CHEMISTRY

Acid-Base Chemistry

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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.

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