You have been asked to prepare a stock solution of phosphate

You have been asked to prepare a stock solution of phosphate buffer. The working solution is 0.1M and the stock solution should be 100x more concentrated. What is the molar concentration of the stock solution? If the molecular weight of the sodium phosphate is 100 and you are asked to make 4 liters, how would you do this?

Solution

Ans:

The molar concentration of the stock solution should be 10 Molar

From the data given is

Concentration of working phosphate buffer is 0.1 M

The stock should be 100 times more than the working concentration, hence

The stock solution= 0.1 x 100x

                             = 10.0 M stock.

Answer for Part-2

The MW of sodium phosphate =100

100gm in 1000ml gives 1 M or 1x Phosphate buffer

For Preparing 10M stock we require 100gm x 10M

There for 1000gm In 1 liter will give 100x concentration

Fro preparing 100x stock of 4 liters phosphate buffer we require 4x 1000gm in 4 liters

4kg of Sodium phoasphate dissolved in 4000ml water.

After complete mixing, top up final solution to 10 L. The pH of the 10X stock is will be approximately 6.8, but when diluted to 1x PBS it should change to 7.4.When making buffer solutions, it is good practice to always measure the pH directly using a pH meter. If necessary, pH can be adjusted using hydrochloric acid or sodium hydroxide.