Chem Lab #6 Help

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Lesson 6 Lab: Titrations and Natural Acid/Base Indicators


Begin by viewing the following Thinkwell videos

27.1.6  CIA Demonstration: Titrations
16.2.2  CIA Demonstration: Natural Acid-Base Indicators?
(NOTE: The second video is sort of a supplement to the first, and shows how this applies to your daily life. Feel free to try some of the things listed in the video, but be sure to report back to the class regarding the results of your experiments!)

After you watch the above video, answer the questions below in sufficient detail:

(a) (1 pts.) In YOUR OWN WORDS, what is a titration? What type of reaction is it?

Answer:

(b) (1 pts.) What is the BALANCED chemical reaction for the titration performed in this lab demonstration? What does this balanced equation tell us that is so important with respect to this particular lab exercise, and how do you use this information in this lab?

Answer:

(c) (1 pts.) What is the name of the special piece of glassware used in this titration exercise? Why use it as opposed to, say, a graduated pipette--what is special about the glassware used here? How is it SPECIFICALLY used in this lab?

Answer:

(d) (2 pts.) In a titration, assuming it is carried out just like the one in this lab exercise, how do you determine the number of moles of base used? Explain in detail, showing all work.

Answer:

(e) (2 pts.) In a titration, assuming it is carried out just like the one in this lab exercise, how do you determine the number of moles of acid used? How do you then use this information to determine the concentration of the acid? Explain in detail, showing all work.

Answer:

(f) (1 pts.) In this titration example, how do you know when the reaction is complete? What is used (be specific), and how does it work? What is the official name (Dr. Yee mentions this) of the end of this reaction?

Answer:

(g) (2 pts.) How does the hydrogen ion (H+) [or the hydronium ion (H3O+)] and the hydroxide ion (OH-) fit into all of this? What is their role in this reaction? In the case of this particular example that you watched, where would each of these ions have come from?

Answer:

(h) (2 pts.) Suppose I wanted to calculate the pH of the acid used in this titration. How (explain) can I use the results from this experiment to do this? What would the pH be in this case? Show all work.

Answer:

(i) (2 pts.) Throughout the video there were various suggestions that came up that were useful tips for you to remember that would help make sure your titration was a successful one. Dr. Yee mentions a few, but there were also some that came up within the images on the screen. What were at least 2 tips for carrying out a successful titration?

Answer:

(j) (1 pts.) In the second video listed above, red cabbage was demonstrated as a natural indicator, and the hydrangea flower was also mentioned. Do some research (include references) and find and discuss another natural acid/base indicator that was not mentioned in the video.

Answer:

(k) Suppose your instructor handed you a bottle of sulfuric acid of unknown concentration. The chemistry department was considering using it for a summer program for elementary students to test rock samples to see if they contain limestone. However, they don’t want to give it to the kids if it is too strong, and noone in the department was willing to drop some on their skin, and all the graduate students and TA’s were already guinea pigs in other experiments, and the department did not want to compromise the data from that research in any way. So, the task falls to you, the eager undergraduate student.
(2 pts.) First, explain, using a chemical equation, and then describing it, how sulfuric acid could test for the presence of limestone. What specific reaction would be taking place, and what easily noticeable phenomenon would you be looking for when doing this test? Why?

   Answer:

[ii] (3 pts.) Suppose you take a 25.00 mL sample of this sulfuric acid solution. You then titrate it with a 0.1322 M potassium hydroxide solution. A volume of 41.22 mL of potassium hydroxide was required to complete the titration. What is the concentration of this unknown sulfuric acid solution?

   Answer:

?


?DON'T FORGET TO INCLUDE REFERENCES IN ORDER TO FULLY DEVELOP YOUR ANSWERS AND GO BEYOND THE BASICS OF THE QUESTION!!!

