Question

Suggest a way to determine if the colorless liquid in a beaker is water. How could you discover if there is salt dissolved in the water?

Short answer

Boil the liquid and check for residue or do a silver nitrate test for salt precipitation.

Step-by-step solution

Initial Observation

First, observe the liquid physically. Water is colorless, odorless, and tasteless. Confirm these properties through observation, but remember that many liquids may also possess these characteristics.

Litmus Test for Water

Use litmus paper to check the acidity or alkalinity. Pure water is neutral and should not affect the litmus paper color (red stays red and blue stays blue).

Conduct Boiling Point Test

Boil a small sample of the liquid. Pure water boils at 100°C (212°F) at standard atmospheric pressure. Observe the temperature at which the liquid begins to boil to verify if it is close to this range.

Solution Testing for Salt

To check for dissolved salt, first evaporate a sample of the liquid by heating it. If salt was present, a white crystalline residue should remain after all the water has evaporated.

Conduct a Precipitation Test

Add a few drops of silver nitrate to another sample of the liquid. If there is salt, a white precipitate of silver chloride will form due to a chemical reaction with chloride ions.

Key concepts

Litmus Test

A litmus test is a simple and quick method to test for acidity or alkalinity in a solution. It's an easy experiment where you dip a piece of litmus paper into the liquid and observe any color change. The paper comes in two colors – red and blue. - In acidic solutions, blue litmus paper turns red. - In alkaline solutions, red litmus paper turns blue. - However, in neutral solutions like pure water, neither the red nor the blue litmus paper changes color.
This makes the litmus test handy for confirming if the liquid you have is water, as pure water should not alter the color of the litmus paper. Remember, this test alone can't distinguish water from other neutral substances, but it's an excellent first step in the investigation of liquid properties.

Boiling Point Determination

Boiling point determination is another useful method to identify if a liquid is water. This involves heating the liquid and observing the temperature at which it boils. For water, this is typically 100°C (212°F) at sea level. To conduct the test, you: 1. Heat a small sample of the liquid. 2. Use a thermometer to carefully monitor the temperature as it heats up. 3. Note the exact temperature when the liquid starts to boil.
If the boiling point is around 100°C, it's a strong indication that the liquid is water. However, factors like altitude and atmospheric pressure can slightly alter boiling points, so consider these when interpreting results.

Precipitation Reaction

A precipitation reaction is a process where two solutions are mixed, and an insoluble solid called a precipitate forms. This reaction is particularly useful in detecting specific ions, like chloride ions, in a solution. For example, to test for salt in water: - Add a few drops of silver nitrate to the sample. - If chloride ions (from dissolved salt) are present, a white precipitate of silver chloride will form.
This is a straightforward method to check for dissolved salts, confirming their presence if the white precipitate appears, providing a visual cue for chemical reactions occurring in your solution.

Dissolved Salts Analysis

Analyzing dissolved salts in a liquid involves several steps to confirm their presence. After confirming the liquid's neutrality with a litmus test and its boiling point, you proceed to confirm if salts exist dissolved in the water. - Heat a small amount of the liquid to evaporate the water. - Observe any residue left behind. A white crystalline residue indicates dissolved salt.
It's essential to perform additional tests, like the precipitation reaction, to verify these findings. These methods give deeper insights into the chemical makeup of the solution, ensuring comprehensive analysis to confirm salt presence.