Neutralization: Acid + Base Makes Salt + Water

0:00What happens when an acid meets a base?

0:03This beaker holds hydrochloric acid and universal indicator, a mix of dyes that changes colour with pH.

0:11The pH scale usually runs from 0 to 14. Below 7 is acidic, 7 is neutral, and above 7 is basic.

0:21Now add sodium hydroxide, a base, drop by drop.

0:26Watch the indicator. It goes from red, to orange, to yellow, and then to green.

0:33Green means pH 7, which is neutral. This reaction is called neutralization.

0:40To see why, look at the ions. An ion is an atom or group of atoms with an electric charge.

0:47In water, hydrochloric acid splits into hydrogen ions, H plus, and chloride ions, Cl minus.

0:56Sodium hydroxide splits into sodium ions, Na plus, and hydroxide ions, OH minus.

1:04Each hydrogen ion joins a hydroxide ion to make a water molecule.

1:10The sodium and chloride ions are left over. Together they make a salt, sodium chloride.

1:17Here is the full equation: hydrochloric acid plus sodium hydroxide makes sodium chloride plus water.

1:26In chemistry, a salt is any ionic compound made this way, from positive and negative ions.

1:33So salt does not only mean table salt. Potassium nitrate and calcium chloride are salts too.

1:41Antacid tablets contain a base that neutralizes extra stomach acid.

1:46Lime is another base. It raises the pH of acidic soil and lakes.

1:52An acid plus a base makes a salt plus water.