A student conducted an experiment where she added HCl (a very strong acid) to 4 test tubes containing unknown solutions. She tested the pH of each of the solutions before and after the addition of the acid using pH paper. The color of the pH paper before and after adding acid to the unknown solutions can be seen in the table below. For reference: [tex]$pH 2=$[/tex] red; [tex]$pH 4=$[/tex] orange; [tex]$pH 7=$[/tex] yellow; [tex]$pH 9=$[/tex] green; [tex]$pH 14=$[/tex] purple.
| Test Tube | Before adding acid | After adding acid |
| --------- | ------------------ | ----------------- |
| A | Yellow | Red |
| B | Purple | Yellow |
| C | Yellow | Yellow |
| D | Green | Red |
Which of the tubes is the most likely to contain artificial cytoplasm?
Multiple Choice
Tube D
Tube A
Tube C
Tube B
Answer (1)
Analyze the pH changes in each test tube after adding HCl.
Tube A: pH change = 5.
Tube B: pH change = 7.
Tube C: pH change = 0.
Tube D: pH change = 7.
The smallest pH change is in Tube C, indicating it's most likely to contain artificial cytoplasm. T u b e C
Explanation
Understanding the Problem We are given the initial and final pH values of four test tubes after adding a strong acid (HCl). We need to determine which test tube is most likely to contain artificial cytoplasm, which acts as a buffer to resist pH changes.
Buffer Solutions A buffer solution resists changes in pH. Therefore, the test tube with the smallest change in pH after adding HCl is most likely to contain artificial cytoplasm.
Analyzing pH Changes Let's analyze the pH changes in each test tube:
Tube A: pH changed from yellow (pH 7) to red (pH 2). The pH change is 7 - 2 = 5.
Tube B: pH changed from purple (pH 14) to yellow (pH 7). The pH change is 14 - 7 = 7.
Tube C: pH remained yellow (pH 7). The pH change is 7 - 7 = 0.
Tube D: pH changed from green (pH 9) to red (pH 2). The pH change is 9 - 2 = 7.
Identifying the Most Likely Tube Comparing the pH changes, Tube C shows the smallest change (0). This indicates that Tube C is the most resistant to pH changes upon the addition of acid, suggesting it is most likely to contain artificial cytoplasm.
Final Answer Therefore, the most likely tube to contain artificial cytoplasm is Tube C.
Examples
Buffers are essential in biological systems, like our blood, to maintain a stable pH. For example, the pH of human blood needs to stay around 7.4. If the pH goes too high or too low, it can be life-threatening. Buffers in the blood, such as bicarbonate, help neutralize acids or bases that enter the bloodstream, preventing drastic pH changes. This is similar to how artificial cytoplasm maintains a stable pH in a lab setting, ensuring that experiments are not affected by pH fluctuations.
