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chem assignment 10

Hi everyone,

Your hands-on experiment is coming up soon. It is Module 10 and will open up next month.
Here is the list of materials you will need (this list is also in the syllabus):

1) thermometer (30-200°F)

2) effervescent antacid tablets

3) timer (you can use your cell phone)

4) 3 clear drinking cups/glasses

5) ½ cup (4 oz) measuring device

You will also need to have access to hot and cold water.

chem assignment 10

Name __________________________

Module 10

Post-Lab Assignment

Short Answer (30 points)

Answer the following questions based on material covered in this module. (5 points each.)

(You must use complete sentences when answering each question.

1-point deduction per question not answered in complete sentences.)

1) Based on your results, which antacid is most efficient, 1 tablet of Tums or ¼ teaspoon of baking soda? Explain.

2) In this experiment, is the NaOH neutralizing the antacid? How do you know?

3) If you were to overshoot the endpoint and the final solution is a deep violet-blue, what would that do to the perceived efficiency of the antacid being analyzed? (Would it appear to be more or less efficient than it actually is?) Explain.

4) Think through the entire procedure and describe one possible unavoidable experimental error that could contribute to a poor analysis for the antacids. (Misreading the glassware and calculation errors do not count as unavoidable experimental errors.)

5) What would happen if you forgot to add the bromophenol blue indicator to the upset stomach? Explain.

6) What does your graph from the Hands-On Experiment tell us about the reaction you carried out? Explain.

chem assignment 10

REACTION RATES – Hands-On Experiment

1

Data Collection and Results Pages Name ___________________
Date ____________________

Observations:

Hot water: ______________________________________________________________

Room temp water: ________________________________________________________

Cold water: ______________________________________________________________

Convert °F to °C:

Find your averages:

Water Sample Average Temp (°C) Average Time (seconds)
Hot water
Room temp water
Cold water

Water Sample
Trial #1
Temp
(°F)

Trial #1
Time

(seconds)

Trial #2
Temp
(°F)

Trial #2
Time

(seconds)

Trial #3
Temp
(°F)

Trial #3
Time

(seconds)
Hot water
Room temp water
Cold water

Water Sample
Trial #1
Temp
(°C)

Trial #2
Temp
(°C)

Trial #3
Temp
(°C)

Hot water
Room temp water
Cold water

2 EXPERIMENT 4: DENSITY

2

Graph area

chem assignment 10

REACTION RATES – Hands-On Experiment

Purpose: To investigate the effects of temperature changes on the progression of a
chemical reaction.

Introduction
Chemical reactions occur to different extents depending on the conditions of the reaction and
on the thermodynamics of the chemical reaction itself. Thermodynamics is the science of the
relationship between heat and other forms of energy. In this experiment, we will be
investigating how temperature change affects the rate of a chemical reaction.

If you have ever used effervescent antacid tablets, like Alka-Seltzer, you know that when you
drop them into a glass of water, as instructed, they fizz. The fizz, or effervescence, is due to
the formation of gas bubbles. If you recall from the Properties and Changes lab, the evolution
of a gas, or effervescence, when you mix substances together is evidence of a chemical
reaction occurring. The chemical reaction that is occurring when you drop an effervescent
antacid tablet into water is as follows:

3NaHCO3(s) + C6H8O7(s) –® Na3C6H5O7(aq) + 3CO2(g) + 3H2O(l)

(sodium bicarbonate + citric acid –® sodium acetate + carbon dioxide + water)

When the sodium bicarbonate and citric acid are in the solid tablet form, they cannot react
with one another because the particles are unable to move and collide with one another.
Collision of particles is required for chemical reactions to take place. The water breaks the
solid bonds of the tablet, allowing the particles to collide and react with one another. The
bubbles we see (and/or hear) are the formation of carbon dioxide gas, which is the evidence
that lets us know a chemical reaction is occurring.

