Chemical Reactions

Litmus paper is a common indicator used to determine the acidity or basicity of a solution. Blue litmus paper turns red under acidic conditions, while red litmus paper remains red in acidic solutions. Acetic acid, with the chemical formula , is a well-known weak acid.

When red litmus paper is introduced into a solution of , it remains red because the solution is acidic. Red litmus paper only changes color in alkaline solutions, where it turns blue.

Thus, the correct behavioral observation is:

• Remains red

The reaction presented is between hydrochloric acid ( ) and zinc ( ):

When a metal reacts with an acid, it typically results in the formation of a salt and the liberation of hydrogen gas.

In this specific case, zinc reacts with hydrochloric acid to form zinc chloride ( ) and hydrogen gas ( ). The balanced chemical equation is:

This represents a single displacement reaction where zinc, a more reactive metal, displaces hydrogen ions in hydrochloric acid, forming zinc chloride and releasing hydrogen gas.

The correct answer is:

Methyl orange is a pH indicator commonly used in titrations because it has a clear and distinct colour change. It works efficiently within the pH range of 3.1 to 4.4.

In an acidic solution, the presence of excess hydrogen ions (H₃O⁺) triggers the colour change of methyl orange to red. This is due to the increased protonation of the indicator, which affects the light absorption spectrum, resulting in the display of a red colour.

To summarize, methyl orange exhibits a red colour in acidic conditions, specifically when the pH is below 3.1.