Question

Which of the following compounds are sparingly soluble in water (a) \(\mathrm{NH}_{4} \mathrm{Br}\) (b) \(\mathrm{AgBr}\) (c) \(\mathrm{KOH}\) (d) \(\mathrm{BaSO}_{4}\) ? How does this affect conductivity measurements?

Short answer

AgBr and BaSO₄ are sparingly soluble, leading to low conductivity.

Step-by-step solution

Understanding Solubility in Water

Sparingly soluble compounds dissolve very little in water. We can broadly characterize some compounds as either soluble or sparingly soluble using solubility rules. Compounds of alkali metals and ammonium are generally soluble. Hydroxides of alkali metals are also highly soluble. Silver halides and barium sulfate are typically sparingly soluble.

Analyzing Compound (a) - NH₄Br

Ammonium compounds like NH₄Br are soluble in water. Therefore, NH₄Br is not sparingly soluble.

Analyzing Compound (b) - AgBr

Silver salts, like AgBr, are often sparingly soluble in water due to the low solubility of silver halides.

Analyzing Compound (c) - KOH

KOH is a strong base and is highly soluble in water, making it easily dissolve to form an aqueous solution.

Analyzing Compound (d) - BaSO₄

Barium sulfate, BaSO₄, is a salt that is typically sparingly soluble in water, meaning it dissolves very little.

Effect on Conductivity Measurements

Sparingly soluble compounds, like AgBr and BaSO₄, dissolve partially, leading to low ion concentration in water. This results in poor conductivity compared to solutions with highly soluble compounds.

Key concepts

Sparingly Soluble Compounds

Sparingly soluble compounds are substances that only dissolve to a small extent in water. This means they release very few ions into the solution, affecting how they behave in a solution.
In simpler terms, while some compounds dissolve completely and vanish in water, sparingly soluble ones seem almost like they're staying solid.
For instance, if you drop a spoon of sugar in water, it disappears; however, if you drop a bit of chalk, it doesn't dissolve much. That's the essence of sparingly soluble.
Common examples include:

• Silver halides like silver bromide (AgBr)
• Barium sulfate (BaSO₄)

These compounds struggle to break into ions in water, limiting their solubility.
Understanding which compounds are sparingly soluble can help predict how they will react in various conditions, including their role in electrical conductivity.

Conductivity Measurements

Conductivity measurements are important in chemistry, as they tell us how well a solution can carry an electric current.
This ability to carry electrical charge depends on the availability of ions in the solution. When a substance dissolves in water, it releases ions, which are charged particles. These ions move freely and carry electricity.
However, with sparingly soluble compounds, like AgBr and BaSO₄, few ions are released into the water.

• This results in lower conductivity because fewer charged particles are available to move and carry an electric charge.
• In contrast, compounds that are highly soluble, like KOH, disband many ions, leading to high conductivity measurements.

Understanding conductivity is crucial in fields like electrochemistry, where precise measurements can determine a solution's properties.

Water Solubility Rules

Water solubility rules are guidelines used to predict the solubility of various compounds in water.
These rules are essential for determining which substances will dissolve in water and to what extent.
Here are some simple rules to follow:

• Most alkali metal compounds, such as sodium or potassium salts, are soluble in water.
• Ammonium compounds, like NH₄Br, are generally soluble.
• Hydroxides of alkali metals are highly soluble. However, most other metal hydroxides are sparingly soluble.
• Silver halides, except for silver fluoride, are typically not soluble in water.
• Sulfates are generally soluble, except for lead, barium, and calcium sulfates.

By applying these rules, predicting whether a compound will dissolve in water becomes easier. This knowledge aids not only in solving chemistry problems but also in practical applications, such as formulating solutions for industrial processes.