what are the molarities of Mb^2+ ions and Cl- ions in an aqueous solution of 4.00% by the mass magnesium chloride, with a density of 1.15g mL-1?
4% w/w MgCl2 = 4.00 g MgCl2/100 g soln.
volume soln = mass/density = 100g/1.15 g/mL = 86.96 mL.
moles MgCl2 in 4.00 g = 4.00/95.21 = 0.04201 moles.
M Mg^+2 = moles Mg^+2/L soln
M Cl^- = moles Cl^-/L soln.
0.04201/0.08696 = 0.483 M of [Mg^2+]
but how do I get the [Cl-]? the answer is suppose to be 0.966M
To find the molarities of Mb^2+ ions and Cl- ions in the given solution, we need to follow a step-by-step approach. Here's how you can do it:
Step 1: Calculate the mass of MgCl2 in the solution
Given that the solution is 4.00% by mass MgCl2 and the density of the solution is 1.15g mL-1, we need to calculate the mass of MgCl2 present in the solution.
Mass of solution = volume of solution x density
Since the density is given in grams per milliliter (g mL-1), and we want to find the mass of a specific volume, we can use the relationship:
Mass = volume x density
Let's assume we have 100g of the solution. Therefore, the mass of MgCl2 in the solution would be:
Mass of MgCl2 = 4.00% x 100g = 4.00g
Step 2: Convert the mass of MgCl2 to moles
To convert the mass of MgCl2 to moles, we need to know its molar mass. The molar mass of MgCl2 can be calculated by summing the atomic masses of each element in the compound:
Molar mass of MgCl2 = (atomic mass of Mg) + 2 x (atomic mass of Cl)
Using the atomic masses from the periodic table, we find:
Molar mass of MgCl2 = 24.31 + 2 x 35.45 = 95.21 g/mol
Now, we can calculate the number of moles of MgCl2:
Moles of MgCl2 = mass of MgCl2 / molar mass of MgCl2
Moles of MgCl2 = 4.00g / 95.21 g/mol ≈ 0.042 moles
Step 3: Determine the moles of Mb^2+ ions and Cl- ions
In 1 mole of MgCl2, we have 1 mole of Mg^2+ ions and 2 moles of Cl- ions due to the formula of the compound.
Therefore, the moles of Mb^2+ ions = 0.042 moles
The moles of Cl- ions = 2 x 0.042 moles = 0.084 moles
Step 4: Calculate the molarities of Mb^2+ ions and Cl- ions
The molarity (M) is defined as the number of moles of solute per liter of solution.
To calculate the molarity, we need to know the volume of the solution. Let's assume we have 1 liter (1000 mL) of the solution.
The molarity of Mb^2+ ions = moles of Mb^2+ ions / volume of solution (in liters)
Molarity of Mb^2+ ions = 0.042 moles / 1 liter = 0.042 M
The molarity of Cl- ions = moles of Cl- ions / volume of solution (in liters)
Molarity of Cl- ions = 0.084 moles / 1 liter = 0.084 M
So, the molarities of the Mb^2+ ions and Cl- ions in the given solution are 0.042 M and 0.084 M, respectively.