You need 100. mL of a 9.30-mM solution of a compound whose MW = 438 Daltons. How many grams of solute should you add to the 100 mL?

Be sure to use the right number of significant figures.

To find the number of grams of solute needed, we first calculate the number of millimoles of solute required, then convert that to grams using the molar mass.

1. **Calculate millimoles of solute:**

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

Substituting the given values:

\[
\text{Millimoles of solute} = 9.30 \text{ mM} \times 100. \text{ mL} = 930 \text{ millimoles}
\]

2. **Convert millimoles to moles:**

\[
\text{Moles of solute} = \frac{930 \text{ millimoles}}{1000} = 0.930 \text{ moles}
\]

3. **Convert moles to grams:**

\[
\text{Mass of solute (g)} = \text{Moles} \times \text{Molar mass (g/mol)}
\]

Substituting the values:

\[
\text{Mass of solute (g)} = 0.930 \text{ moles} \times 438 \text{ g/mol} = 407.34 \text{ grams}
\]

4. **Adjust for significant figures:**
   - The volume (100. mL) has 3 significant figures.
   - The molarity (9.30 mM) has 3 significant figures.
   - The molar mass (438 g/mol) has 3 significant figures.
   
Therefore, the result should be expressed with 3 significant figures:

\[
\text{Mass of solute} = 407 \text{ grams}
\]

So, you should add **407 grams** of solute to the 100 mL of solution.

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

1. How would the mass of solute change if the desired solution volume was 50 mL?
2. If you had only 300 grams of the compound, how much solution could you make at the same concentration?
3. What would be the concentration if you dissolved 500 grams of the compound in 100 mL of water?
4. How would the number of grams change if the molar mass was 500 Daltons instead of 438?
5. How many moles of solute are in 1000 mL of the same 9.30 mM solution?

**Tip:** Always double-check the number of significant figures throughout your calculations to ensure your final answer is accurate.

Learn how to calculate the mass of solute required for a 9.30-mM solution using the molarity formula and molar mass conversion. This problem involves converting millimoles to grams and is suitable for advanced high school or college-level chemistry students.

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