To make 10 mL of 25 mM sodium standard, what volume of 1 M NaCl stock should be used?

250 mL
2.5 mL
0.25 mL
0.5 mL
None of these
400 mL

Hmmm. mM? is that milliMolar?

If so, you are diluting it 1/.025 times, or 40 times, so you need 1 part stock, 39 parts water.

1/40 th of 10 ml is 10ml/40= .25ml stock

check my thinking

To determine the volume of 1 M NaCl stock needed to make a 10 mL solution with a concentration of 25 mM, we can use the formula:

C1V1 = C2V2

Where:
C1 = concentration of the stock solution (1 M NaCl)
V1 = volume of the stock solution needed (unknown)
C2 = desired concentration of the final solution (25 mM)
V2 = volume of the final solution (10 mL)

In this case, we want to find V1.

Rearranging the formula:

V1 = (C2 * V2) / C1

Substituting the given values:

V1 = (25 mM * 10 mL) / 1 M

Now we can calculate the volume of the 1 M NaCl stock needed:

V1 = (25 * 10) / 1000
V1 = 0.25 mL

Therefore, the correct answer is 0.25 mL.