Sodium bicarbonate is a sodium salt of carbonic acid. It's called 'bicarbonate of sodium' or 'acid carbonate of sodium,' due to the presence of one sodium atom compared to two in regular sodium carbonate. Epsom salt is magnesium sulfate, while green vitriol and white vitriol are iron and zinc sulfates respectively. True alum is a double sulfate containing aluminum and potassium. Limestone, chalk, and marble are calcium carbonates.
When limestone (calcium carbonate) is heated in a limekiln, it decomposes into calcium oxide ('quicklime') and CO2 gas. Calcium oxide reacts with water to form calcium hydroxide, which is strongly alkaline. Carbon dioxide can react with calcium oxide or hydroxide to reform calcium carbonate.
Water (HOH), carbonic acid (HOOOH), and calcium hydroxide (HOCaOH) are composed of hydrogen, oxygen, and other elements in specific ratios. When sulfuric acid is added to calcium carbonate, it forms calcium sulfate, water, and CO2 gas. <Callout type="important" title="Key Reaction">Calcium Carbonate + Sulfuric Acid → Calcium Sulfate + Water + Carbon Dioxide</Callout>
Questions about the valence of elements are posed, with answers explaining hydrogen, oxygen, and other element valences. The chapter concludes by detailing atomic linking and variable valence.
Key Takeaways
- Sodium bicarbonate is a sodium salt of carbonic acid with unique properties compared to regular sodium carbonate.
- Epsom salt, green vitriol, and white vitriol are magnesium sulfate, iron sulfate, and zinc sulfate respectively.
- Limestone decomposes into quicklime and CO2 gas when heated.
Practical Tips
- Understand the chemical composition of common compounds like sodium bicarbonate for practical applications in cooking or medicine.
- Recognize that limestone can be transformed into lime through heating, a process used historically in construction.
Warnings & Risks
- Incorrect handling of quicklime (calcium oxide) can cause severe burns due to its caustic nature.
- Improper storage and use of sulfuric acid can lead to dangerous reactions with other substances.
Modern Application
While the chapter focuses on historical chemical processes, understanding these reactions is crucial for modern survival scenarios. Knowledge of how to transform limestone into lime or produce calcium carbonate from quicklime can be vital in emergency construction or purification tasks.
Frequently Asked Questions
Q: What happens when limestone is heated?
When limestone (calcium carbonate) is strongly heated, it decomposes into calcium oxide ('quicklime') and carbon dioxide gas.
Q: How does sulfuric acid react with calcium carbonate?
Sulfuric acid reacts with calcium carbonate to form calcium sulfate, water, and carbon dioxide gas. The reaction is: CaCO3 + (HO)2SO4 → CaSO4 + HOH + OCO.
Q: What are the valences of hydrogen and oxygen?
The valence of hydrogen is invariably 1, while that of oxygen in combination is invariably 2. This means one atom of oxygen can hold two hydrogen atoms directly to it.