Which of the following is the correct procedure to prepare a dilute hydrochloric acid solution from a concentrated stock solution?

• A. Heat the concentrated HCl before diluting with water.
• B. Mix concentrated HCl with sodium chloride before adding water.
• C. Add the required amount of concentrated HCl to water slowly while stirring.
• D. Add water to the concentrated HCl all at once.

Answer: (C)

Verified step by step guidance

1. Understand that when diluting a concentrated acid, the process is exothermic, meaning it releases heat.
2. Recognize that adding water directly to concentrated acid can cause the mixture to splash or boil violently due to rapid heat release.
3. Therefore, the correct procedure is to add the concentrated acid slowly to a larger volume of water while stirring continuously to dissipate heat safely.
4. Avoid heating the concentrated acid before dilution, as this is unnecessary and can be dangerous.
5. Avoid mixing concentrated acid with other solids like sodium chloride before dilution, as this does not affect the dilution process and can be unsafe.