by weight, this means that 30 grams of solute are present in 100 grams of solution.
Therefore, we can calculate the mass of the solution as follows:
Mass of solution = 100 grams
Next, we need to determine the mass of the solute in the solution. We can use the density and volume to find this.
Density = mass/volume
Rearranging the equation, we get:
Mass = Density * Volume
Given that the density of the solution is 0.96 g/mL, and assuming a volume of 100 mL (which is equivalent to 100 grams for water), we can calculate the mass:
Mass = 0.96 g/mL * 100 mL = 96 grams
Now that we know the mass of the solute (30 grams) and the mass of the solution (96 grams), we can calculate the mass of the solvent:
Mass of solvent = Mass of solution - Mass of solute
= 96 grams - 30 grams
= 66 grams
To find the molarity, we need to know the molecular weight of the solute. Assuming the solute is a salt, we can use the molar mass of that compound. Since you haven't specified the solute, let's assume it is NaCl (sodium chloride).
The molecular weight of NaCl is 58.44 g/mol.
Molarity (M) = Moles of solute / Volume of solution in liters
First, we need to find the moles of solute. We can use the mass and molecular weight:
Moles of solute = Mass of solute / Molecular weight
= 30 grams / 58.44 g/mol
≈ 0.514 mol
Now, we convert the volume of solution (100 mL) to liters:
Volume of solution = 100 mL / 1000 mL/L = 0.1 L
Finally, we can calculate the molarity:
Molarity (M) = 0.514 mol / 0.1 L
= 5.14 M
Now let's calculate the molality.
Molality (m) = Moles of solute / Mass of solvent in kilograms
First, we need to convert the mass of the solvent to kilograms:
Mass of solvent = 66 grams / 1000 g/kg
= 0.066 kg
Now we can calculate the molality:
Molality (m) = 0.514 mol / 0.066 kg
= 7.79 m
Therefore, the molarity of the solution is approximately 5.14 M and the molality is approximately 7.79 m.