Question

You are working in the laboratory, preparing sodium chloride. Consider the following results for three preparations of the compound: Case \(1: 39.34 \mathrm{~g} \mathrm{Na}+60.66 \mathrm{~g} \mathrm{Cl}_{2} \longrightarrow 100.00 \mathrm{~g} \mathrm{NaCl}\) Case \(2: 39.34 \mathrm{~g} \mathrm{Na}+70.00 \mathrm{~g} \mathrm{Cl}_{2} \longrightarrow\) $$ 100.00 \mathrm{~g} \mathrm{NaCl}+9.34 \mathrm{~g} \mathrm{Cl}_{2} $$ Case \(3: 50.00 \mathrm{~g} \mathrm{Na}+50.00 \mathrm{~g} \mathrm{Cl}_{2} \longrightarrow\) $$ 82.43 \mathrm{~g} \mathrm{NaCl}+17.57 \mathrm{~g} \mathrm{Na} $$ Explain these results in terms of the laws of conservation of mass and definite composition.

Short answer

The results confirm the law of conservation of mass and the law of definite composition: the total mass of reactants equals the total mass of products, and NaCl is formed in a fixed ratio of Na to Cl.

Step-by-step solution

- Understanding the Conservation of Mass

The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. This means that the total mass of reactants must equal the total mass of products in a chemical reaction.

- Analyzing Case 1

In Case 1, 39.34 g of Na reacts with 60.66 g of Cl₂ to form 100.00 g of NaCl. Here, the total mass of reactants (39.34 g + 60.66 g) equals the mass of the product (100.00 g), which conforms to the law of conservation of mass.

- Analyzing Case 2

In Case 2, 39.34 g of Na reacts with 70.00 g of Cl₂. The products are 100.00 g of NaCl and 9.34 g of Cl₂. The total mass of reactants (39.34 g + 70.00 g) equals the total mass of products (100.00 g + 9.34 g), which is 109.34 g. Again, this respects the conservation of mass.

- Analyzing Case 3

In Case 3, 50.00 g of Na reacts with 50.00 g of Cl₂. The products are 82.43 g of NaCl and 17.57 g of unreacted Na. The total mass of reactants (50.00 g + 50.00 g) equals the total mass of products (82.43 g + 17.57 g), which is also 100.00 g, confirming the conservation of mass.

- Understanding the Law of Definite Composition

The law of definite composition states that a chemical compound always contains its component elements in a fixed ratio by mass. This explains why the mass of NaCl remains constant in cases where all of the Na reacts with Cl₂.

- Applying the Law of Definite Composition to Case 1

In Case 1, the mass ratio of Na to Cl in NaCl is maintained as 39.34:60.66, which adheres to the law of definite composition.

- Applying the Law of Definite Composition to Cases 2 and 3

In Case 2, an excess of Cl₂ is present, which results in the same fixed ratio of Na to Cl forming NaCl, with leftover Cl₂. In Case 3, an excess of Na is present, resulting in the same fixed ratio forming NaCl, with leftover Na.

Key concepts

chemistry fundamentals

Chemistry fundamentals form the basis of understanding chemical reactions and the interactions between different substances. At its core, chemistry is about studying the properties of matter and how it changes. One essential aspect is understanding that matter is composed of atoms and molecules. These small particles bond in specific ways to form compounds. This bonding and interaction result in chemical reactions.

Chemical reactions involve the breaking of old bonds and the formation of new ones, changing the substances involved into different substances. Each reaction can be described by a balanced chemical equation that represents the conservation of mass. This reflects the principle that matter is neither created nor destroyed in the reaction. For example, in the preparation of sodium chloride (NaCl), sodium (Na) and chlorine (Cl₂) react to form NaCl. Always, the same number of atoms present in the reactants is found in the products.

A sound understanding of these basics is crucial for grasping more intricate concepts like the law of conservation of mass and the law of definite composition.

law of definite composition

The law of definite composition states that a chemical compound always contains the same proportion of elements by mass. This means that no matter where a compound is obtained or how it is made, it will always have the same percentage of each element.

For example, consider sodium chloride (NaCl). In every sample of NaCl, the ratio of the mass of sodium (Na) to the mass of chlorine (Cl) will always remain consistent. This fixed ratio by mass is what defines the compound. A 100 g sample of NaCl will always contain approximately 39.34 g of Na and 60.66 g of Cl.

Let's apply this to our cases from the exercise:
- **Case 1**: 39.34 g of Na reacts with 60.66 g of Cl₂ to produce 100 g of NaCl. This perfectly follows the law of definite composition.
- **Case 2**: 39.34 g of Na reacts with 70 g of Cl₂. Even though we start with more chlorine than needed, the final product NaCl still has the same mass ratio. Here, the leftover chlorine confirms the fixed ratio.
- **Case 3**: 50 g of Na reacts with 50 g of Cl₂. In this scenario, there's an excess of sodium. After the reaction, NaCl forms with the same fixed ratio, leaving some unreacted sodium behind.
Understanding this consistency helps in predicting the outcome of chemical reactions and the amounts of each element needed.

chemical reactions

Chemical reactions are processes in which substances (reactants) transform into new substances (products) by breaking and forming chemical bonds. These reactions obey specific laws that ensure the reactions are predictable.

One such fundamental law is the law of conservation of mass, which states that the total mass of reactants must equal the total mass of products. This law can be observed in various cases:

• **Case 1**: The total mass of reactants, 39.34 g Na and 60.66 g Cl₂, equals the mass of the product, 100 g NaCl, illustrating the law of conservation of mass perfectly.
• **Case 2**: Here, 39.34 g Na reacts with 70 g Cl₂, forming 100 g NaCl and 9.34 g Cl₂ left over. The total mass remains 109.34 g on both sides of the reaction.
• **Case 3**: With 50 g of Na and 50 g of Cl₂ reacting, the products are 82.43 g NaCl and 17.57 g leftover Na, summing up to 100 g. Again, we see the conservation of mass maintained.

Different types of chemical reactions include synthesis, decomposition, single replacement, and double replacement. Each type involves different mechanisms and outcomes, but all abide by the conservation of mass and often the law of definite composition.
By understanding these laws and principles, we can predict and balance chemical reactions effectively, ensuring that they produce the desired substances accurately.