Question

Which of the following is the best scientific method to test presence of water in a liquid? (a) Taste (b) Smell (c) Use of litmus paper (d) Use of anhydrous copper sulphate.

Short answer

The best method is to use anhydrous copper sulphate (option d).

Step-by-step solution

Understanding the Options

First, let's understand what each method involves. Tasting involves using taste buds to identify water, which is not reliable or safe for unidentified liquids. Smelling involves using your nose, but many liquids, including water, are odorless. Using litmus paper checks for acidity or basicity, which does not directly test for water. Anhydrous copper sulfate reacts with water to form hydrated copper sulfate, changing its color, making it a specific test for water.

Eliminating Inappropriate Methods

Since tasting an unidentified liquid can be harmful, option (a) is not a safe or reliable method. Option (b), smelling, is also not effective as many liquids do not have a characteristic smell indicating the presence of water.

Testing with Litmus Paper

Litmus paper changes color in acidic or basic solutions, but water itself is neutral and typically does not affect litmus paper unless it contains dissolved substances. Thus, litmus paper is not the best way to test for water, eliminating option (c).

Using Anhydrous Copper Sulphate

Anhydrous copper sulfate is white, and upon contact with water, it reacts and forms hydrated copper sulfate, which is blue. This color change is a clear indication of the presence of water, making it a reliable test.

Conclusion

Considering all the options, using anhydrous copper sulfate is the most scientifically sound method for testing the presence of water, as it provides a clear visual indication of water through a color change.

Key concepts

Use of Anhydrous Copper Sulphate

Anhydrous copper sulphate is a white powder that acts as a precise tool in detecting water. It's a practical choice because this compound undergoes a distinct transformation upon exposure to water.
Anhydrous means without water, and in this state, copper sulphate appears white. When it comes into contact with water, it absorbs the moisture and transforms into hydrated copper sulphate, which is blue. This color change makes it easy to detect even small traces of water.
To use it as a test, simply add a small amount of anhydrous copper sulphate to the sample you suspect contains water. If the powder turns from white to blue, it confirms the presence of water.

• This method leverages a chemical reaction that is specific to water.
• No complex equipment or processes are needed, making it accessible for various settings.

This straightforward chemical indicator is reliable and visual, ensuring its place as a staple method for detecting water.

Chemical Indicators

Chemical indicators are substances that have a color change to signal the presence or concentration of a chemical substance. In the context of detecting water, these indicators play a crucial role.
One of the most famous chemical indicators for water is anhydrous copper sulphate, due to its ability to change color visibly when it becomes hydrated. This visual cue helps in affirming the outcomes of the tests.

• Chemical indicators are highly specific, meaning they tend to react with specific substances.
• Their simplicity and effectiveness make them a preferred choice in many practical scenarios.

Considering their ease of use and clarity in results, chemical indicators facilitate fast and reliable testing for substances like water, without the need for elaborate laboratory setups.

Water Detection Methods

Detecting the presence of water in various environments can be crucial, especially in scientific settings. Multiple methods may be employed, each with its own advantages and disadvantages.
Simple methods like tasting or smelling are unreliable and unsafe, especially when dealing with unknown liquids. Other techniques like using litmus paper focus on determining acidity or alkalinity, which are not direct indicators of water on its own.
The most effective method for water presence detection is using chemical methods, such as those involving anhydrous copper sulphate.

• This method offers a clear visual confirmation through a color change.
• It is easy to execute and reliable, providing results without advanced technical requirements.

Ultimately, the choice of method depends on the specific context and requirement for precision. However, using chemical reactions like those with anhydrous copper sulphate remains a scientifically sound option for conclusive results.