Question

A car owner who knows no chemistry has to put antifreeze in his car's radiator. The instructions recommend a mixture of \(30 \%\) ethylene glycol and \(70 \%\) water. Thinking he will improve his protection he uses pure ethylene glycol. He is saddened to find that the solution does not provide as much protection as he hoped. Why not?

Short answer

Using pure ethylene glycol instead of the recommended mixture of \(30\%\) ethylene glycol and \(70\%\) water is less effective because it has a higher viscosity, making it difficult for the coolant to circulate properly, leading to an inefficient cooling system and possible engine damage. Also, pure ethylene glycol has a higher boiling point than the mixture, making it less effective in preventing overheating in hot conditions. The recommended mixture provides the best balance of protection against freezing, overheating, and proper circulation of the coolant.

Step-by-step solution

Introduction to ethylene glycol

Ethylene glycol is the main component in many antifreeze solutions for car radiators. Its purpose is to lower the freezing point of the coolant to prevent the radiator and engine from freezing. It is also used to increase the boiling point of the coolant to prevent overheating in hot conditions.

Properties of ethylene glycol and water

Ethylene glycol by itself has a lower freezing point than water, which is why it is used as an antifreeze. However, when ethylene glycol is mixed with water, the freezing point of the mixture is even lower than that of pure ethylene glycol, providing better protection against freezing and better overall performance.

The importance of the mixture

The recommended mixture of \(30\%\) ethylene glycol and \(70\%\) water is based on the fact that this ratio provides the best balance of protection against both freezing and boiling. Too much ethylene glycol or too little water can negatively affect the properties of the antifreeze solution.

Why pure ethylene glycol is not as effective

When the car owner uses pure ethylene glycol instead of the recommended mixture, he might think that he is providing even better protection against freezing. However, that is not the case. Pure ethylene glycol has a higher viscosity, which makes it difficult for the coolant to circulate properly. This can lead to an inefficient cooling system, and in the worst case, it can cause overheating and damage to the engine. Furthermore, pure ethylene glycol has a higher boiling point than the mixture, which makes it less effective in preventing overheating in hot conditions. In summary, the car owner should follow the manufacturer's recommendation of a \(30 \%\) ethylene glycol and \(70 \%\) water mixture to achieve the best balance of protection against freezing, overheating, and proper circulation of the coolant. Using pure ethylene glycol can negatively affect the performance of the cooling system and potentially lead to damage to the engine.

Key concepts

Colligative Properties

Colligative properties are characteristics of solutions that depend solely on the number of dissolved particles and not on the type of particles.
These properties include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure. When it comes to solutions like antifreeze, understanding colligative properties can help us grasp why certain mixtures perform better than others.

For instance, the addition of ethylene glycol to water introduces more particles into the solution. Because the freezing point depression is a colligative property, the more particles present, the lower the freezing point will be. This principle explains why the radiator's mixture needs to be balanced: it ensures enough particles are present to effectively lower the freezing point, without compromising other key features such as fluidity.

Freezing Point Depression

Freezing point depression is one specific colligative property that's crucial for understanding how antifreeze works. It refers to the phenomenon where the freezing point of a liquid (solvent), such as water, is lowered by adding a solute, like ethylene glycol.

The extent of freezing point depression can be calculated using the formula:
\( \triangle T_f = i \times K_f \times m \tag{1} \)
where
\( \triangle T_f \) is the change in freezing point,
\( i \) is the van't Hoff factor (the number of particles the solute dissociates into),
\( K_f \) is the freezing point depression constant of the solvent, and
\( m \) is the molality of the solution.

Practical Application in Antifreeze

Not only does ethylene glycol lower the freezing point, but the optimum mixture also ensures proper heat transfer and prevents corrosion within the car's cooling system. The mixture lowers the freezing point more efficiently than pure ethylene glycol due to the combination of its physical properties and the effect of freezing point depression.

Solution Chemistry

Solution chemistry involves studying the properties and behaviors of solutions. Solutions are homogeneous mixtures of two or more substances: the solute(s) and the solvent. The solvent is the component of the solution that is present in a greater amount, and the solute is the substance dissolved in the solvent.

Specifically, in the context of antifreeze, water is the solvent and ethylene glycol is the solute. When mixed, these two form a solution that acts differently from either component on its own. Key characteristics such as solubility, the polarity of molecules, and intermolecular forces play significant roles in how substances interact within a solution.

Why Pure Ethylene Glycol Isn't Ideal

When we examine the solution of ethylene glycol and water, we find the interactions between the ethylene glycol molecules and water molecules result in lower viscosity and better antifreeze capabilities than pure ethylene glycol. This ideal mix also promotes optimal heat conduction and less strain on the vehicle's engine, ensuring that it runs efficiently in both cold and hot temperatures.