When hydrochloric acid and zinc are combined, they create hydrogen gas and zinc chloride, which is a salt. It is a single replacement reaction where zinc replaces the hydrogen.
To perform this experiment, a scientist begins by adding a small amount of hydrochloric acid to a Petri dish or a flask. A small piece of zinc metal is then added to the hydrochloric acid. When the zinc is introduced to the hydrochloric acid, it rapidly bubbles and produces hydrogen gas. If a scientist puts a balloon over the flask, it will capture the hydrogen gas and expand.
The interaction of the hydrochloric acid and zinc is called an oxidation-reduction reaction. It is also referred to as a redox reaction. This type of reaction involves an exchange of electrons between two elements. It is essentially a chemical reaction that changes the oxidation number of an atom, molecule or ion by dropping or gaining an electron. Oxidation occurs when electrons are lost while reduction takes place when electrons are gained. Oxidation-reduction reactions are common in nature, and they occur in many basic life processes. Respiration, corrosion, rusting and photosynthesis are all examples of redox reactions. The oxidation state of an element refers to the number of electrons that an atom uses, loses or gains when it combines with another compound. To determine an atom's oxidation state, scientists use seven standard rules. In neutral compounds, the sum of oxidation states should be zero. The sum of oxidation states should equal the charge in polyatomic ions.
Oxidation-reduction reactions break down into four types: combination and decomposition, single and double displacement, combustion and disproportionation. The reaction of zinc and hydrochloric acid is specifically a combustion reaction, which is also called an exothermic reaction. Exothermic reactions always involve oxygen, and they always generate heat. Reactions that generate heat and light are called burning reactions. In most cases, exothermic reactions involve a chemical being oxidized by oxygen. In exothermic reactions, less energy is used to break bonds in the reactants than to form new bonds in the resulting product. Other examples of exothermic reactions are burning firewood and nuclear energy production.
The hydrogen gas that zinc and hydrochloric acid produce has many uses. Hydrogen is one of the most abundant elements in the universe, and it plays a role in many daily life functions. On Earth, it is present in water and in molecules that form living organisms. Hydrogen also exists in stars and planets. It has no taste, color or odor, and is one of the least-dense gases. Hydrogen gas is flammable but it requires oxygen to ignite. Hydrogen serves many practical uses in society because it is versatile and fairly easy to produce. Hydrogen is a primary component of many types of energy and does not produce toxic emissions when used as a fuel cell. It is produced from biomass, fossil fuels and renewable sources of energy. It is also used to produce ethanol and can power electric vehicles. Due to its practical applications, hydrogen is also used in the industrial sector and even in the military.