1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Acid or Base and Chemistry of Taste

  1. Jul 11, 2007 #1
    Can somebody tell me the color the following items turn when purple Cabbage Indicator is added:

    Hydrogen peroxide
    Isopropyl alcohol
    Saline solution
    Tonic water

    and can you tell me if the items listed above are Acid or Base or Neutral

    Please and Thank uo:)
  2. jcsd
  3. Jul 12, 2007 #2


    User Avatar
    Homework Helper
    Education Advisor
    Gold Member

    Can you find a reference book or article which gives the pH range and colors for that "purple Cabbage" indicator material? Do you have any information about the composition of those listed materials so as to judge their effect on pH? You should be able to answer your own questions.

    A quick guess is that the purple indicator may be much like phenolphalein in its pH behavior --- only a "quick guess", not necessarily the correct guess.
  4. Jul 12, 2007 #3
    Okay I get it you want me to find the Ph scale which is the one below. Then you want me to google each item to find there ph and that should tell me the color that each one turn and if it is acidic, netural, or a base.
    pH 2 4 6 8 10 12
    Color Red Purple Violet Blue Blue-Green Greenish Yellow

    Thank u
  5. Jul 12, 2007 #4
    I kinda made a big mistake were using red cabbage indicators not purple, but when you make the substance its purple.
    Here's how to make it:

    Making Red Cabbage Indicator

    Put 1/2 cup of finely chopped red cabbage leaves in a jar and add 1/2 cup of hot water. Stir and crush the leaves with a spoon so that the red pigment in the leaves colors the water.

    Continue this crushing until the water has turned a distinct, rich purple color.

    Strain the liquid through a coffee filter to separate it from the cabbage leaves and throw the leaves away.

    ***The remaining liquid is a pH indicator: a substance that can be used to determine the pH of a substance. ***
  6. Jul 12, 2007 #5
    Use the key below to determine whether the substance is an acid, base or is neutral. Record your results in the Data Table.

    If the indicator turns the test solution red or pink, the solution is an acid.

    If the indicator and solution together are a purple color, this indicates that it is neutral—neither an acid nor a base.

    If the indicator turns the solution blue or green, the solution is a base.
  7. Jul 12, 2007 #6
    Can somebody tell me if im right :tongue2:, so far I have:

    Item color acid/ base/ neutral

    Water - purple - netural
    Isopropyl alcohol-red-acid
    Aspirin- dark pink- acid
    Tonic water-pink-acid

    Im missing:
    Saline solution
    Hydrogen peroxide

    Can somebody tell me what they are and the color. I think there all bases beteween the color of blue and green but im not sure. :confused:

    Help please:blushing:
  8. Jul 12, 2007 #7


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    I would rethink the answer for isopropyl alcohol. The rest look good.

    Regarding the 'missing' ones you show... remember that pepto-bismol is a product designed to treate heartburn (acid indigestion). Of course its pink which makes it hard to observe a color change of an indicator. Saline solution has several meanings, the simplest of which is saltwater solution. It also means a saltwater solution that is formulated to accomplish something (lactated Ringers, acetated Ringers, Phosphate Buffered Saline, etc...). Some of these other types of saline have been pH adjusted to physiological pH. Hydrogen peroxide is reactive with the indicator and may bleach it. If it is dilute enough, this may not happen very quickly and you can observe a color briefly. Most commercially available hydrogen peroxide has substances in it that stabilize the reactive peroxide against decomposition. Those stabilizers can be either acidic or basic...
  9. Jul 12, 2007 #8
    Thank you chemisttre.
    Okay so far I have Saline solution as base and the color greenish blue is that correct.

    I'm still missing
    Isopropyl alcohol
    Hydrogen peroxide
  10. Jul 12, 2007 #9


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    I wouldn't think so. Does dissolving salt (NaCl) into water affect pH? What is physiological pH?
  11. Jul 12, 2007 #10
    I know That Salt is a base by looking through other websites that used salt to perform this experiment.
  12. Jul 12, 2007 #11


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Those websites were wrong about salt....
  13. Jul 14, 2007 #12
    salt is the substance formed when an acid reacts with a base, eg. HCl+NaOH=NaCl+H2O so it is neither an acid or a base, but some residual NaOH can make it basic, NaOH is a strong base so even a little would turn it basic
    what is your margin of error?
    how pure is the salt?
    Think of what pepto-bismol would normally be used for
  14. Sep 20, 2007 #13
    Caught in the act!!!!

    Your a student from Florida virtual school and you have posted an assignment. I have been notified and may have to take the necessary action!

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook