A student is asked to prepare 400.0 mL of a 0.25M HCl solution. The students find a bottle labeled ""2.0M HCl."" How many mL of the 2.0M solution are needed to prepare the 0.25M solution?

The answer to your question is He needs 50 ml of 2.0 M HCl.

Explanation:

Data

Volume 2 = 400 ml

[HCl] 2 = 0.25 M

[HCl] 1 = 2.0 M

Volume 1 = ?

To solve this problem use the dilution formula

Formula

                     V₁C₁  =  V₂C₂

Solve for V₁

                     V₁ = V₂C₂ / C₁

Substitution

                      V₁ = (400)(0.25) / 2

Simplification

                      V₁ = 100 / 2

Result

                      V₁ = 50 ml

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)