Calculate the new molarity when 150 mL of water is added to 125 mL of 8.55 M HBr.

To calculate the new molarity, we need to use the formula:

M1V1 = M2V2

Where:
M1 = initial molarity
V1 = initial volume
M2 = final molarity
V2 = final volume

In this case, the initial molarity (M1) is 8.55 M, the initial volume (V1) is 125 mL, and the final volume (V2) is the sum of the initial volume and the volume of water added (125 mL + 150 mL = 275 mL).

Substituting the given values into the formula:

8.55 M × 125 mL = M2 × 275 mL

Now, let's solve for M2 (the final molarity):

(8.55 M × 125 mL) / 275 mL = M2

M2 ≈ 3.9 M

Therefore, when 150 mL of water is added to 125 mL of 8.55 M HBr, the new molarity is approximately 3.9 M.