According to collision theory, as temperature increases, more particles in a reaction will
acquire the minimum amount of kinetic energy that is required for the reaction to occur, which
then leads to a larger number of effective collisions and a higher rate for the reaction.

If the temperature of a reaction is changed, the rate will change accordingly. It is generally
accepted that the rate of a reaction approximately doubles when the temperature is increased
by about 10℃ (50°F).

*Formula to change °F to °C: °F – 32 = (1.8) x °C

Equipment/Materials
Thermometer (30-200°F range), effervescent antacid tablets, timer, 3 clear cups/glasses, ½
cup (4 oz) measuring device, access to hot and cold water

Experiment 13: REACTION RATES

Procedure
(Using a pen or pencil, record by hand all of your data and results on the Data Collection
and Results Pages.)

Ø You will need to have access to water of different temperatures: hot water, room
temperature water, and ice cold water. You will run three trials of the experiment at
each temperature, for a total of 9 trials.

Ø To get hot water, use the hot setting from a water faucet. To get room temperature
water, leave lukewarm tap water out on the counter for about an hour so that it can
stabilize to the temperature of the room. Make sure you leave out enough for a few
trials so that you do not have to wait another hour. To get cold water, leave cold tap
water in your refrigerator for about an hour OR put cold tap water into a bowl of ice
and let sit for a few minutes.

Ø If you do not have access to tap water, you can use bottled water and follow the above
process for room temperature and cold. For hot, you can use a microwave to heat the
water.

Ø Do not mix and match the water sources. Use the same water type for each trial; either
use only tap or only bottled water.

1. Add ½ cup (4 ounces) of hot water to a clear glass or cup. Record the temperature in
°F.

2. Drop an effervescent antacid tablet into the water and begin the timer. Record what

you see. How vigorously is it bubbling?

3. Stop the timer when the tablet has disappeared. Record the time it took to do so.

4. Repeat two more times with fresh samples of hot water. If you are re-using the same
glass or cup, be sure to rinse it out between trials.

5. Convert °F into °C for each trial.

6. Repeat steps 1 – 5 for the other two water temperatures. Be sure that your times are
recorded in seconds. (1 minute = 60 seconds)

7. Calculate the averages of the temperature readings and times.

8. Using the graph area provided, create a line graph of the average temperature (y-axis)
vs. the average time (x-axis) in order to see the change in the rate of reaction based on
the change in temperature. (Just connect the dots. We do not need a best fit straight
line for this experiment.) Be sure to give your graph a title and label your axes.

chem assignment 10

Experiment 10

EFFICIENCY OF ANTACIDS

Data Collection and Results Pages Name: __________________________
Date: ___________________

Part I:

Concentration of HCl = ________ Volume of HCl (stomach acid) = __________

Part II:

Identity of active ingredients of the antacids:

Tums: ______________________________________________

Baking Soda: _________________________________________

Mass of Tums sample = ________________

Mass of baking soda sample = ________________

Part III:

Concentration of NaOH = _________

Tums Baking soda

Initial Buret Reading of NaOH

Final Buret Reading of NaOH

Volume of NaOH used

(subtraction – volume cannot be negative!)

Volume of stomach acid neutralized by NaOH

(equal to volume of NaOH used)

Tums = _____________

Baking soda = ____________

Experiment 10: EFFICIENCY OF ANTACIDS

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Volume of stomach acid neutralized by antacid

(volume of stomach acid not neutralized by NaOH)

Tums = _____________

Baking soda = ____________

Volume of acid neutralized for every gram of antacid used:

(units should be in mL/g, so take your volume and divide by mass)

Show your calculations.

Tums: Baking soda:

Tums = _____________

Baking soda = ____________

chem assignment 10

Experiment 10:
EFFICIENCY OF ANTACIDS

1

Purpose: The efficiencies of two different antacids to neutralize stomach acid are to be
analyzed and compared.

