Acids react with carbonates, a chemical process fundamental to many everyday phenomena, from baking to natural geological processes. This reaction consistently produces noticeable effects, primarily the formation of a gas.
The Products of the Reaction
When an acid and a carbonate react, they form a salt, water, and carbon dioxide gas. For example, hydrochloric acid reacting with calcium carbonate yields calcium chloride (a salt), water, and carbon dioxide. This reaction neutralizes the acid.
The most visible sign of this reaction is the production of carbon dioxide gas, manifesting as fizzing or bubbling. This effervescence indicates an acid-carbonate reaction. The “salt” produced refers to an ionic compound formed from the positive ion of a base and the negative ion of an acid.
The Chemistry Behind the Fizz
Acids are substances that donate protons (hydrogen ions), while carbonates accept these protons. When an acid encounters a carbonate, it transfers hydrogen ions, leading to the formation of carbonic acid (H₂CO₃).
Carbonic acid is highly unstable in aqueous solutions. It rapidly decomposes into water (H₂O) and carbon dioxide gas (CO₂). This swift decomposition causes the visible fizzing and bubbling as the carbon dioxide gas escapes from the solution.
Where You See Acids and Carbonates Reacting
A common example is the combination of vinegar and baking soda. Vinegar contains acetic acid, and baking soda is sodium bicarbonate, a type of carbonate. When mixed, they vigorously react to produce carbon dioxide gas, water, and sodium acetate.
Antacids relieve heartburn by neutralizing stomach acid. Stomach acid is primarily hydrochloric acid, and many antacids contain carbonates like calcium carbonate or magnesium carbonate. These antacids react with excess stomach acid, producing carbon dioxide gas.
In natural environments, acid rain reacts with limestone structures. Limestone and marble are composed mainly of calcium carbonate. Acid rain, containing acids like sulfuric and nitric acid, corrodes these materials by reacting with calcium carbonate, dissolving the stone and releasing carbon dioxide. This process, known as carbonation, erodes historical buildings and natural rock formations.
Acidic cleaners remove limescale, which is primarily calcium carbonate deposits. Cleaning agents containing acids such as citric acid, acetic acid (vinegar), or hydrochloric acid, react with limescale, dissolving it into soluble compounds that can be easily rinsed away.