How many grams of NaOH is needed to make 4 L of a solution with a pH of 7.4?(molecular wt. of NaOH is 40 g/M)?

Question

Please show me all the calculations so that I can understand how to solve this problem. Thanks!

Answer 1

Hee are the steps, you can do the calculations

A pH of 7.4 has a pOH of 6.6 (total is 14)

The concentration of OH ions is the reverse base 10 log of -6.6.

Once yu have the conc. of OH ions, it is stated in moles per liter. You have 4 liters, so multiply the moles by 4.

Each mole of NaOH gives 1 mole of OH ions, so it is one to one. Now multiply by 40 g / mol to get the number of grams required.

Answer 2

As pH = 12.0, So pOH = 14 - 12 = 2.0 Therefore [OH-] = 10^-pOH = 10^-2 M So for making 2.50 L of NaOH solution with a pH of 12, we have to prepare !0^-2 M NaOH solution. Moles of NaOH = 2.50 L x 10^-2 mol L-1 = 0.025 mol So grams of NaOH = 40 x 0.025 = 1.0 g

Answer 3

First, recall pH + pOH = 14.

If the pH = 7.4, then

pOH = 14 - 7.4
pOH = 6.6

[OH] = antilog (- pOH]

antilog is the inverse log on your calculator.

[OH] = 3.0 x 10^-7 M, where M is the molarity

So,

[OH] = moles of solute of NaOH / L of solution

3.0x10^-7 = moles of NaOH / 4 L of solution * 40 g/mol NaOH

Solve for NaOH

4 L * 3.0^10-7 moles NaOH / L * 40 g/mol NaOH =

4.8x10^-5 grams of NaOH

Now, check your work:

Although NaOH is a strong base, the pH = 7.4. Therefore, the concentration of NaOH is so small, that the water is basically neutralizing the NaOH.