Introduction:

Stomach acid (or gastric acid) is mainly an aqueous hydrochloric acid solution
(approximately 0.1 M HCl). HCl is secreted by the stomach to help in the digestion of foods
by breaking down large molecules into smaller ones to be absorbed by the small intestines.
The human body can produce and secrete 2 to 3 liters of stomach acid per day.

When we overindulge in food an excess of stomach acid is produced and secreted, resulting
in the uncomfortable feeling of indigestion. If the excess acid were to make its way back up
to the lower esophagus, we would experience heartburn.

Heartburn, due to excess stomach acid, can be alleviated by neutralizing the acid with an
antacid. For example, the active ingredient in Alka-Seltzer is sodium bicarbonate
(NaHCO3). The reaction of sodium bicarbonate with stomach acid produces carbonic acid,
which immediately decomposes to water and carbon dioxide:

NaHCO3 (s) + HCl (aq) ¾® H2CO3 (aq) + NaCl (aq)
H2CO3 (aq) ¾® H2O (l) + CO2 (g)

The overall reaction is

NaHCO3 (s) + HCl (aq) ¾® H2O (l) + CO2 (g) + NaCl (aq).

The “fizz” produced when Alka-Seltzer is placed in acid is due to the carbon dioxide
escaping out of the solution.

Baking soda is pure sodium bicarbonate and works just like Alka-Seltzer as described
above. It is much cheaper. However, one has to be careful with the dosage, which is
roughly ½ teaspoon per 8-oz glass of water. Since it is not dispensed as a tablet, one could
accidentally “overdose” on bicarbonate.

Other antacids may have carbonates or hydroxides, such as calcium carbonate or aluminum
hydroxide. Carbonates are similar to bicarbonates in that they produce water and carbon
dioxide. Hydroxides react in a typical acid-base neutralization to form water and salt. An
example of each is shown below:

CaCO3 (s) + 2 HCl (aq) ¾® H2O (l) + CO2 (g) + CaCl2 (aq)
Al(OH)3 (s) + 3 HCl (aq) ¾® 3 H2O (l) + AlCl3 (aq)

In this experiment you will begin by preparing a simulated stomach acid solution. A higher
concentration than what is normally found in the stomach (1.00 M instead of 0.1 M HCl) is
used here so that we do not have to use unmanageably large volumes of solutions in the

2 EXPERIMENT 10: EFFICIENCY OF ANTACIDS

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laboratory. Antacid is added to the acid, and the amount of acid not neutralized by the
antacid is to be determined by measuring exactly how much NaOH is needed to finish the
neutralization. An efficient antacid should produce a solution that requires little of the
NaOH to complete the neutralization.

The method used for the analysis is called titration, which is a laboratory technique of
determining the concentration of an unknown solution by measuring the exact volume of a
solution of known concentration needed to completely react with the solute in the unknown
solution. In this experiment, the leftover stomach acid is being titrated with 1.00 M NaOH.
The volume of the NaOH solution is determined with the use of a buret. An indicator,
bromophenol blue, is used, which turns from yellow (when in an acidic medium) to blue
(when in a basic medium). Thus, when just enough (a stoichiometric amount) of NaOH has
been added to neutralize the leftover stomach acid, the solution will quickly change to blue.
This is called an endpoint, the point when an indicator changes color. In this reaction, the
endpoint is also the equivalent point, the point when both reactants in a reaction have
completely reacted, leaving no excess behind.

HCl (aq) + NaOH (aq) ¾® H2O (l) + NaCl (aq)

In this experiment, note that the balanced equation shows that one mole of HCl would
require one mole of NaOH. Therefore, at and only at the exact point when the solution turns
from yellow to blue, the number of moles of NaOH would equal to the number of moles of
HCl. Since we are using the same concentrations (1.00 M) for both the HCl and NaOH, the
volume of NaOH that is required to neutralize the leftover HCl after the antacid has done its
job, is equal to the volume of HCl not neutralized by the antacid.

