We need to add 2.09 mL of concentrated acid to obtain 75 mL of 0.335 M HBr solution.
You are performing a dilution of HBr going from a concentration of 12M to 0.335M, and you want to end up with a final volume of 75 ml of the dilute solution.
Consider the dilution formula: M1V1 = M2V2.
The basis behind this formula is that the number of moles of the acid before and after the dilution must remain constant.
M1 = the molarity of the stock solution,
M2 = the molarity of the diluted solution,
V2 = the final volume of the diluted solution.
In this case, we need to determine V1, which is the volume of the stock solution used to prepare the diluted sample. With this knowledge, we can plug our numbers into the equation and we obtain the following:
(12 mol/L)*V1 = (0.335mol/L)*(0.075L).
Keeping in mind that molarity is the moles of a substance in one liter of solution, we will use mol/L instead of M. By doing this, we are reminded that in order to use this equation, we must convert 75 mL into units of liters.
After rearranging the equation and solving for V1, we find that V1 = 0.00209L.
Finally, we must convert back from liters to mL by multiplying the final answer by 1000.
This way we end up with V1 = 2.09 mL.
This means that we need to add 2.09 mL of concentrated acid to obtain 75 mL of 0.335 M HBr solution.
Learn more about molarity here: brainly.com/question/23243759
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