Neutralization of hydrochloric acid with sodium hydroxide

Objectives

• Carry out a neutralization reaction.
• Use an indicator to find when the acid is used up.
• Show that neutralization is exothermic.

Theory

An acid reacts with a base to form a salt and water. The reaction between H⁺ and OH⁻ ions releases heat (about 57 kJ per mole of water formed). Phenolphthalein is colourless in acid and pink above pH 8.2, so the first permanent pink colour shows that all the acid has reacted.

HCl + NaOH → NaCl + H₂O

Procedure

1. Put on your safety goggles and lab coat.
2. Place a conical flask on the bench.
3. Add 25 mL of dilute hydrochloric acid to the flask.
4. Add a few drops of phenolphthalein.
5. Place a thermometer and record the starting temperature.
6. Add sodium hydroxide solution a little at a time until the solution just stays pink.
7. Record the temperature again.

Precautions

• Wear goggles.
• Add the alkali in small portions near the end point and swirl.

Subject

Chemistry

Grade

9–10

Chapter

Acid, Base and Salt (Nepal National Curriculum (CDC), grade 10)

Difficulty

Easy

Duration

15 min

Safety level

Medium

Version

1.0

Apparatus

• Conical flask (250 mL)
• Thermometer

Chemicals

• Dilute hydrochloric acid HCl Corrosive
• Sodium hydroxide solution NaOH Corrosive
• Phenolphthalein indicator C₂₀H₁₄O₄