Why does btb change color

Two Lab Reports

Acid-Base Chemistry

Hands-On Labs, Inc. Version 42-0137-00-03

Lab Report Assistant

This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate students’ writing of lab reports by providing this information in an editable file which can be sent to an instructor.

Exercise 1: Using pH Paper and the Indicator Bromothymol Blue (BTB)

Data Table 1. Data Collected from Exercise 1.

ID Number

Chemical Name

Chemical Formula

Hypothesis: Acid or Base

pH

BTB Color

Acid or Base?

11A

Acetic acid

CH3COOH

Acid

pH 2

Yellow

Acid

11B

Nitric acid

HNO3

Acid

pH 3

Yellow

Acid

11C

Sulfuric acid

H2SO4

Acid

pH 3

Yellow

Acid

11D

Phosphoric acid

H3PO4

Acid

pH 2

Yellow

Acid

11E

Sodium acetate

CH3COONa

Base

pH 7

Blue

Base

11F

Sodium bicarbonate

NaHCO3

Acid

pH 8

Blue

Base

11G

Sodium dihydrogen phosphate

NaH2PO4

Base

pH 0

Yellow

Acid

11H

Sodium hydrogen sulfate

NaHSO4

Acid

pH 6

Yellow

Acid

12A

Sodium hydrogen sulfite

NaHSO3

Acid

pH 5

Yellow

Acid

12B

Limewater

Ca(OH)2

Base

pH 9

Blue

Base

12C

Sodium phosphate

Na3PO4

Base

pH 13

Blue

Base

12D

Sodium hydrogen phosphate

Na2HPO4

Base

pH 7

Blue

Base

12E

Ammonium hydroxide

NH4OH

Base

pH 8

Blue

Base

12F

Hydrochloric acid

HCl

Acid

pH 2

Yellow

Acid

12G

Sodium carbonate

Na2CO3

Base

pH 10

Blue

Base

12H

Sodium hydroxide

NaOH

Base

pH 12

Blue

Base

Questions

A. When you created hypotheses to guess whether each chemical was an acid or base, what specifically did you look for in the chemical formulas?

I looked for OH- or H+ in the formula and if it was an H+ than the chemical is most likely acidic and OH- would be basic.

B. What is the value of using pH paper as an indicator?

You could find if it were a weak or strong acid or base by looking at the pH paper. With the pH paper, you would be able to determine the substances pH value number and not just if it’s acidic or basic.

C. What is the value of using BTB as an indicator? When might BTB be a better choice than pH paper?

To figure out the pH value we must add the BTB, green means it's natural, blue is base, and yellow is acidic. It’s useful to do this whenever you want to know if any chemical is acidic or basic.

D. Write the chemical equation of mixing nitric acid (HNO3) with water.

HNO3 (aq)+ H2O(aq) <—>H3O++NO3-

E. Write the chemical equation of mixing ammonia (NH3) with water.

NH3(aq) H2O —>NH4+(aq)+ OH-(aq)

F. What are the conjugate acids and conjugate bases of questions D and E?

The conjugate bases of D and E are NO3-and OH

Exercise 2: Acid-Base Reactions

Data Table 2. Acid-Base Reactions.

Row

1

2

3

4

5

6

A HCl

pH:

11

pH:

10

pH:

10

pH: 9

# drops NaOH:

5

B CH3COOH

pH:

0

pH:

9

pH:

0

pH: 12

# drops NaOH:

6

C C,H2SO4

pH:

6

pH:

9

pH:

11

pH:

14

pH:

13

pH: 12

# drops NaOH:

9

D H3PO4

pH:

2

pH:

5

pH:

6

pH:

6

pH:

12

pH: 7

# drops NaOH:

12

Questions

A. Visually analyze the wells in the plate. What information can be gleaned from each well based on the color of the BTB indicator after each reaction has occurred? How do you know if neutralization has occurred? Cite examples from the well plate reactions to support your answer.

Neutralization has happened when the resulting solution's pH will be less than 7. While looking at the reaction in the wells, you could see the BTB reacting with the chemical the color change can indicate the Neutralization has happed. But I think the most effective way was to use the pH test strip to determine the pH level to see if Neutralization has happed.

B. What factors determine if neutralization occurs during an acid-base reaction?

A neutralization reaction is when an acid and a base react to form water and a salt and involves the combination of H+ ions and OH- ions to generate water. The neutralization of a strong acid and strong base has a pH equal to 7.

C. Is the pH at the equivalence point always equal to 7? Explain your answer based on your experimental observations. Include a discussion of equivalence point pH values for strong versus weak acids.

There is no motivation behind why the pH ought to be seven at the equivalence point except if the acid being titrated is a strong acid, and the base from the Burette is a solid base. On the off chance that you are titration a frail acid with a solid base, the items will be a weak base and an exceptionally weak acid. So, pH will be >7.

D. In all the chemical reaction performed in Exercise 2, neutralization occurs when the pH is neutral (7) or basic (>7). Did any of the reaction not result in a color change of the BTB indicator from yellow (acid) to blue (base)? Explain why neutralization may not have occurred in one or more reactions.

I feel that some the chemicals that were neutralized combined well with the BTB resulting in their chemical reaction to be neutral as it is neither acidic nor alkaline and some did not blend because it may have been a weak acid it does not dissociate fully when it is dissolved.

Exercise 3: Testing the pH of Household Products

Data Table 3. Household Acids and Bases.

Household substance

Prediction:

(Acid, Base, or Neutral)

pH Value

Conclusion:

(Acid, Base, or Neutral)

Coffee w/Cream

Acid

pH 7

Neutral

Soda (Coke)

Acid

pH 3

Acid

Bleach

Base

pH 10

Base

Lysol

Acid

pH 7

Neutral

Isopropyl

Acid

pH 5

Acid

Questions

A. What properties did you use to determine whether the substances you tested were acid or base?

What I used were the pH strips to help me conclude whether the chemical/product I tested was acid or base.

B. Did any of your findings surprise you? Why or why not?

I was surprised by the coffee since the result came out to be neutral. I have always been told that it was acidic due to what it does to your teeth in long-term. But after thinking about it since there was cream in the coffee, it may have canceled the acidity in the coffee that would have made it an acid. Another one that I was surprised with was the Lysol since it is a cleaner, I thought it would be acidic to be able to clean thoroughly and remove all the grams.

My Findings

After working on this lab, I learned that not all things that you have been told might be correct for instance when I did the test on the coffee with cream it did not come out to be acidic. After thinking about it, I came up with a hypothesis that I wanted to test to see if I was correct and to my findings, I was right. So, I knew that the coffee I tested was not acidic with the cream. I took it upon myself to test another coffee without the cream, and the result was that black coffee is more acidic, I used a pH strip to check the coffee, and the result was a pH leave of 5 making it acidic. In conclusion, if you would like a coffee with less acidity add some cream to cancel it out.