Video Transcript
A metal oxide and an acid reacted together to form zinc chloride and water. What were the metal oxide and the acid?
In this problem, we are trying to identify the metal oxide and the acid in the beginning of the experiment. Let us identify the formulas for the products that were formed. The products are zinc chloride and water. Let us begin by writing the formula for zinc chloride. The ions that make up zinc chloride or the zinc ion with a charge of two plus and the chloride ion which has a charge of one minus. When the charges are crossed and the signs are dropped the formula for zinc chloride would be ZnCl2 and the formula for water is H2O.
In order to begin to set up formulas for the reactants we need to identify, let us first discuss oxides, which are compounds that contain at least one oxygen atom chemically bonded to an atom of another element. Therefore, the metal oxide would have an anion of oxygen. When referring to the term acid, we can consider Brønsted–Lowry acids which is a substance that can lose or donate protons, H+ ions, in a reaction. So we know that acid will have a hydrogen ion within the molecule.
In order to identify the metal oxide on the reactant side as well as the acid, let us review the law of conservation of mass, which states matter cannot be created nor destroyed. This means the number and type of atoms on the reactant side must equal the number and type of atoms on the product side. To identify the metal in the metal oxide, we can look at the metal on the product side.
To identify the metal on the product side, let us take a look at the periodic table. Elements to the left of the metalloids staircase are metals, with the exception of hydrogen which is a nonmetal, and elements to the right of the metalloids staircase are classified as nonmetals. Within the product side of the chemical reaction, there are four different types of atoms: Zn, zinc; Cl, chlorine; H, hydrogen; and O, oxygen. Only Zn, zinc, is the metal. Therefore, the metal oxide is zinc oxide.
Now let us write the formula for zinc oxide. The ions that make up zinc oxide are the zinc ion with a charge of two plus and the oxygen ion which has a charge of two minus. When the charges are crossed and the signs are dropped, we have a formula of Zn2O2. Notice the ratio of two zinc ions and two oxygen ions. Therefore, we can reduce the formula to ZnO.
Now let us identify the acid. The acid needs to contain the anion or nonmetal. On the product side, the nonmetal that has not been used within the reactants is the chloride ion, Cl. Now let us write the formula for the acid. The ions that make up the acid are the hydrogen ion with a charge of one plus and the chloride ion, which has a charge of one minus. When the charges are crossed and the signs are dropped, the formula for the acid is HCl. And the name of this acid is hydrochloric acid.
When taking a look at the chemical equation as written, it is important to notice that it is not balanced and therefore not abiding by the law of conservation of mass. In order to correct this problem, a coefficient of two can be placed in front of HCl, hydrochloric acid. So we have determined that the metal oxide and acid that react to produce zinc chloride and water are zinc oxide and hydrochloric acid.
