How many moles of NaCl are found in 500 mL of a buffer solution containing 300 mM NaCl?

• A. 7.5 x 10^-3
• B. 3.0 x 10^-3
• C. 3.0 x 10^-2
• D. 1.5 x 10^-1

Answer: (D)

To determine the number of moles of NaCl in a 500 mL buffer solution with a concentration of 300 mM, it's important to understand the relationship between molarity, volume, and moles. Molarity (M) is defined as the number of moles of solute per liter of solution.

First, convert the volume of the solution from milliliters to liters. Since there are 1000 mL in 1 L, 500 mL is equivalent to 0.5 L.

Next, recall that concentration in millimolar (mM) can be converted to molarity by noting that 1 mM equals 0.001 M. Therefore, 300 mM is equivalent to 0.3 M.

Now, use the formula:

[

\text{moles of solute} = \text{molarity} \times \text{volume in liters}

]

Substituting the known values:

[

\text{moles of NaCl} = 0.3 , \text{M} \times 0.5 , \text{L} = 0.15 , \text{moles}

]

To express