To find the number of millimoles of solute in 392 mL of a 67.8 mM solution, we can use the formula:

$\text{{Millimoles of solute}} = \text{{Molarity (mM)}} \times \text{{Volume (mL)}}$

Substituting the given values:

$\text{{Millimoles of solute}} = 67.8 \text{{ mM}} \times 392 \text{{ mL}}$

Calculating this:

$\text{{Millimoles of solute}} = 26,577.6 \text{{ millimoles}}$

Considering significant figures:

• The volume (392 mL) has 3 significant figures.
• The molarity (67.8 mM) has 3 significant figures.

Therefore, the result should also be expressed with 3 significant figures:

$\text{{Millimoles of solute}} = 26,600 \text{{ millimoles}} \quad \text{(rounded to 3 significant figures)}$

So, there are 26,600 millimoles of solute in the solution.

Would you like more details or have any questions? Here are some related questions you might find interesting:

1. How would the number of millimoles change if the volume was increased to 500 mL?
2. What is the molarity if the same number of millimoles is dissolved in 1 liter of solution?
3. How many grams of solute are present if the molar mass is 58.44 g/mol?
4. What is the volume required to have 1000 millimoles of solute at the same concentration?
5. How would the concentration change if 200 mL of water were added to the solution?

Tip: Always ensure the number of significant figures in your final answer reflects the precision of the given data.