Multiple Choice
A student performs a Benedict's test on a sample to detect the presence of reducing sugars. After heating, the solution changes from blue to brick-red. What does this result indicate?
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4. BONUS: Lab Techniques and Procedures
Test for Ions and Gases
Multiple Choice
Which test is commonly used to identify the presence of carbon dioxide gas?
A
Place moist red litmus paper in the gas; it turns blue.
B
Add hydrochloric acid to the sample; effervescence occurs.
C
Bubble the gas through limewater; a milky white precipitate forms.
D
Expose the gas to a glowing splint; the splint relights.
Verified step by step guidance1
Understand that the problem asks for a common test to identify carbon dioxide (CO\_2) gas.
Recall that carbon dioxide is an acidic oxide and reacts with calcium hydroxide (limewater) to form calcium carbonate, which is insoluble and appears as a milky white precipitate.
Write the chemical reaction for the test: \(\mathrm{CO\_2 (g) + Ca(OH)\_2 (aq) \rightarrow CaCO\_3 (s) + H\_2O (l)}\).
Recognize that bubbling the gas through limewater and observing the formation of a milky white precipitate is a classic and reliable test for CO\_2.
Note that other options (moist red litmus turning blue, effervescence with HCl, glowing splint relighting) correspond to different gases or reactions and are not characteristic tests for CO\_2.
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