The image you uploaded contains a titration problem for calculating the concentration of an HCl solution. Here’s a summary and solution approach based on the content visible:

Problem Overview:

• A titration was performed, and 19.90 mL of 0.157 M NaOH was needed to neutralize 25.0 mL of HCl.
• The balanced chemical equation is: $\text{HCl(aq)} + \text{NaOH(aq)} \rightarrow \text{NaCl(aq)} + \text{H}_2\text{O(l)}$ This indicates a 1:1 molar ratio between HCl and NaOH.

Formula to Use:

• The problem suggests using the titration formula: $M_A V_A = M_B V_B$ where:
  • $M_A$ is the molarity of HCl (unknown),
  • $V_A$ is the volume of HCl (25.0 mL),
  • $M_B$ is the molarity of NaOH (0.157 M),
  • $V_B$ is the volume of NaOH (19.90 mL).

Solution Steps:

1. Rearrange the formula to solve for $M_A$: $M_A = \frac{M_B V_B}{V_A}$
2. Substitute the values: $M_A = \frac{0.157 \times 19.90}{25.0}$
3. Perform the calculation: $M_A = \frac{3.1243}{25.0} = 0.12497 \, \text{M} \approx 0.125 \, \text{M}$

Answer: The concentration of the HCl solution is approximately 0.125 M.

Would you like more detailed steps or explanations? Here are 5 related questions you might explore:

1. What are the units for molarity and why are they important?
2. How does the 1:1 molar ratio between HCl and NaOH affect the calculation?
3. Could this method be used if the molar ratio were not 1:1?
4. What is the significance of the balanced chemical equation in titration problems?
5. How would you handle experimental errors in a real titration process?

Tip: Always ensure volumes are in the same units when applying the titration formula.