Question

A chemist combines 11 grams of sodium with 14 grams of chlorine. A spectacular reaction occurs and produces sodium chloride. After the reaction, the chemist finds that all the chlorine was used up by the reaction, but 2 grams of sodium remained. How many grams of sodium chloride were formed?

Short answer

After the reaction, 9 grams of sodium reacted with 14 grams of chlorine to form 23 grams of sodium chloride.

Step-by-step solution

Calculate the amount of sodium that reacted

Subtract the mass of sodium that remained after the reaction from the total mass of sodium initially present to find out how much sodium actually took part in the reaction.

Determine the mass of sodium chloride produced

Since all the chlorine was used up and the reaction was complete, the mass of sodium chloride produced is the sum of the mass of chlorine used and the mass of sodium that reacted.

Key concepts

Understanding Chemical Reactions

Chemical reactions are processes where substances, known as reactants, transform into different substances called products. For example, when sodium (Na) reacts with chlorine (Cl) to form sodium chloride (NaCl), sodium and chlorine are the reactants, and sodium chloride is the product. This transformation involves breaking old chemical bonds and forming new ones, releasing or absorbing energy in the process.

When learning about chemical reactions, it's crucial to grasp the visual and symbolic representations, namely, chemical equations. A balanced chemical equation reflects the process that occurs during a chemical reaction. It is important for students to learn how to balance these equations, as it ensures that the number of atoms of each element involved remains the same before and after the reaction, complying with the law of conservation of mass.

The Law of Conservation of Mass

The law of conservation of mass states that matter cannot be created or destroyed in an isolated system. During a chemical reaction, the mass of the products equals the mass of the reactants. This principle is critical to solving stoichiometry problems.

For instance, in the reaction where sodium combines with chlorine to form sodium chloride, the total mass of sodium and chlorine before the reaction must equal the total mass of sodium chloride and any excess reactants after the reaction. If a chemist starts with 11 grams of sodium and uses up all 14 grams of chlorine, the total mass of the reactants is 25 grams. Therefore, even after 2 grams of sodium remains unreacted, the mass of the sodium chloride produced plus the 2 grams of sodium must equal 25 grams.

The Mole Concept in Stoichiometry

The mole concept is pivotal in chemistry as it provides a bridge between the atomic scale and the macroscopic world we can measure in the laboratory. One mole corresponds to Avogadro's number (\(6.022 \times 10^{23}\)), which is the number of particles found in 12 grams of carbon-12. This number is used to count atoms, ions, or molecules in a given substance.

In stoichiometry problems, chemists use the mole concept to calculate the quantities of reactants and products involved in a chemical reaction. For example, they can convert grams to moles to predict how much of a product will form from a given number of moles of reactants. This involves using molar masses, which are derived from the periodic table, as conversion factors. Understanding the mole concept allows students to interpret and balance chemical equations in terms of the actual number of particles involved, and to accurately predict the mass of substances produced in a reaction.