CONCEPT OF MOLARITY
Molarity is the number of moles of solute per liter of solution. Thus a solution labeled as
6.00 M HCl means 6.00 moles of HCl are in one liter of the solution.

Molarity =

Laboratory Techniques Used in This Experiment

Pipeting Technique

Pipets are accurately calibrated to deliver designated volumes of liquids. The proper
technique of pipeting a sample involves filling the pipet above the calibration mark
with the use of a pipet bulb or pipet pump. NEVER use your mouth to draw up the
liquid. Hold your index finger over the top of the pipet to keep the liquid above the
mark, wipe the outside of the pipet with a piece of Kimwipe, and then let the liquid
slowly drain until the meniscus reaches the calibration line. Any drop hanging outside
the tip of the pipet is removed by touching the tip of the pipet to the rim of the liquid
container. The pipet is then shifted to the container into which you are to deliver the

Liters #
moles #

calibration
mark

EXPERIMENT 10: EFFICIENCY OF ANTACIDS 3

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sample and is then permitted to drain without immersing it in the sample. The drop
hanging OUTSIDE on the tip of the pipet after it has drained is removed by touching
the tip to the inside wall of the container just above the liquid level. DO NOT BLOW
OR SHAKE OUT THAT LAST DROP INSIDE THE TIP. The pipet has been
calibrated with that last drop remaining in the tip. If you blow or shake that drop into
the container, you would have transferred one drop too much. With the use of the wash
bottle, direct a small stream of deionized water to the inside surface of the container to
wash adhering drops of the sample to the bottom of the container.

How to Record Buret Readings

1. The curved surface of a liquid is called a meniscus. Water has a meniscus that curves

down. It is important that you read the buret with the meniscus at eye level to avoid the
problems of parallax. You know you are not at eye level if the marking on the buret on
the backside is visible, as in Fig.11.1. If you are at eye level, the markings should be as
shown in Fig. 11.2.

Fig. 11.1 Fig. 11.2

2. The scale on the buret goes from zero at the top to 50.00 mL at the bottom. It is easy to

forget and read it backwards. Read the burets to 2 decimal places. Remember you
should be reading the number indicated by the bottom of the meniscus.

Buret A Buret B Buret C Buret D

Buret Reading for Buret A = ______ Buret Reading for Buret C = ______
Buret Reading for Buret B = ______ Buret Reading for Buret D = ______

4 EXPERIMENT 10: EFFICIENCY OF ANTACIDS

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PROCEDURE
(Using a pen or pencil, record by hand all of your data and results on the Data Collection
and Results Pages.)

You will be using two antacids: baking soda and Tums. It might be necessary to repeat one
or more of the trials if you were to miss the endpoint. The usual recommended dosage for
Tums is to chew 2 to 4 tablets. With baking soda, it is suggested to be ½ teaspoon every 2
hours. In this experiment, we will be comparing the efficiency of 1 tablet of Tums and ¼
teaspoon of baking soda.

Part I: Preparing the Upset Stomach

1. Obtain two 250-mL Erlenmeyer flasks from your drawer and label them as Tums and
baking soda.

2. Label your 400-mL beaker as “waste” and set it aside. Obtain a clean and dry 250-
mL beaker and label it as “HCl.” Obtain a clean and dry 100-mL beaker and label it
as “NaOH.”

3. Pour 20 mL of 1.00 M HCl into the HCl beaker. Obtain a 25-mL volumetric pipet.
Draw about a third of the HCl solution into the pipet and roll it around while holding
the pipet horizontally as demonstrated by your instructor. This is to rinse the inside
walls of the pipet. Let the solution drain into the “waste” beaker. Do not let it drain
back into the HCl beaker.