1. (a) A titration is a method to determine the concentration of something. You do this by taking a measured amount of the stuff you want to analyze. Then you slowly add another chemical that will react with it. You keep adding until no more will react. You measure the amount that you added of the second chemical. This is usually done by adding it from a burette -- a long tube with milliliter markings and a valve at the bottom. You also have to know the concentration of the second chemical. Once you know the amount of stuff you start with and the concentration and amount of the added chemical, then you can figure out the concentration of the stuff.

For example, if you have 25 ml of acid and want to know the concentration. Use a base like sodium hydroxide (NaOH) to react with (neutralize) it. You will need an indicator to tell when it's all neutralized. A typical one to use is phenolphthalein. A couple of drops will look clear in the acid, but when it's neutral or actually slightly basic, it will turn pink. So now, fill your burette up with the known concentration of the NaOH, say 1M (1 molar). Read the starting point of the burette, and run some of the NaOH into a flask that you can swirl around to keep it mixed. After adding a bit of the NaOH, it will start to turn pink, but then as you swirl it, the color will disappear. Now add a drop at a time until the color stays. If you do this perfectly, it will be a really faint pink. Now read the burette again and subtract to determine the volume that you added. You can now figure out the concentration of the acid by the equation:

(volume of acid) times (concentration of acid) = (volume of NaOH) times (concentration of NaOH)

If the volume of acid was 25 ml and the volume of added NaOH was 37 ml and the concentration of NaOH was 1.0 M, then:

(25 ml) (concentration of acid) = (37 ml) (1.0 M)

concentration of acid = (37) (1.0) ÷ 25 = 1.48 M

I know that this is probably more than what you wanted, but I hope you understand it now.

Thanks.

Hi medgirl90,

For question (b) what is the BALANCED chemical reaction took place

?CH3COOH(aq) + NaOH(aq) = Na(CH3COO)(aq) + H20(l)

Really need help with this too. Struggling!

The reaction equation above is the neutralization of acetic acid with sodium hydroxide.

A basic solution contains positive ions and OH- ions:

NaOH Na+ + OH-

An acid solution contains H3O+ ions and negative ions

CH3COOH + H2O H3O+ + CH3COO-

When a basic solution is mixed with an acid solution, the positive ions and the negative ions bond.
Na+ + CH3COO- CH3COO-Na+(aq)

And the H3O+ and OH- bond.
H3O+ + OH- 2H2O

The complete equation is shown below:

NaOH(aq) + CH3COOH(aq) + H2O CH3COO-Na+(aq) + 2 H2O(l)

• Subtract 1 H2O from both sides

NaOH(aq) + CH3COOH(aq) CH3COO-Na+(aq) + H2O(l)
The equation is balanced, and I hope this makes sense to you!!

A generic double replacement reaction equation is shown below.
A+B- + C+D- A+D- + C+B-
Na+ OH- + H+ CH3COO- Na+ CH3COO- + H2O

The neutralization of an acid and a base is a double replacement reaction.

Any help out there on the rest of the questions?

A burette, used because it is more precise.

This is what I have so far. Any help on the 2nd half?


(a) (1 pts.) In YOUR OWN WORDS, what is a titration? What type of reaction is it?

Answer: A titration is the process used to determine the concentration of something. It is a neutralization reaction.

(b) (1 pts.) What is the BALANCED chemical reaction for the titration performed in this lab demonstration? What does this balanced equation tell us that is so important with respect to this particular lab exercise, and how do you use this information in this lab?

Answer: The balanced chemical reaction for the titration performed in this lab demonstration is: NaCOOH(aq)+NaOH(aq)=Na(CH3COO)(aq)+H2O(l). A basic solution has positive ions and OH- ions like Na+ and OH-. Acid solutions have H3O+ and negative ions like CH3COOH + H20 -> H3O+ + CH3COO-. When basic and acid mix, positive and negative ions will bond: Na+ + CH3COO- -> CH3COO-Na+(aq) and the H3O+ and OH- will also bond.

