Multiple Choice
Which of the following is commonly measured using a chemical test in the identification of ions and gases?
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4. BONUS: Lab Techniques and Procedures
Test for Ions and Gases
Multiple Choice
When iodine comes into contact with starch, which of the following observations is made?
A
The solution turns colorless.
B
A white gas is released.
C
A red precipitate forms.
D
A deep blue-black color appears.
Verified step by step guidance1
Understand the chemical interaction between iodine and starch: iodine molecules fit inside the helical structure of amylose, a component of starch.
Recognize that this interaction causes a charge-transfer complex, which changes the way light is absorbed and reflected, resulting in a color change.
Recall that the characteristic observation when iodine contacts starch is the appearance of a deep blue-black color, indicating the formation of this complex.
Note that the other options (colorless solution, white gas release, red precipitate) do not correspond to the known iodine-starch reaction.
Conclude that the deep blue-black color is a qualitative test commonly used to detect the presence of starch in a sample.
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