4. Repeat the rinse two more times, each time letting the rinse solution drain into the
“waste” beaker.

5. Discard any acid remaining in the 250-mL beaker into the “waste” beaker as well.
6. Obtain approximately 80 mL of fresh 1.00 M HCl in the same “HCl” beaker.
7. Following the directions given by your instructor, pipet exactly 25.0 mL of 1.00 M

HCl to each of the two flasks. Remember not to blow or shake out that last drop in
the tip of the pipet. Record this volume to 3 significant figures.

8. Add 2 or 3 drops of bromophenol blue indicator to each flask.
9. With the wash bottle, wash down the inside walls of the flasks with deionized water

so that there are no acid drops hanging on the upper walls of the flasks.

Part II: Adding the Antacid

10. Record the identity and amount of the active ingredient(s) of Tums and baking soda.
11. Obtain a mortar and pestle. If it looks dirty, just wipe it clean with paper towels.

DO NOT WASH OR GET IT WET IN ANYWAY.
12. Crush and grind one tablet of Tums with the mortar and pestle.
13. Using the balance, tare a weighing boat to zero. With your spoonula, transfer all of

the resulting fine powder to the weighing boat, and then record the mass using all
decimal places shown on the balance. Then, carefully transfer the antacid from the
weighing boat to the Erlenmeyer flask labeled “Tums”. (Do not spill any during the
transfer.)

EXPERIMENT 10: EFFICIENCY OF ANTACIDS 5

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14. Next, tare a clean (new) weighing boat to zero. Remove it from the balance pan, and
add one small scoop of baking soda to it. Return the weighing boat to the balance
pan. Continue removing the boat and adding a small amount of baking soda until the
balance reads between 1.2 and 1.5 g. Record the mass to all the decimal places
shown on the balance. (This is about ¼ teaspoon of baking soda.) Carefully transfer
the antacid from the weighing boat to the Erlenmeyer flask labeled “baking soda”.

15. You have now partially neutralized your two “upset stomachs” with antacid samples.
16. In Part III, you will determine how much of the acid did not get neutralized.

Part III: Completing the Neutralization

17. PREPARING THE BURET:
a. Obtain a 50.00-mL buret and set it up on a ring stand with a buret clamp as

shown in the Figure 10.3 below. Position a magnetic stir-plate so that the buret is
directly over the center of the stir-plate.

b. Into the NaOH beaker, pour about 10 mL of the 1.00 M NaOH.
c. Make sure the stopcock is in the CLOSED position and transfer about half of the

contents of the beaker into the buret.
d. Hold the buret in a near-horizontal position with the opening over the “waste”

beaker.
e. Rotate the buret so that the inside surface of the buret is coated with the NaOH

solution while it is being drained SLOWLY into the “waste” beaker.
f. Repeat Steps (c) through (e) with the other half of the NaOH solution in the

NaOH beaker.

stopcock

magnetic
stir-plate

Figure 10.3

buret clamp

6 EXPERIMENT 10: EFFICIENCY OF ANTACIDS

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g. Pour 50 mL of 1.00 M NaOH into the “NaOH” beaker. This should be enough
for both trials.

h. Hold the buret at a slight angle. Make sure the stopcock of the buret is closed,
then pour all of the NaOH solution into the buret.

i. Place your “waste” beaker under the buret, turn the stopcock to the fully open
position and allow about 5 mL of NaOH solution to drain out of it. This should
get rid of all of the air pocket in the buret tip. It is essential that there are
absolutely no air bubbles remaining in the tip. It is usually difficult for
beginning chemistry students to recognize the presence of air bubbles in the tip.
Ask for assistance if you are not sure.

18. Hold the buret at eye level, and with the help of the volume-reading card you had
prepared in an earlier experiment, read and record the buret reading to two decimal
places (0.01 mL) under “Initial Buret Reading.” Place the buret back on the buret
clamp.

