Problem 82 - General Chemistry

Question

Associate each of the solids \(\mathrm{BN}, \mathrm{P}_{4} \mathrm{~S}_{3}, \mathrm{~Pb}\), and \(\mathrm{CaCl}_{2}\) with one of the following sets of properties. a. A bluish white, lustrous solid melting at \(327^{\circ} \mathrm{C}\); the solid is soft and malleable. b. A white solid melting at \(772^{\circ} \mathrm{C}\); the solid is an electrical nonconductor but dissolves in water to give a conducting solution. C. A yellowish green solid melting at \(172^{\circ} \mathrm{C}\). d. A very hard, colorless substance melting at about \(3000^{\circ} \mathrm{C}\).

Step-by-Step Solution

Answer

BN matches (d), \(\text{P}_4\text{S}_3\) matches (c), Pb matches (a), \(\text{CaCl}_2\) matches (b).

Step 1: Understanding Each Compound's Characteristics

First, we will consider the chemical compositions and typical characteristics. \[\text{BN} \] is boron nitride and typically forms a very hard, colorless solid. \[\text{P}_4\text{S}_3\] is a phosphorus trisulfide, often seen as a yellowish solid. \[\text{Pb}\] stands for lead, a soft, malleable metal with a lustrous bluish white appearance. \[\text{CaCl}_2\] is calcium chloride, a soluble white solid.

Step 2: Matching Properties with Compounds

Now, associate the given compounds with the properties described.- "A bluish white, lustrous solid" as described in \(\text{(a)}\) matches \(\text{Pb}\) because lead is a soft, malleable metal, with a melting point of \(327^{\circ} \mathrm{C}\).- "A white solid melting at \(772^{\circ} \mathrm{C}\)" in \(\text{(b)}\) aligns with \(\text{CaCl}_2\), which is an ionic compound and conducts electricity when dissolved in water.- "A yellowish green solid melting at \(172^{\circ} \mathrm{C}\)" described in \(\text{(c)}\) matches \(\text{P}_4\text{S}_3\), known for its yellowish appearance.- "A very hard, colorless substance melting at about \(3000^{\circ} \mathrm{C}\)" from \(\text{(d)}\) corresponds to \(\text{BN}\), as it is similar to diamond in hardness.

Key Concepts

Boron Nitride

Boron nitride, or BN, is a fascinating compound with remarkable properties. It exists in several forms, with the most common being hexagonal boron nitride (h-BN), which is analogous to graphite. However, its cubic form, similar to diamond, is incredibly hard and is often used in cutting tools and abrasives. This compound is colorless and can withstand high temperatures, with a melting point around 3000°C. This robust nature makes boron nitride an important material in industries that require materials capable of enduring extreme conditions. Particularly its resistance to wear and chemical attack is highly prized.
Moreover, boron nitride's thermal and chemical stability is complemented by its electrical insulating properties. This makes it useful in electronics, often serving as a substrate that can withstand and dissipate heat from computing components efficiently. Although BN is an electrical nonconductor, it can be combined with other materials to expand its application scope.

• High thermal stability
• Extreme hardness in cubic form
• Electrical insulation

Phosphorus Trisulfide

Phosphorus trisulfide, with the molecular formula \( \text{P}_4\text{S}_3 \), is known for its distinctive yellowish-green appearance. It is primarily used in the production of safety matches due to its ability to ignite when struck. This chemical property stems from its relatively low melting point of 172°C, which allows it to vaporize and subsequently react quickly, producing flames.
As an important industrial chemical, phosphorus trisulfide must be handled with care due to its reactive nature. It poses some hazards if not managed properly, particularly because it can release toxic gases upon decomposition. Hence, it requires careful storage and handling procedures in controlled environments to ensure safety during its use.

• Yellowish-green color
• Melting point at 172°C
• Use in safety match production

Lead

Lead, symbolized as \( \text{Pb} \), is a well-known metal due to its bluish-white luster and highly malleable nature. With a relatively low melting point of 327°C, it can easily be cast into various shapes. Historically, lead has been used extensively in plumbing, paint, and batteries due to its versatility.
Despite its useful properties, lead is toxic and can cause significant health issues if ingested or inhaled. As a result, modern regulations have drastically reduced its use in products that might pose a risk to human health. Nonetheless, lead's ability to absorb radiation makes it invaluable in protective shielding in medical and nuclear settings.

• Bluish-white luster
• Malleability and softness
• Radiation shielding

Calcium Chloride

Calcium chloride, represented by \( \text{CaCl}_2 \), is a white solid that is widely known for its high solubility in water and ability to dissociate into ions, which allows it to conduct electricity in solution. It melts at 772°C, making it suitable for applications requiring moderate thermal stability.
Generally, calcium chloride's role in industry is vast, including use as a de-icing agent on roads and pavements due to its effective ice-melting properties at lower temperatures than sodium chloride. It is also utilized in controlling dust, as a desiccant to maintain dry conditions in sealed containers, and even in food preparation as a firming agent.

• High solubility in water
• Melting point at 772°C
• Used as a de-icing agent