Question

Given stock solutions of 25 mM nitrophenyl phosphate, and 1.5 M tris,pH 7.2, 7.5 mM MgCl2. If you mix 0.1ml of the nitrophenyl phosphate, 0.7 ml of the tris solution and 0.2 ml of water to bring the total volume to 1 ml, what is the final concentrations of each of the components in the final solution? Show work

Nitrophenyl phosphate in mM

Tris in M

Magnesium chloride in mM

Answer 1

In the given question, we are adding 0.1ml of the nitrophenyl phosphate, 0.7 ml of the tris solution and 0.2 ml of water to bring the total volume to 1 ml.

Total volume = 1 ml

We need to first calculate the no of mmols in 0.1ml of the nitrophenyl phosphate

Molarities of Stock solutions of nitrophenyl phosphate, tris,pH 7.2 and MgCl₂ will give us the No. of moles of each species in 1 Lt of Volume.

Molarity= No. of moles dissolved in 1 Lt of solution

So, 25 mM nitrophenyl phosphate will contain 25 mmols of nitrophenyl phosphate in 1 Lt of volume.

1 lt (1000 ml) of 25 mM nitrophenyl phosphate solution will contain = 25 mmols of nitrophenyl phosphate

0.1ml of 25 mM nitrophenyl phosphate solution will contain= 0.1 * 25 /1000 = 25* 10^-4 mmoles ofnitrophenyl phosphate

Similarly

1.5 M tris(pH 7.2) will contain 1.5 mols (1500 mmols) of tris in 1 Lt of volume.

0.7 ml of 1.5 M tris(pH 7.2) solution will contain= 0.7* 1.5 /1000 = 1.05* 10^-3 moles oftris

So we are adding 25* 10^-4 moles ofnitrophenyl phosphate and 1.05* 10^-3 mols oftris and making the total volume 1 ml by diluting with water.

Now we will calculate the molarity,

For nitrophenyl phosphate :

1 ml of total volume contains = 25* 10^-4 mmoles ofnitrophenyl phosphate

1000 ml of total volume will contain = 25* 10^-1mmoles ofnitrophenyl phosphate or 2.5 mmols

Concentration of nitrophenyl phosphate = 2.5 mmoles/Lt = 2.5mM

For Tris:

1 ml of total volume contains = 1.05* 10^-3 moles oftris

1000 ml of total volume will contain = 1.05 moles oftris

Concentration of tris = 1.05 moles/Lt = 1.05 M

Since we have not added MgCl2 in given question, its Concentration will be zero.