Question

A 10.0-g sample of magnesium reacts with oxygen to form 16.6 g of magnesium oxide. How many grams of oxygen reacted?

Short answer

The mass of oxygen that reacted is found by applying the law of conservation of mass: mass of Mg + mass of O = mass of MgO. Plugging in the given values, we have mass of O = 16.6 g - 10.0 g, resulting in a mass of oxygen of 6.6 g.

Step-by-step solution

1. Identify the given information.

We are given: - Mass of magnesium (Mg) = 10.0 g - Mass of magnesium oxide (MgO) = 16.6 g Our goal is to find the mass of oxygen (O)

2. Apply the law of conservation of mass.

According to the law of conservation of mass, the total mass of the reactants equals the total mass of the products. In this case, the reactants are magnesium (Mg) and oxygen (O), while the product is magnesium oxide (MgO). So, mass of Mg + mass of O = mass of MgO

3. Solve for the mass of oxygen.

We can now plug in the given values and solve for the mass of oxygen: Mass of O = mass of MgO - mass of Mg Mass of O = 16.6 g - 10.0 g

4. Calculate the mass of oxygen.

Perform the calculation to obtain the mass of oxygen: Mass of O = 6.6 g So, 6.6 grams of oxygen reacted with magnesium to form magnesium oxide.

Key concepts

Chemical Reactions

Chemical reactions involve the transformation of one or more substances into new products. In our example with magnesium and oxygen, the chemical reaction forms magnesium oxide. Here is how the process typically works:
- **Reactants:** These are the starting materials. In this scenario, magnesium (Mg) and oxygen (O₂) are the reactants.
- **Products:** These are the substances formed as a result of the chemical reaction. Here, the product is magnesium oxide (MgO).
- **Reaction Process:** The atoms in the reactants are reorganized to form new chemical bonds, resulting in the product. It's important to note that the type and number of atoms remain the same, preserving mass consistency according to the **law of conservation of mass**. In chemical equations, each element's conservation is demonstrated through a balanced equation. For example, for the formation of magnesium oxide: $$2\text{Mg}+{\text{O}}_2\to 2\text{MgO}$$ This illustrates that two magnesium atoms react with a molecule of oxygen to produce two formula units of magnesium oxide.

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions. It completely relies on the law of conservation of mass and involves using balanced chemical equations. In our example reaction, stoichiometry helps us understand how much of each reactant is needed. **Key Concepts of Stoichiometry:**
- **Mole Ratios:** From the balanced equation, the ratio reveals the proportion of reactants to products. In our magnesium oxide example, two moles of Mg react with one mole of O₂ to produce two moles of MgO.
- **Cross-relationships:** Stoichiometry allows us to calculate related quantities like masses, moles, and molecules, based on the known mass of one substance.
- **Limiting Reagents:** It identifies the reactant that is used up first, dictating the amount of product formed. In our example, if given a limited amount of either Mg or O₂, stoichiometry helps to find out which one runs out first. To master stoichiometry, start with a balanced chemical equation, use the mole ratios as conversion factors, and apply them to calculate necessary quantities.

Mass Calculation

Mass calculation in chemistry is rooted in the **law of conservation of mass**, which states that mass in a closed system must remain constant over time. This means total mass of reactants equals the total mass of products in a chemical reaction. Consider how this principle was applied to calculate the mass of oxygen in our example:1. **Identify Given Masses:** We know the mass of magnesium (10.0 g) and the mass of magnesium oxide (16.6 g).
2. **Apply the Law:** Using the formula: $$\text{mass of Mg}+\text{mass of O}=\text{mass of MgO}$$we rearrange to solve for the unknown mass of oxygen: $$\text{mass of O}=16.6\text{ g}-10.0\text{ g}$$ 3. **Perform Calculation:** This gives us a mass of 6.6 g for oxygen, confirming the mass of oxygen that reacted.Understanding mass calculations is key in chemistry as it helps verify how reactants convert into products quantitatively, assuring no mass is lost in the reaction.