A chemist has 12.0 M HBr and would like to use it to make 500.0 mL of 3.5 M HBr. describe how she should do this

mL x M = mL x M

mL x 12.0 = 500 x 3.5
mL = you can do it---about 60 mL or so.

The reason I worked it through is to show you what NOT to do. You DON'T use 60 mL of the concd soln (or whatever the number turns out to be) and add 500 mL of water. Instead, you take 60 (or whatever) and add to water to make a total of 500 mL of solution. On an exam, that is the tricky part. The prof will want to see that you have written that the total solution is 600 mL, not 60 mL added to 540 mL because volumes are not additive and in accurate work you may not assume they are.

1.5 x 10(10) mL

To make 500.0 mL of 3.5 M HBr using a 12.0 M HBr solution, the chemist can follow these steps:

1. Calculate the amount of solute required:
- Use the formula: C1V1 = C2V2
- C1: Initial concentration = 12.0 M
- V1: Initial volume (unknown)
- C2: Final concentration = 3.5 M
- V2: Final volume = 500.0 mL = 0.500 L
- Rearrange the formula to solve for V1:
V1 = (C2 * V2) / C1
V1 = (3.5 M * 0.500 L) / 12.0 M
V1 ≈ 0.1458 L or 145.8 mL

2. Measure 145.8 mL of the 12.0 M HBr solution using a pipette or a graduated cylinder.

3. Transfer the measured 145.8 mL of the 12.0 M HBr solution into a volumetric flask.

4. Add distilled water to the flask, slowly, while swirling, until the volume reaches 500.0 mL mark on the flask.

5. Mix gently to ensure proper mixing of the solution.

The chemist now has 500.0 mL of a 3.5 M HBr solution.

To make a 500.0 mL solution with a concentration of 3.5 M HBr using the 12.0 M HBr solution, the chemist needs to dilute the concentrated solution with an appropriate volume of solvent. Here's how she should do it:

1. Determine the required amount of solute (HBr) needed for the desired concentration:
Concentration of desired solution = 3.5 M
Volume of desired solution = 500.0 mL = 0.5000 L

We can use the equation that relates concentration, volume, and amount (moles) of solute:
M1V1 = M2V2

Rearranging the equation to solve for the required amount of solute:
Amount of solute (moles) = Concentration × Volume
Amount of solute (moles) = 3.5 M × 0.5000 L

The chemist needs 1.75 moles of HBr for the desired solution.

2. Calculate the volume of the concentrated solution required to obtain the desired amount of HBr:
M1V1 = M2V2

Rearranging the equation to solve for V1 (the volume of concentrated solution):
V1 = (M2 × V2) / M1
V1 = (12.0 M × 0.5000 L) / 3.5 M

The chemist needs 1.714 L (or 1714 mL) of the 12.0 M HBr solution.

3. Take a container (graduated cylinder or volumetric flask) and add 1.714 L (or 1714 mL) of the 12.0 M HBr solution. Ensure an accurate measurement.

4. Add distilled water slowly to the container while gently mixing the solution. Continue adding water until the final volume reaches 500.0 mL (or 0.5000 L).

5. Once the solution is thoroughly mixed, verify its concentration using a suitable method like titration or measuring its pH.

By following these steps, the chemist can accurately prepare 500.0 mL of a 3.5 M HBr solution using the 12.0 M HBr solution.