[Science Form 2] Difference Of Acids & Alkalis

Scientists use something called the pH scale to measure the strength of an acidic or alkaline liquid. Although there may be many types of ions in a solution, the pH focuses on the concentration of hydrogen ions (H⁺) and hydroxide ions (OH^-). The scale goes from values very close to 0 through 14.

Distilled water is 7. Acids can have a pH of between 0 and a number very close to below 7, while alkalis have a pH of between a number very close to above 7 and 14.

Most of the liquids we find every day have a pH near 7. They are either a little below or above that mark. If we go into a chemistry lab, we could find solutions with a pH of 1 and others with a pH of 14.

There are also very strong acids with pH values of below 1, such as battery acid. Alkalis with pH values of near 14 include drain cleaners and sodium hydroxide (NaOH). These chemicals are corrosive and very dangerous.

Also you can easily tell if a substance is an acid or not by its effect on litmus paper. Blue litmus paper is used for testing acids. If wet blue litmus paper turns red, the substance is acidic. Wet red litmus paper is used to test alkalis, which will turn the paper blue.

Properties of acids and alkalis that distinguish them from other substances

Acids

• have a sour taste and feel like water.
• turn litmus solution red, as well as turn blue litmus paper red.
• have pH numbers less than 7.
• react with metals, forming hydrogen and a salt.
• react with carbonates, forming a salt, water and carbon dioxide.
• react with alkalis, forming a salt and water.

Alkalis

• feel soapy to touch and taste bitter.
• turn litmus solution blue, as well as turn red litmus paper blue.
• have pH numbers greater than 7.
• react with ammonium compounds to give off ammonia gas (except for ammonia).
• react with acids, forming a salt and water.
• do not react with metals and carbonates.