How would you go about making 250ml of a 20X stock solution of NaCl to dilute later to a final concentration of 50mM? I know that the molecular weight of NaCl is 58.44 but I am not sure where to start. I need to figure out the amount of NaCl and water needed. Thank you!
I got 0.73 grams of NaCl is this correct?
To make a 20X stock solution of NaCl, you need to first calculate the amount of NaCl needed to achieve the desired concentration. Here's how you can do it:
Step 1: Determine the molar concentration of the stock solution.
To obtain a final concentration of 50 mM, you will need the stock solution to be 20 times more concentrated. Therefore, the molar concentration of the stock solution will be 50 mM x 20 = 1000 mM or 1 M.
Step 2: Calculate the moles of NaCl needed.
The moles of NaCl can be calculated using the formula:
moles = concentration (M) x volume (L)
Since you need 250 mL of the stock solution, convert it to liters by dividing it by 1000:
volume = 250 mL / 1000 = 0.25 L
Now, substitute the values into the formula:
moles = 1 M x 0.25 L = 0.25 moles
Step 3: Calculate the mass of NaCl needed.
The mass of NaCl needed can be calculated using the formula:
mass = moles x molecular weight
Since the molecular weight of NaCl is 58.44 g/mol, substitute the values:
mass = 0.25 moles x 58.44 g/mol = 14.61 g
So, you will need 14.61 grams of NaCl to make 250 mL of a 20X stock solution.
Step 4: Calculate the amount of water needed.
To make the stock solution, you will dissolve the calculated mass of NaCl in water. Since the final volume of the stock solution will be 250 mL, the amount of water needed can be calculated by subtracting the mass of NaCl from the total volume:
water volume = 250 mL - 14.61 g = 235.39 mL
Therefore, you will need to add 235.39 mL of water to dissolve the 14.61 grams of NaCl and obtain a 20X stock solution of NaCl with a final concentration of 50 mM.