(c) (1 pts.) What is the name of the special piece of glassware used in this titration exercise? Why use it as opposed to, say, a graduated pipette--what is special about the glassware used here? How is it SPECIFICALLY used in this lab?

Answer: A burette is used, its long, thin tube allows for one to get a precise measurement of liquid in the lab, it is used to measure the amount of sodium hydroxide.

(d) (2 pts.) In a titration, assuming it is carried out just like the one in this lab exercise, how do you determine the number of moles of base used? Explain in detail, showing all work.

Answer: NaCOOH(aq)+NaOH(aq)=Na(CH3COO)(aq)+H2O(l)
moles=m*v
moles NaOH = 35.42mL NaOH*1L/1000mL*0.502 mol/L
=0.01778 mol NaOH

(e) (2 pts.) In a titration, assuming it is carried out just like the one in this lab exercise, how do you determine the number of moles of acid used? How do you then use this information to determine the concentration of the acid? Explain in detail, showing all work.

Answer: Since acetic acid and NaOH react in a 1:1 ratio, the moles of NaOH are equal to the number of moles of the acetic acid. You would divide the number of moles by the volume of the vinegar (20mL) which gives you the concentration of acetic acid in the vinegar (0.89 M CH3COOH).
m=0.01778 mol * 1/20mL * 1000mL/1L
=0.89 mol/L
=0.89 M CH3COOH

(f) (1 pts.) In this titration example, how do you know when the reaction is complete? What is used (be specific), and how does it work? What is the official name (Dr. Yee mentions this) of the end of this reaction?

Answer: You know that the reaction is complete when the liquid turns pink. You use a base like NaOH to neutralize the acid. Phenolphthalein is the indicator. You continue to add drops of phenolphthalein to the liquid until it turns pink and then you swirl the liquid around. If the color goes away, you continue to add the drops until the liquid stays a light pink color.

Need answers to the last 2 questions. Help, please!!

(g) (2 pts.) How does the hydrogen ion (H+) [or the hydronium ion (H3O+)] and the hydroxide ion (OH-) fit into all of this? What is their role in this reaction? In the case of this particular example that you watched, where would each of these ions have come from?

Answer:

(h) (2 pts.) Suppose I wanted to calculate the pH of the acid used in this titration. How (explain) can I use the results from this experiment to do this? What would the pH be in this case? Show all work.

Answer:

(i) (2 pts.) Throughout the video there were various suggestions that came up that were useful tips for you to remember that would help make sure your titration was a successful one. Dr. Yee mentions a few, but there were also some that came up within the images on the screen. What were at least 2 tips for carrying out a successful titration?

Answer:

(j) (1 pts.) In the second video listed above, red cabbage was demonstrated as a natural indicator, and the hydrangea flower was also mentioned. Do some research (include references) and find and discuss another natural acid/base indicator that was not mentioned in the video.

Answer:

(k) Suppose your instructor handed you a bottle of sulfuric acid of unknown concentration. The chemistry department was considering using it for a summer program for elementary students to test rock samples to see if they contain limestone. However, they don’t want to give it to the kids if it is too strong, and noone in the department was willing to drop some on their skin, and all the graduate students and TA’s were already guinea pigs in other experiments, and the department did not want to compromise the data from that research in any way. So, the task falls to you, the eager undergraduate student.
(2 pts.) First, explain, using a chemical equation, and then describing it, how sulfuric acid could test for the presence of limestone. What specific reaction would be taking place, and what easily noticeable phenomenon would you be looking for when doing this test? Why?

   Answer:

[ii] (3 pts.) Suppose you take a 25.00 mL sample of this sulfuric acid solution. You then titrate it with a 0.1322 M potassium hydroxide solution. A volume of 41.22 mL of potassium hydroxide was required to complete the titration. What is the concentration of this unknown sulfuric acid solution?

Any help for the last couple of questions?