The density of acetonitrile, CH3CN, is 0.786 g/mL, and the density of methanol, CH3OH, is 0.791 g/mL.
A solution is made by dissolving 15.0 g of methanol in 250.0 mL of acetonitrile. Assuming that the
volumes of the solute and solvent are additive, what is the molarity of methanol in the solution?
mass = volume x density or
v = m/d
v methanol = 15.0 g/0.791 g/mL = 19.0 rounded.
v acetonitrile = 250 mL.
Total volume = 269 mL
moles CH3OH = grams/molar mass = 15.0/32 = 0.469 rounded
molarity = M = moles/L solution = 0.469/0.269 = ?
Check my arithmetic.
To find the molarity of methanol in the solution, we first need to determine the number of moles of methanol present.
Step 1: Determine the volume of solution
The volume of the solution is given as 250.0 mL.
Step 2: Convert the mass of methanol to moles
The mass of methanol is given as 15.0 g. To convert this to moles, we need to know the molar mass of methanol (CH3OH).
The molar mass of carbon (C) is 12.01 g/mol, the molar mass of hydrogen (H) is 1.01 g/mol, and the molar mass of oxygen (O) is 16.00 g/mol. Using the periodic table, we can calculate the molar mass of methanol as follows:
Molar mass of CH3OH = (12.01 g/mol × 1) + (1.01 g/mol × 4) + (16.00 g/mol + 1) = 32.04 g/mol
Now, we can calculate the number of moles of methanol by dividing the mass by the molar mass:
Number of moles of methanol = 15.0 g ÷ 32.04 g/mol
Step 3: Calculate the molarity
To calculate the molarity, we divide the number of moles of methanol by the volume of the solution in liters:
Molarity of methanol = (Number of moles of methanol) / (Volume of solution in liters)
Volume of solution in liters = 250.0 mL ÷ 1000 mL/L
Now, plug in the values:
Molarity of methanol = (15.0 g ÷ 32.04 g/mol) / (250.0 mL ÷ 1000 mL/L)
Simplifying the equation gives us:
Molarity of methanol = (0.468 mol) / (0.250 L)
Finally, calculate the molarity:
Molarity of methanol ≈ 1.87 M
Therefore, the molarity of methanol in the solution is approximately 1.87 M.