19. Obtain ONE magnetic stir-bar from your instructor. Rinse it with deionized water
and the carefully slide it into your Tums Erlenmeyer flask, and place the flask under
the tip of the buret. The flask should be close to the center of the magnetic stir-plate.
The tip of the buret should be inside the flask, slightly below the lip of the flask so
that no NaOH solution can splash out during the subsequent steps.

20. Place a piece of white paper under the flask to help you detect more readily the
change in color during the titration.

21. Turn on the magnetic stirrer and slowly increase the speed to medium speed. Be
sure you are using the STIR knob and not the HEAT knob. You do NOT want to
heat your solution! You also do not want to stir it at a speed such that droplets may
splash out of the flask.

22. Adjust the stopcock so that the NaOH solution comes out very slowly, drop by drop.
It should be slow enough that when necessary, you can turn off the stopcock
immediately before the next drop comes out.

The bromophenol blue indicator is yellow when the solution is acidic and it turns
blue when the solution is basic. You want to add just enough NaOH to neutralize
all of the acid. Initially, when the first pale blue begins to appear, it will quickly
disappear as you stir the contents of the flask. As you near the endpoint, you will
have to stir longer before the blue disappears, and you should slow down the
drops. You have reached the endpoint when the solution stays a pale blue even
after 30 seconds of stirring. The endpoint is very sharp. It takes only one drop
(or half a drop if you are careful enough) to bring it from yellow to pale blue. You
must stop the addition immediately. If you were to allow extra drops to fall into
the solution you would have passed the endpoint and your data would be incorrect.

Note: Be sure that at no point should the NaOH level go below the graduated
portion of the buret (below 50.00 mL). If you think you are going to run out of
NaOH in the buret, notify your instructor who will decide what you should do.

EXPERIMENT 10: EFFICIENCY OF ANTACIDS 7

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23. Continue adding the NaOH solution dropwise until a pale blue color persists after 30
seconds of stirring. Do not overshoot the endpoint.

24. After you have reached the endpoint, hold the buret at eye level, read and record the
buret reading (again to 0.01 mL) under “Final Buret Reading.”

25. From the difference in the two buret readings you can calculate the volume of
1.00 M NaOH you have used to neutralize the remaining “stomach acid” that the
antacid did not neutralize. CALCULATE THIS IMMEDIATELY!

26. The solution in the flask is essentially neutral and can be poured down the drain. Be
careful the stir-bar does not go down the drain also! Rinse the stir-bar under running
tap water and then rinse it with deionized water before you use it again for the next
trial.

27. Repeat Steps 19 through 26 for the baking soda trial. If your buret is not leaking, the
“Final Buret Reading” of the previous trial would become the “Initial Buret
Reading” of the next trial. You probably will not need to refill the buret at any point
unless you have made a mistake and have to repeat a trial.

28. FINAL CLEAN UP: The contents of the flasks can be discarded down the drain. The
white residue on the walls of the flasks MUST be removed. Rinse the flasks out with
a small amount of HCl solution provided IN THE HOOD. The rinse should go into
the designated waste container. The excess HCl or NaOH from the beaker or buret
should be discarded in the same waste container.

Return the stir-bar to your instructor. The mortar and pestles should be washed and
wiped dry with paper towels. All labels should be removed from your beakers and
flasks.

The buret (with the stopcock OPEN) and the pipet should be rinsed with hot tap
water and then GENTLY placed in the special buret container marked “DIRTY”
with the tips pointing up.

*Answers to example buret readings in introduction (remember that the last digit is
the uncertain digit – it is the only digit that can be slightly different from person to
person):

A) 43.65 mL B) 41.05 mL C) 0.25 mL D) 18.15 mL

Chem Assignment 10

Three Assignments for chem:

1. Part 1 – Assignment-  M10 Data Collection and Results Pages.pdf

2. Part2- Assignment-Hands-on Part 2 Data Collection and Results Pages.pdf

3. M10 Post_Lab Assignment .docx

Also attached corresponding reading material and 6 images. Attached note from teacher for this module

Due on 22nd April