Calculate the molality, % percent composition by weight, and the mole fraction of HCl in an aqueous 12M HCl solution that has a density of 1.20 g?mL
Please help :(
12M HCl means 12 mols HCl/L solution.
Use density to convert L solution to grams. That is approximately 1200 grams (water + HCl). You know how much the HCl weighs; it is 12 mols or 12*36.5 = about 440g. Therefore, the water must have a mass of 1200-440 = about 762 or 0.762 kg.
molality = mols/kg solvent.
I'm confused about what you want in % composition. If you mean % HCl it is
(mass HCl/mass 1L)*100 = ? . However, when one asks for %composition one USUALLY means %H, %Cl.
For mols fraction,
You have mols HCl. Convert g solvent to mols. Then XHCl = nHCl/total mols.
Post your work if you get stuck. You need to confirm each step in the above since I've estimated here and there.
Assume 12 moles of HCL per liter:
To solve for the molarity first, compute the total weight of the solution. Since, molarity is equal to moles/liter, assume that you have a total volume of 1L. 1L converted to mL is equal to 1.00 x10 ^3 mL. This multiplied by the density is equal to a 1.20 x10^3 g. Since you now know the amount of moles in your solution and the total weight, you can figure out the molality (moles/weight in Kg); convert g to kg before computing the answer.
Assume 12 moles of HCL per liter:
12 moles*36.46g/mole = the number of grams of HCl per liter.
Divide your answer for grams obtained for HCl by the total weight. Make sure that you are dividing g/g or Kg/Kg to obtain %w/w.
Assuming the 12M HCl solution is made with H2O, subtract the weight of HCl that you obtained from the total weight; this gives you the number of grams of H20. Since the molecular weight of H2O is 18g/mole, divide the weight that you obtained for H20 by the molecular weight for H2O (g of H2O/18g) to obtain the number of moles of H20. To get the mole fraction divide the moles of HCl by the moles of HCL plus the moles of H2O.
moles of HCL/(moles of HCL +moles of H20) = mole fraction.
Did not know that you were posting an answer.
Correction, you have to subtract the grams of HCL from the total weight before calculating molality.
Excuse my typos as well.
Sure, I can help you with that! To calculate the molality, percent composition by weight, and mole fraction of HCl in the solution, we'll need to follow a series of steps.
1. Calculate the molality (m):
The molality is defined as the number of moles of solute per kilogram of solvent. In this case, the solute is HCl and the solvent is water. To calculate the molality, we need to know the mass of HCl and water.
Given:
Concentration of HCl solution (C) = 12 M
Density of HCl solution (D) = 1.20 g/mL
To find the mass of HCl (m_HCl), we can use the formula: mass = density * volume.
The volume of 1 liter (1000 mL) of the solution can be calculated using the formula: volume = mass / density.
Since the solution is 12 moles of HCl in 1 liter (1000 mL) of solution, we can convert moles to grams using the molar mass of HCl.
Step 1: Calculate the mass of HCl:
Mass_HCl = volume * density * molar mass of HCl
= (1000 mL) * (1.20 g/mL) * (36.461 g/mol)
= 43,753.2 g
Step 2: Calculate the molality:
Molality (m) = moles of solute / mass of solvent (in kg)
Since the density is in grams per milliliter, we need to convert it to kilograms per liter:
Mass_water = volume * density
= (1000 mL) * (1.00 g/mL)
= 1000 g
Now, we can calculate the molality:
m = (12 mol HCl) / (1000 g H2O / 1000)
= 12 mol / 1 kg
= 12 mol/kg
2. Calculate the percent composition by weight:
Percent composition by weight is the ratio of the mass of the solute to the total mass of the solution, expressed as a percentage.
Step 1: Calculate the mass of the solution:
Mass_solution = Mass_HCl + Mass_water
= 43,753.2 g + 1000 g
= 44,753.2 g
Step 2: Calculate the percent composition by weight:
Percent composition (%) = (mass of HCl / mass of solution) * 100
= (43,753.2 g / 44,753.2 g) * 100
= 97.76%
3. Calculate the mole fraction of HCl:
The mole fraction of a component in a solution is the ratio of the moles of that component to the total moles of all components.
Step 1: Calculate the moles of HCl:
Moles_HCl = mass of HCl / molar mass of HCl
= 43,753.2 g / 36.461 g/mol
= 1200 mol
Step 2: Calculate the total moles of all components (HCl + water):
Total moles = Moles_HCl
Step 3: Calculate the mole fraction of HCl:
Mole fraction_HCl = Moles_HCl / Total moles
= 1200 mol / 1200 mol
= 1
So, the results are:
Molality (m) = 12 mol/kg
% Composition by weight = 97.76%
Mole Fraction of HCl = 1
Please note that the calculations assumed that the volume given for the density is in liters (L). If the given volume is in a different unit, the volumes and hence, the results, will need to be adjusted accordingly.