Question

The following compounds have been arranged in the increasing solubilities. Identify the correct order. 1\. \(\mathrm{Be}(\mathrm{OH})_{2}\) 2\. \(\mathrm{Mg}(\mathrm{OH})_{2}\) 3\. \(\mathrm{Ca}(\mathrm{OH})_{2}\) 4\. \(\mathrm{Sr}(\mathrm{OH})_{2}\) 5\. \(\mathrm{Ba}(\mathrm{OH})_{2}\)

Short answer

\( \mathrm{Be(OH)_2} < \mathrm{Mg(OH)_2} < \mathrm{Ca(OH)_2} < \mathrm{Sr(OH)_2} < \mathrm{Ba(OH)_2} \).

Step-by-step solution

Understand Solubility Trends in the Periodic Table

The solubility of hydroxides increases as we move down Group 2 of the periodic table. Therefore, we expect the alkaline earth metal hydroxides to become more soluble from beryllium to barium.

Arranging the Compounds

Based on the trend, the solubility order increases from beryllium hydroxide to barium hydroxide. So, the correct order from least to most soluble is: \( \mathrm{Be(OH)_2} < \mathrm{Mg(OH)_2} < \mathrm{Ca(OH)_2} < \mathrm{Sr(OH)_2} < \mathrm{Ba(OH)_2} \).

Verify with Known Data

Check if this order is consistent with known solubility data: Beryllium hydroxide and magnesium hydroxide are sparingly soluble; calcium hydroxide is moderately soluble, while strontium hydroxide and barium hydroxide are highly soluble. This verification confirms the order.

Key concepts

Group 2 Elements

Group 2 elements are a fascinating set of elements on the periodic table known as the alkaline earth metals. These elements include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). They are all located in the second column of the periodic table and share some common characteristics due to their position.
A key feature of Group 2 elements is their two valence electrons, which they can easily lose. This makes them highly reactive, though not as much as Group 1 elements. Their reactivity increases as you move down the group. Some basic properties that these elements share include:
- Shiny and silvery-white appearance. - Relatively low density compared to transition metals. - High melting points, though lower than Group 1 metals. The reactivity and properties of these elements play significant roles in many chemical phenomena, including the solubility trends observed with their hydroxides.

Alkaline Earth Metals

The alkaline earth metals, which correlate directly with Group 2 elements, are recognized not only for their physical characteristics but also for their chemical behaviors. These elements form oxides and hydroxides which are important in various chemical industries.
In particular, their hydroxides exhibit increasing basicity and solubility as we move down the group. For example, beryllium hydroxide (bOH_2) is largely insoluble in water, while barium hydroxide (Ba(OH)_2) is very soluble, forming a strong base in solution. Some key uses and reactions of alkaline earth metals include:
- Act as reducing agents and are often used to extract other metals from their compounds. - Calcium compounds are crucial in building materials such as cement and plaster. - Strontium and barium salts are utilized in fireworks for bright red and green colors respectively. Understanding these elements enhances our comprehension of not just chemical reactions but also their practical applications in daily life.

Hydroxides

Hydroxides are compounds that contain the hydroxide ion, OH^-. They are known for their basic properties and are formed when alkaline earth metals react with water. Each hydroxide's solubility in water can vary significantly, especially among different Group 2 metals.
One of the fascinating aspects of Group 2 hydroxides is their trend of increasing solubility from beryllium to barium. This can be attributed to the increasing basic character and the size of the metal cations as you move down the group. Here's a quick look at Group 2 hydroxides' solubility pattern:
- bOH_2 is almost insoluble. - Mg(OH)_2 is sparingly soluble. - Ca(OH)_2, also known as slaked lime, dissolves better but is still not highly soluble. - Sr(OH)_2 and Ba(OH)_2 are quite soluble, with barium hydroxide forming strong alkaline solutions. These differences play a vital role both in laboratory settings for predicting reactions and in industries where these compounds find various uses.