Question

Which of the following statement is falsc? (1) The solubility of gypsum in water increases with increase in temperature. (2) The solubility of gypsum in water increases in the presence of ammonium sulphate due to formation of a double salt. (3) Gypsum on heating to \(120^{\circ} \mathrm{C}\). forms plaster of paris. (4) Gypsum when heated to \(200^{\circ} \mathrm{C}\) ' converts into dead burnt.

Short answer

Statement 1 is false.

Step-by-step solution

Understanding the statements

Analyze each statement to determine its accuracy.

Analyze statement 1

The solubility of gypsum (CaSO4·2H2O) actually decreases with an increase in temperature due to its inverse solubility properties. Therefore, statement 1 is false.

Analyze statement 2

The solubility of gypsum does increase in the presence of ammonium sulfate as they form a double salt. Therefore, statement 2 is true.

Analyze statement 3

When gypsum is heated to around 120°C, it loses water and forms plaster of Paris (CaSO4·0.5H2O). Thus, statement 3 is true.

Analyze statement 4

Gypsum on heating to 200°C dehydrates further to form anhydrous calcium sulfate (CaSO4), known as dead burnt plaster. Hence, statement 4 is true.

Key concepts

inverse solubility

Gypsum (CaSO4·2H2O) has an interesting property called inverse solubility. In most cases, substances dissolve better in water as the temperature increases. However, gypsum does the opposite. Its solubility decreases as temperature rises. This means that at higher temperatures, less gypsum can be dissolved in water. This unique behavior is essential to understand because it affects how we handle and use gypsum in various processes. For instance, in industrial settings where temperature control is critical, knowing about inverse solubility can help in making better decisions.

So, remember, the next time you think about solubility, it's not always straightforward—gypsum is a perfect example of this fascinating twist.

ammonium sulfate

Ammonium sulfate ((NH4)2SO4) is a compound used in agriculture and industries for various purposes. One interesting fact about ammonium sulfate is its interaction with gypsum. When mixed with gypsum in water, the solubility of gypsum increases. This happens because ammonium sulfate helps form a double salt with gypsum, which is more soluble than gypsum alone. This property can be particularly useful in situations where we need to dissolve more gypsum in a solution.

For example, in soil treatment, where enhancing the calcium sulfate content is required, adding ammonium sulfate could be a practical solution. So, while working with gypsum and ammonium sulfate, remember this helpful interaction!

plaster of Paris formation

Plaster of Paris is a widely used material in construction, art, and medicine. It is formed by heating gypsum to around 120°C. When gypsum (CaSO4·2H2O) is heated, it loses part of its water and converts to Plaster of Paris (CaSO4·0.5H2O). This process is known as calcination. The heat-driven dehydration is partial, which is why the resulting compound still has some water content.

Plaster of Paris has a unique property where, upon mixing with water, it hardens and forms a solid structure. This makes it highly useful for making casts, molds, and even sculptures. Understanding the formation process helps in appreciating its versatile applications and its role in various industries.

dehydration of gypsum

Gypsum undergoes dehydration when heated to higher temperatures. At around 120°C, it forms Plaster of Paris, but if you increase the temperature to about 200°C, gypsum dehydrates completely to form what is known as dead burnt plaster. The chemical structure changes from CaSO4·2H2O to anhydrous CaSO4.

This anhydrous form is entirely void of water and is much different in properties compared to Plaster of Paris. It's more stable and doesn't react with water easily anymore, making it less useful for applications where reactivity with water is essential, like mold making or casts. Knowing the differences in these forms helps in choosing the right type of material for specific applications.