Problem 70 - Chemistry: The Central Science

Question

Write a balanced equation for the reaction that occurs in each of the following cases: (a) Cesium is added to water. (b) Strontium is added to water. (c) Sodium reacts with oxygen. (d) Calcium reacts with iodine.

Step-by-Step Solution

Answer

(a) \(2Cs + 2H_2O \rightarrow 2CsOH + H_2\) (b) \(Sr + 2H_2O \rightarrow Sr(OH)_2 + H_2\) (c) \(4Na + O_2 \rightarrow 2Na_2O\) (d) \(Ca + I_2 \rightarrow CaI_2\)

Step 1: (a) Cesium is added to water.

Cesium (Cs) is an alkali metal that reacts with water (H₂O) to form cesium hydroxide (CsOH) and hydrogen gas (H₂). The unbalanced equation for this reaction is: Cs + H₂O -> CsOH + H₂ To balance the equation, we simply need to adjust the coefficients: 2Cs + 2H₂O -> 2CsOH + H₂

Step 2: (b) Strontium is added to water.

Strontium (Sr) is an alkaline earth metal that reacts with water (H₂O) to form strontium hydroxide (Sr(OH)₂) and hydrogen gas (H₂). The unbalanced equation for this reaction is: Sr + H₂O -> Sr(OH)₂ + H₂ To balance the equation, we simply need to adjust the coefficients: Sr + 2H₂O -> Sr(OH)₂ + H₂

Step 3: (c) Sodium reacts with oxygen.

Sodium (Na) is an alkali metal that reacts with oxygen (O₂) to form sodium oxide (Na₂O). The unbalanced equation for this reaction is: Na + O₂ -> Na₂O To balance the equation, we need to adjust the coefficients: 4Na + O₂ -> 2Na₂O

Step 4: (d) Calcium reacts with iodine.

Calcium (Ca) is an alkaline earth metal that reacts with iodine (I₂) to form calcium iodide (CaI₂). The unbalanced equation for this reaction is: Ca + I₂ -> CaI₂ To balance the equation, we simply need to adjust the coefficients: Ca + I₂ -> CaI₂ The balanced chemical equations for each reaction are as follows: (a) 2Cs + 2H₂O -> 2CsOH + H₂ (b) Sr + 2H₂O -> Sr(OH)₂ + H₂ (c) 4Na + O₂ -> 2Na₂O (d) Ca + I₂ -> CaI₂

Key Concepts

Balancing Chemical Equations

Balancing chemical equations is a fundamental skill in chemistry. It ensures that the mass and the number of atoms are equal on both sides of a chemical reaction. The principle behind balancing equations is the conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction.

• To balance an equation, start by writing the unbalanced equation with all reactants on the left and products on the right.
• Use coefficients to multiply the number of molecules of each substance until the number of each type of atom is the same on both sides.
• Balanced equations allow chemists to accurately predict the amounts of products that will form from given reactants.

As an example, when balancing the equation for the reaction of cesium with water, the initial unbalanced equation is Cs + H₂O -> CsOH + H₂. By adjusting the coefficients to 2 Cs + 2 H₂O on the left, we ensure that they balance with 2 CsOH + H₂ on the right, conserving mass and atoms.

Alkali Metals

Alkali metals are located in Group 1 of the periodic table. This group includes elements like sodium (Na), potassium (K), and cesium (Cs). These metals are highly reactive, especially with water and oxygen.

• Their reactivity increases as you move down the group in the periodic table.
• They have a single electron in their outermost shell, making them eager to lose that electron in reactions.
• Often these reactions are vigorous and even explosive. For instance, when cesium is added to water, it reacts to form cesium hydroxide and hydrogen gas, as shown in the balanced equation: 2 Cs + 2 H₂O -> 2 CsOH + H₂.

Understanding the behavior of alkaline metals helps in predicting their reactions with other elements, which is a crucial part of chemistry.

Alkaline Earth Metals

Alkaline earth metals are found in Group 2 of the periodic table. This category includes elements like magnesium (Mg), calcium (Ca), and strontium (Sr). These metals are also reactive, but less so than alkali metals.

• They typically form +2 ions because they have two electrons in their outer shell that they tend to lose in reactions.
• These metals react with water, albeit less violently than alkali metals, forming hydroxides and releasing hydrogen gas.
• An example of this is strontium reacting with water, forming strontium hydroxide: Sr + 2 H₂O -> Sr(OH)₂ + H₂.

Alkaline earth metals are essential in various industries and have important applications due to their unique properties and reactivity.