A stock standard of urea nitrogen contains 20 mg/mL of urea nitrogen. How much stock is needed to prepare 100 mL of a 20 mg/dL working standard?
Please help!
20 mg/mL = 2000 mg/dL
c1v1 = c2v2
2000*x = 20*100
Solve for x. add that to a 100 mL volumetric flask, add distilled H2O to the mark on the flask, mix thoroughly.
Thank you!
To determine how much stock is needed to prepare a 100 mL working standard, we need to use the concept of dilution.
First, let's understand the relationship between the stock standard and the working standard.
The stock standard contains 20 mg/mL of urea nitrogen, which means that for every 1 mL of the stock, there is 20 mg of urea nitrogen.
The working standard, on the other hand, needs to have a concentration of 20 mg/dL. This means that for every 1 dL (deciliter) of the working standard, there should be 20 mg of urea nitrogen.
Now, let's convert the working standard volume into mL:
1 dL = 100 mL
So, we need to prepare 100 mL of the working standard.
To calculate the amount of stock needed, we can set up a proportion using the concentrations of urea nitrogen:
(20 mg/mL) / X = (20 mg/dL) / 100 mL
Now, we can solve for X (the amount of stock needed):
X = (20 mg/mL) * (100 mL / 20 mg/dL)
X = 100 mL
Therefore, you would need 100 mL of the stock standard to prepare 100 mL of a 20 mg/dL working standard.