A solution is prepared by dissolving 10.00 grams of a monobasic salt in a total volume of 1.00 litres. The pH of this solution was measured at 13.07 and a conductivity experiment determined that this salt was completely ionized in solution. What is the molecular weight of this monobasic salt?
I have no idea what to do or how to solve it. please help.Thanks
To solve this question, we need to use a few concepts from chemistry, including pH and molar concentration. I will guide you through the steps to find the molecular weight of the monobasic salt.
Step 1: Determine the concentration of the monobasic salt in the solution.
The question states that 10.00 grams of the monobasic salt is dissolved in a total volume of 1.00 liter. To find the concentration, we need to convert the mass of the salt to moles and then divide by the volume in liters.
First, we need to identify the monobasic salt. Let's assume it is the chloride ion (Cl-).
The molar mass of Cl- is 35.45 g/mol.
To convert the mass of the salt to moles, we divide 10.00 grams by the molar mass of Cl-:
10.00 g / 35.45 g/mol = 0.282 mol
Now, let's calculate the concentration (C) using the formula:
C = number of moles / volume in liters
C = 0.282 mol / 1.00 L = 0.282 M
Step 2: Determine the pOH of the solution.
The pH of the solution is given as 13.07. The pH scale is based on the concentration of hydrogen ions (H+), while the pOH scale is based on the concentration of hydroxide ions (OH-). Since water is neutral and pH + pOH = 14, we can calculate the pOH:
pOH = 14 - pH = 14 - 13.07 = 0.93
Step 3: Calculate the concentration of hydroxide ions.
The pOH is related to the concentration of hydroxide ions (OH-) through the equation:
pOH = - log[OH-]
To find the concentration of OH-, we need to take the antilog (inverse logarithm) of the pOH value. Using a calculator:
[OH-] = 10^(-pOH) = 10^(-0.93) = 0.1246 M
Step 4: Determine the concentration of the monobasic salt.
Since the salt was determined to be completely ionized, the concentration of the monobasic salt is equal to the concentration of the respective ion, which is the chloride ion (Cl-).
[Cl-] = 0.1246 M
Step 5: Calculate the number of moles of the monobasic salt.
We already determined the concentration of the monobasic salt (0.1246 M). To find the number of moles, we multiply the concentration by the volume in liters:
moles of Cl- = [Cl-] × volume in liters = 0.1246 M × 1.00 L = 0.1246 mol
Step 6: Calculate the molecular weight.
Finally, to find the molecular weight (MW) of the monobasic salt, we divide the mass by the number of moles:
MW = mass / moles of Cl- = 10.00 g / 0.1246 mol = 80.23 g/mol
Therefore, the molecular weight of the monobasic salt is approximately 80.23 g/mol.