Question

Which one of the following processes will produce hard water? (a) saturation of water with \(\mathrm{CaCO}_{3}\) (b) addition of \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) to water (c) saturation of water with \(\mathrm{MgCO}_{3}\) (d) saturation of water with \(\mathrm{CaSO}_{4}\)

Short answer

Saturation of water with \(\mathrm{CaSO}_{4}\) (option d) produces hard water.

Step-by-step solution

Understanding Hard Water

Hard water contains high concentrations of calcium (Ca) or magnesium (Mg) ions. These ions typically come from soluble compounds like calcium sulfate (\(\mathrm{CaSO}_4\)), calcium carbonate (\(\mathrm{CaCO}_3\)), magnesium carbonate (\(\mathrm{MgCO}_3\)), and magnesium sulfate (\(\mathrm{MgSO}_4\)). When water is saturated with these compounds, it can become hard.

Analyzing Option (a)

Option (a) involves saturating water with \(\mathrm{CaCO}_3\). Although calcium carbonate can cause water hardness, it is minimally soluble in water, which means it does not significantly increase the calcium ion concentration in water. Thus, it is unlikely to contribute to water hardness through saturation.

Analyzing Option (b)

Option (b) suggests adding \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) to water. Sodium sulfate does not add any calcium or magnesium ions to water, so it will not make the water hard. Instead, it only increases the concentration of sodium and sulfate ions.

Analyzing Option (c)

Option (c) involves saturating water with \(\mathrm{MgCO}_3\). This compound involves magnesium, and since it can dissolve to some extent in water, it releases \(\mathrm{Mg}^{2+}\) ions. The presence of these ions may contribute to the hardness of the water.

Analyzing Option (d)

Option (d) involves saturating water with \(\mathrm{CaSO}_{4}\). Calcium sulfate is more soluble than calcium carbonate, leading to the presence of \(\mathrm{Ca}^{2+}\) ions in water. The addition of calcium ions is a direct cause of hard water.

Conclusion: Identifying the Process Leading to Hard Water

Based on the analysis, both options (c) and (d) introduce ions known to cause hardness. However, since the prompt asks for "which one," the more straightforward and common contributor would be option (d), \(\mathrm{CaSO}_4\), due to its higher solubility.

Key concepts

Calcium Ions

Calcium ions, denoted as \(\text{Ca}^{2+}\), play a pivotal role in the formation of hard water. When water comes in contact with calcium-containing minerals, such as calcium sulfate \(\text{CaSO}_4\) or calcium carbonate \(\text{CaCO}_3\), these minerals can dissolve and release \(\text{Ca}^{2+}\) ions into the water. When the concentration of \(\text{Ca}^{2+}\) ions in water increases, the water becomes 'hard'.

Hard water doesn't easily create a lather with soap, making washing tasks more challenging. This is because calcium ions react with the soap, forming a precipitate called soap scum instead of luscious bubbles.

Important to understand is that while \(\text{CaCO}_3\) can introduce calcium ions, it is less soluble in water compared to \(\text{CaSO}_4\). This makes \(\text{CaSO}_4\) a more significant contributor to hard water due to its ability to readily release more \(\text{Ca}^{2+}\) ions.

• Calcium ions cause water hardness.
• \(\text{CaSO}_4\) is more soluble and thus contributes more to water hardness than \(\text{CaCO}_3\).
• Presence of \(\text{Ca}^{2+}\) reduces the efficiency of soap's cleaning action.

Magnesium Ions

Magnesium ions, represented as \(\text{Mg}^{2+}\), are another key factor contributing to water hardness. Similar to calcium ions, when water interacts with minerals such as magnesium carbonate \(\text{MgCO}_3\) or magnesium sulfate \(\text{MgSO}_4\), magnesium ions may dissolve into the water.

The presence of \(\text{Mg}^{2+}\) ions in water can cause similar effects as calcium ions, such as reduced soap lathering efficiency and the formation of deposits in pipes and appliances. Even if a compound like \(\text{MgCO}_3\) has limited solubility, it can still contribute to making water hard by releasing these ions.

Understanding magnesium's role is vital for regions where these minerals are prevalent in groundwater. Recognizing which minerals are more soluble helps in determining the hardness potential of a water source.

• Magnesium ions also cause water hardness.
• \(\text{MgCO}_3\) and \(\text{MgSO}_4\) are common sources of \(\text{Mg}^{2+}\).
• Hard water impacts lathering and can lead to pipe scaling.

Water Hardness

Water hardness is defined by the concentration of dissolved calcium (\(\text{Ca}^{2+}\)) and magnesium (\(\text{Mg}^{2+}\)) ions in the water. When people say water is 'hard', it means there's a high mineral content, especially these ions. Hard water is usually formed when water passes through or remains in contact with geological formations of calcium and magnesium-rich stones or soil.

Hard water has several noticeable effects. It may leave scale deposits in appliances, reducing their efficiency and lifespan. Also, it requires more soap or detergent to achieve cleaning since the ions interfere with soap's ability to lather effectively.

Testing water hardness is important for various household and industrial applications, where water softer options might be considered if high levels of hardness are found. Water hardness is a common issue with straightforward solutions like ion exchange systems or simply switching to softened water sources.

• High \(\text{Ca}^{2+}\) and \(\text{Mg}^{2+}\) indicate hard water.
• Caused by contact with mineral-rich areas.
• Leads to soap inefficiency and scaling in appliances.