Question

Given below are a few electrolytes, indicate which one among them will bring about the coagulation of a gold sol quickest and in the least of concentration? (a) \(\mathrm{NaCl}\) (b) \(\mathrm{MgSO}_{4}\) (C) \(\mathrm{Nl}_{2}\left(\mathrm{SO}_{4}\right)_{3}\) (d) \(\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\)

Short answer

\(\text{{Al}}_2(\text{{SO}}_4)_3\) will bring about the quickest coagulation in the least concentration due to its trivalent cations.

Step-by-step solution

Understanding Coagulation

Coagulation of sols is primarily governed by the Hardy-Schulze rule, which states that the greater the valence of the oppositely charged ion of the electrolyte, the greater is its power to cause coagulation. For coagulating negatively charged gold sols, cations are effective.

Analyzing the Cations of the Given Electrolytes

Identify the cations in each compound: (a) \(\text{{Na}}^+\text{{ from NaCl}}\), (b) \(\text{{Mg}}^{2+}\text{{ from MgSO}}_4\), (c) \(\text{{Al}}^{3+}\text{{ from Al}}_2(\text{{SO}}_4)_3\), and (d) \(\text{{K}}^+\text{{ from K}}_4[\text{{Fe}}(\text{{CN}})_6]\). Their charges are +1, +2, +3, and +1 respectively.

Applying the Hardy-Schulze Rule

According to the Hardy-Schulze rule, the electrolyte with the cation of highest valency will be the most effective coagulant. Among the given electrolytes, \(\text{{Al}}^{3+}\) from \(\text{{Al}}_2(\text{{SO}}_4)_3\) has the highest valency of +3.

Determining the Most Effective Coagulant

Therefore, \(\text{{Al}}_2(\text{{SO}}_4)_3\) will bring about coagulation of the gold sol fastest and in the least concentration since it has the highest valency cation among the options.

Key concepts

Hardy-Schulze Rule

The Hardy-Schulze rule is a fundamental principle in colloid chemistry that helps us understand how the coagulation, or clumping together, of colloid particles occurs. In its essence, this rule states that the higher the charge (or valency) of an ion opposite in charge to the colloidal particles, the more effective it will be at causing the sol to coagulate. This is crucial when considering how to purify water, process minerals, or in certain medical applications.

For example, imagine a gold sol with negatively charged particles. To coagulate this sol, you would add a positively charged electrolyte. According to the Hardy-Schulze rule, if this electrolyte's cation has a higher charge, it will not only cause coagulation more efficiently but also require a lower concentration to achieve it. This principle has significant practical applications, as it allows for more efficient and cost-effective processes in various industries.

Electrolytes in Coagulation

When dealing with the coagulation of sols, electrolytes play a pivotal role. An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent like water. The ions from the electrolyte promote the coagulation by reducing the charges on the colloidal particles, allowing them to come closer together and form larger aggregates.

Role of Cations and Anions

In the context of a negatively charged gold sol, it's the positively charged ions, or cations, that are of interest. These cations neutralize the charge of the gold particles, which leads to the aggregation of the particles, eventually causing the sol to coagulate. This applies to various types of sols and is an essential concept in both industrial applications and laboratory practices. The efficiency of this process strongly depends on the type and concentration of the ions present in the solution.

Valency and Coagulation

The concept of valency is integral to the coagulation process of sols, especially when applying the Hardy-Schulze rule. Valency, in simple terms, refers to the combining power of an element, often indicated by the number of hydrogen atoms that can combine with or displace to form compounds. In the context of coagulation, the valency of the ion relates to its charge, which directly impacts its ability to neutralize the colloid particles and bring about coagulation.

Higher Valency Means More Effective Coagulation

The higher the valency of the ion, the stronger its power to coagulate the sol. This is because ions with higher charges can neutralize more oppositely charged colloidal particles, leading to a faster and more effective coagulation. Thus, in comparing different coagulating agents, one usually looks for the agent with ions of higher valency, as they will work in lower concentrations and achieve coagulation more swiftly, which is beneficial both economically and operationally.