Question

what is a good hypothesis for this lab?? I need to write one.

Acid Base lab INSTRUCTIONS Acid-base indicators are used to let you know whether the solution you are working with is acidic or basic. We have many acid-base indicators available to us today, but the first indicators were made from natural compounds. The indicator that you will be making comes from purple cabbage and is simply called cabbage extract indicator. Procedure: Goggle red cabbage as an acid-base indicator. Go to websites to learn how to make red cabbage pH indicator Make your own pH paper strips using red cabbage indicator with filter paper (or coffee filter). Use the research to design a lab to complete at home. Remember: The procedure should be clear and complete steps that another experimenter could repeat. Test solutions of vinegar, baking soda (dissolve a small amount, 1 tsp, of baking soda into 15mL of water first) and plain water with the pH strips. Test at least 4 other household foods/beverages as non-toxic chemicals to test for pH values. Provide the chemical formula for all 7 of these items. Keep a small amount of the liquid indicator for this step: Slowly add the cabbage extract indicator solution into a small amount of vinegar (approximately 15ml) in a cup just until the colour changes. Repeat this with a solution of baking soda (1 teaspoon in 15 ml of water) until you see a colour change. Mix them together and record what happens. What happens if you mix the vinegar and baking soda solutions together after they have the indicator in them? What solution is this reaction similar to and why? Data: Include (with APA reference) a table of approximate colours of red cabbage indicator solutions at different pH levels and a standard pH table showing colours and numbers to compare your results to. Pictures of your substances and results. A table showing your substances and their pH, based on the colours. State whether each is acid, base or neutral. Discussion questions: What is the significance of “neutral” on the pH scale? What is the colour and pH number of a neutral solution? What happens if you mix the vinegar and baking soda solutions together after they have the indicator in them? What solution is this reaction similar to and why? In the Discussion with reference to your assigned pH values of the seven substances, explain strong and weak acids and bases, and give examples from your lab as references for each. What could you do to neutralize a spill of concentrated acid before cleaning it up to ensure you didn’t get burned? Reference information from the text as well as your observations from the lab (Hint: the mixing of the vinegar and baking soda solutions and noting the colour change)

Answer 1

An indicator is typically a chemical that changes color if it comes in contact with an acid or a base. Red cabbage contains a water soluble pigment molecule called flavin (an anthocyanin). Very acidic solutions will turn anthocyanin a red color. Neutral solutions result in a purplish color. Basic solutions appear in greenish-yellow. Therefore, it is possible to determine the pH of a solution based on the color it turns the anthocyanin pigments in red cabbage juice. The color of the juice changes in response to changes in its hydrogen ion concentration. pH is the -log[H+]. Acids will donate hydrogen ions in an aqueous solution and have a low pH (pH 7). How basic or acidic a solution depends on the amount of hydrogen ions in it. A basic solution accepts hydrogen ions (or donates electron pairs as hydroxide ions) whereas an acidic solution donates hydrogen ions (or accepts electron pairs). An indicator, like anthocyanin, responds to the levels of hydrogen ions in the solution. Anthocyanin and other biological pigments absorb certain wavelengths of light and reflect others, and it is the reflected light we see that makes them appear a certain color. Depending on the levels of hydrogen ions in the solution, the indicator pigment undergoes a chemical reaction that changes its chemical structure, making it reflect a different wavelength of light and thereby change color.

Red Cabbage pH Indicator Colors

pH	2	4	6	8	10	12
Color	Red	Purple	Violet	Blue	Blue-Green	Greenish Yellow

Procedure to prepare red cabbage indicator

Step 1 peel off three or four big cabbage leaves and put them in a blender filled one-half full with water. Blend the mixture on high until you have purple cabbage juice. Alternatively, Place the cabbage in a large beaker or other glass container and add boiling water to cover the cabbage. Allow at least ten minutes for the color to leach out of the cabbage.

Step 2 Pour the purplish cabbage liquid through a strainer to filter out all of the big chunks of cabbage. Filter out the plant material to obtain a red-purple-bluish colored liquid. This liquid is at about pH 7. The exact color you get depends on the pH of the water.

Step 3 Pour about 50 - 100 mL of your red cabbage indicator into each 250 mL beaker.

Step 4 Add various household solutions to your indicator until a color change is obtained.

Step 5 You can make your own pH paper strips using red cabbage indicator. Take filter paper (or coffee filter) and soak it in a concentrated red cabbage juice solution. After a few hours, remove the paper and allow it to dry (hang it by a clothespin or string). Cut the filter into strips and use them to test the pH of various solutions. Cut the dried paper into thin strips. Dip the strips into various liquids to test their pH. The redder the strip turns, the more acidic the liquid is. The greener the strip turns, the more basic the liquid is. If it stays purple, you guessed it, the substance you’re testing is probably neutral.

Experiment:

Step 1 Take three glasses which is three-fourths full with cabbage juice.

Step 2 Add a little vinegar to the first glass of cabbage juice. Stir with a spoon and notice the color change to red, which indicates that vinegar is classified as an acid.

Step 3 In the second glass, add a solution of baking soda (1 tsp of baking soda in 15ml of water) . The solution turns green, indicating that this chemical is a base.

Step 4 Add vinegar or lemon juice until a reddish color is obtained. Then add baking soda.  The solution turns neutral and the colour of the solution remains same.

Data

pH of Red Cabbage indicator and colour	Standard pH range and colour	Substance	Color after reaction with Red Cabbage indicator	Acid or base
pH 2-Red	pH 2 - Red	Vinegar CH3COOH	Red
pH 4-purple	pH 4-orange	Baking soda NaHCO3	Green
pH 6-violet	pH 6-yellow	Lemon juice C6H8O7
pH 8-Blue	pH 8 - Blue	Glucose solution C6H12O6
pH 10-Blue-green	pH 10- violet	Tamarind (Potassium bitartrate, KHC4H4O6)
pH 12- Greenish yellow	pH 12- Blue-Green	Turmeric

Please perform the experiment and submit the observations

Discussion questions:

What is the significance of “neutral” on the pH scale?

On a pH scale neutral solutions will have a pH of 7 or otherwise solutions having a pH of 7 is called neutral solutions

What is the colour and pH number of a neutral solution?

pH as discussed above will be 7. It will not react with the indicator. In this case it will remain purble blue for red cabbage indicator.

What happens if you mix the vinegar and baking soda solutions together after they have the indicator in them?

Mixing vinegar and baking soda makes it a neutral solution and the solution will remain the same withgout any colour change.

What solution is this reaction similar to and why?

It will be a neutral solution.

In the Discussion with reference to your assigned pH values of the seven substances, explain strong and weak acids and bases, and give examples from your lab as references for each.

Solutions of strong acids in the lab like HCl, H₂SO_4, HNO3 are acidic hence will show red or red-purple colour with the indicator. Solutions of strong bases like NaOH and KOH will have basic pH and show green colour when reacted with the indicator. From the experiment observation please see the colour change and categorise them as strong acids and bases after completing the experiment.

What could you do to neutralize a spill of concentrated acid before cleaning it up to ensure you didn’t get burned? Reference information from the text as well as your observations from the lab (Hint: the mixing of the vinegar and baking soda solutions and noting the colour change)

From the experiment performed recall the neutralisation experiment. When there is an acid spill try to neutralise it with a base before cleaning to neutralise it. In this case instead of using strong bases like NaOH and KOH try to use NaHCO₃ or Na₂CO₃ to avoid vigorous reaction and avoid burns and be safe before cleaning.