calculate the volume of 4.0 M hydrochloric acid needed to make

100.0 mL of 0.10 M hydrochloric acid.

.100 L * .10 M/L = .010 M

.010 M / 4.0 M/L = ?

How many mols do you want? That's mols = M x L = 0.1 x 0.1 = ?

Then M HCl = mols/L. You know M = 4.0M and you know mols = ? from above, solve for L of the 4.0 M stuff. There is an easier way to do it. You should get the same answer eithr way.
mL1 x M1 = mL2 x M2
100 x 0.1 = mL2 x 4.0
mL2 = ?
(Note: Procedure 1 gives volume in L and procedure 2 gives volume in mL).

To calculate the volume of 4.0 M hydrochloric acid needed to make 100.0 mL of 0.10 M hydrochloric acid, we can use the formula:

C₁V₁ = C₂V₂

Where:
C₁ = Initial concentration of hydrochloric acid
V₁ = Initial volume of hydrochloric acid
C₂ = Final concentration of hydrochloric acid
V₂ = Final volume of hydrochloric acid

In this case:
C₁ = 4.0 M
V₁ = ?
C₂ = 0.10 M
V₂ = 100.0 mL

Let's rearrange the formula to solve for V₁:

V₁ = (C₂V₂) / C₁

Now we can plug in the given values to find the volume V₁:

V₁ = (0.10 M * 100.0 mL) / 4.0 M

V₁ = 1.0 mL

Therefore, you would need to add 1.0 mL of the 4.0 M hydrochloric acid to make 100.0 mL of 0.10 M hydrochloric acid.