Magnesium is a valuable, light weight metal used as a structural material as well as in alloys, batteries, and in chemical synthesis. Although magnesium is plentiful in Earth's crust, it is mainly found in the sea water (after sodium). There is about 1.3 g of magnesium in every kilogram of sea water. The process for obtaining magnesium from sea water employs all three types of reactions, i.e., precipitation, acid-base, and redox-reactions.
Acid-base reaction involves reaction between :

Options

A. `MgCO_(3)` and HCl
B. `Mg(OH)_(2) and H_(2)SO_(4)`
C. `Mg(OH)_(2) and HCl`
D. `MgCO_(3) and H_(2)SO_(4)`

Answer

To solve the question regarding the acid-base reaction involved in the process of obtaining magnesium from seawater, we can break it down into the following steps:

### Step 1: Identify the components in seawater
Seawater contains various dissolved salts, including magnesium chloride (MgCl₂), which is the primary source of magnesium.

**Hint:** Look for the main compounds present in seawater that contain magnesium.

### Step 2: Understand the precipitation reaction
To extract magnesium from seawater, calcium hydroxide (Ca(OH)₂), also known as slaked lime, is added to the seawater. This leads to a precipitation reaction where magnesium hydroxide (Mg(OH)₂) is formed as a precipitate.

**Hint:** Recall that a precipitation reaction occurs when two soluble salts react to form an insoluble compound.

### Step 3: Write the precipitation reaction
The reaction can be represented as:
\[ \text{MgCl}_2 + \text{Ca(OH)}_2 \rightarrow \text{Mg(OH)}_2 \downarrow + \text{CaCl}_2 \]
Here, Mg(OH)₂ precipitates out of the solution.

**Hint:** Identify the products of the reaction and note which one is the precipitate.

### Step 4: Identify the acid-base reaction
The precipitated magnesium hydroxide (Mg(OH)₂) is then treated with hydrochloric acid (HCl). This is an acid-base reaction where magnesium hydroxide reacts with hydrochloric acid to form magnesium chloride and water.

**Hint:** Look for the neutralization reaction where a base reacts with an acid.

### Step 5: Write the acid-base reaction
The acid-base reaction can be represented as:
\[ \text{Mg(OH)}_2 + 2\text{HCl} \rightarrow \text{MgCl}_2 + 2\text{H}_2\text{O} \]

**Hint:** Remember that in an acid-base reaction, water is often produced along with a salt.

### Step 6: Conclusion
From the above steps, we conclude that the acid-base reaction involved in obtaining magnesium from seawater is between magnesium hydroxide (Mg(OH)₂) and hydrochloric acid (HCl).

**Final Answer:** The acid-base reaction involves magnesium hydroxide (Mg(OH)₂) and hydrochloric acid (HCl).