Question

Hi I am working on my chemistry homework about acids and bases and I am confused on this question from a lab. We used grape juice and cranberry juice and we had to put HCl and NaOH in the test tube full of juice.

1. Referring back to procedure 1 of the experiment, which of the two juices is more useful as a general pH indicator and why? I think it is grape juice but I just don't know what to back my answer with. I appreciate the help!

Answer 1

Ans. A pH indicator is a substance that changes its color with change in pH.

Grape juice changes its color from reddish purple (acidic pH) to bluish purple (basic pH, around 8.0) when NaOH is added.

Cranberry juice changes its color from red (acidic pH) to dark red (acidic pH, around 4.8). So, the color change in acidic pH range itself. However, cranberry juice color also change its color to greenish purplish in basic pH.

Therefore, color change (the property of an indicator) is more consistent in grape juice- color change indicates basic pH range.

Cranberry juice first change color at pH around 5 (acidic pH itself), then in basic pH.

Type of Juice	Natural pH and color	First color change noted at
Grape juice	pH range : 2.0 – 4.2 Color- Reddish purple	pH : 8.0 Color : Bluish purple /black
Cranberry juice	pH range : 2.3 – 2.5 Color- Red	pH : 4.8 Color : Dark red

Both juices can equally be used as good pH indicator depending on your need if you know the color changes accurately.

However, when it comes to prefer a “general acid-base indicator” , a substance that changes color upon change in pH range (acidic, neutral, basic), the grape juice may be preferred because it changes color only when the pH changes from acidic to basic.