how much of khp do you measure out to get a value of 240mg/l

This makes no sense at all. What is khp?

khp is potassium hydogen phthalate I need to know how much to measure out to get a value of 240mg/L for a Bod standard

KHP. Much different that khp.

What volume do you want to make? 200ml, or 45liters?

mass= concentration*volumeDesired
mass= 240mg/liter*VOLUME

need to make up one liter

Add 240 mg to a liter of water. You may end up with a volume > 1 liter. In that case, add more KHP until M(KHP)/240 = V'. Then discard V' - 1 liter, leaving yourself with 1 liter containing 240 mg of KHP.

To determine the amount of KHP (potassium hydrogen phthalate) needed to obtain a value of 240mg/L, we have to consider the molar mass and the desired concentration.

First, you need to know the molar mass of KHP. Potassium hydrogen phthalate has a molar mass of 204.23 g/mole.

The formula to calculate the amount (in grams) of a substance needed to obtain a specific concentration is:

Amount (g) = Concentration (mg/L) x Volume (L) / 1000

In this case, we want to find the amount of KHP required to achieve a concentration of 240mg/L. However, we are not given the volume of the solution, so we cannot determine the exact amount without that information.

Let's say we want to prepare a 1L solution with a concentration of 240mg/L. Using the formula above, we can calculate:

Amount (g) = 240mg/L x 1L / 1000 = 0.24g

Therefore, to prepare a 1L solution with a concentration of 240mg/L, you would measure out 0.24 grams of KHP. Remember to always use appropriate lab techniques and tools, such as a balance, to accurately measure the amount of KHP needed.