o make 100mL of a solution that is .25M in chloride ion, how many grams of MgCl2 would you need to dissolve
To determine the number of grams of MgCl2 needed to make a 100mL solution that is 0.25M in chloride ion, you will need to follow these steps:
Step 1: Understand the concept
Molarity (M) is defined as the number of moles of solute per liter of solution. To calculate the number of moles, you can use the formula:
Moles = Molarity × Volume (in liters)
Step 2: Convert the volume to liters
In this case, the volume given is 100mL. You need to convert it to liters by dividing by 1000:
Volume (in liters) = 100mL ÷ 1000 = 0.1L
Step 3: Calculate the moles of chloride ion
Since MgCl2 dissociates to form two chloride ions (Cl-), the moles of chloride ions will be twice the molarity:
Moles of chloride ion = 0.25M × 0.1L × 2 = 0.05 moles
Step 4: Calculate the molar mass of MgCl2
The molar mass of MgCl2 can be found by summing the atomic masses of magnesium (Mg) and two chlorine atoms (Cl):
Molar mass of MgCl2 = (1 × atomic mass of Mg) + (2 × atomic mass of Cl)
Using the atomic masses of Mg (24.31 g/mol) and Cl (35.45 g/mol):
Molar mass of MgCl2 = (24.31) + (2 × 35.45) = 95.21 g/mol
Step 5: Calculate the mass of MgCl2
You can now calculate the mass of MgCl2 needed using the moles of chloride ion and the molar mass:
Mass of MgCl2 = Moles of chloride ion × Molar mass of MgCl2
Mass of MgCl2 = 0.05 moles × 95.21 g/mol ≈ 4.7605 grams
Therefore, you would need approximately 4.7605 grams of MgCl2 to dissolve in water to make a 0.25M chloride ion solution with a volume of 100 mL.