Acids are often used to remove rust and other corrosion from metals in a process known as pickling. They may be used as an electrolytes in a wet cell battery, such as sulfuric acid in car battery.

Introduction:
To remove acidity from solids, various methods can be employed. Acidity in solids can be caused by the presence of acidic compounds or by the formation of acid salts. These acidic properties can be undesirable in certain applications, such as in the food and pharmaceutical industries, where acidity can affect the taste, stability, and safety of the products. Therefore, it becomes important to neutralize or remove the acidity from solids.

Methods to remove acidity from solids:

1. Alkali Treatment:
- Alkali treatment is a common method used to remove acidity from solids.
- Alkalis, such as sodium hydroxide (NaOH) or potassium hydroxide (KOH), are added to the acidic solid to neutralize the acid.
- The alkali reacts with the acid to form water and a salt, which is usually non-acidic.
- The resulting salt can be easily separated from the solid, thereby removing the acidity.

2. Calcium Carbonate (CaCO3) Addition:
- Calcium carbonate can be added to acidic solids to neutralize the acidity.
- The carbonate ions in calcium carbonate react with the hydrogen ions present in the acid, forming water and carbon dioxide gas.
- This reaction results in the reduction of acidity in the solid.
- The excess carbon dioxide gas can be easily removed by purging or venting.

3. Buffering Agents:
- Buffering agents can be used to control and remove acidity from solids.
- Buffering agents are substances that resist changes in pH when acids or bases are added.
- They maintain the pH of the system within a certain range, preventing excessive acidity.
- Common buffering agents include sodium bicarbonate (NaHCO3) and sodium phosphate (Na3PO4).

4. Washing or Leaching:
- Washing or leaching the solid with water or a suitable solvent can remove acidic compounds from the surface.
- The solvent dissolves the acidic compounds, allowing them to be washed away.
- This method is particularly useful when the acidity is caused by surface contaminants or soluble acidic compounds.

5. Heat Treatment:
- Heat treatment can be employed to remove acidity from certain solids.
- Heating the solid at a specific temperature can cause the acid to volatilize or decompose, effectively removing the acidity.
- This method is commonly used in the purification of certain chemicals or pharmaceuticals.

Conclusion:
Removing acidity from solids is essential in various industries to ensure product quality, stability, and safety. Alkali treatment, calcium carbonate addition, buffering agents, washing or leaching, and heat treatment are some of the methods used to remove acidity. The choice of method depends on the specific requirements and properties of the solid being treated.