New User Special Price Expires in

Let's log you in.

Sign in with Facebook


Don't have a StudySoup account? Create one here!


Create a StudySoup account

Be part of our community, it's free to join!

Sign up with Facebook


Create your account
By creating an account you agree to StudySoup's terms and conditions and privacy policy

Already have a StudySoup account? Login here

Unknown Weak Acid Lab Report

by: Daisia Frank

Unknown Weak Acid Lab Report Chem 3510

Marketplace > Austin Peay State University > Chemistry > Chem 3510 > Unknown Weak Acid Lab Report
Daisia Frank
GPA 3.6

Preview These Notes for FREE

Get a free preview of these Notes, just enter your email below.

Unlock Preview
Unlock Preview

Preview these materials now for free

Why put in your email? Get access to more of this material and other relevant free materials for your school

View Preview

About this Document

Lab Report
Organic Chemistry
Dr. Matthews
Class Notes
organic, Chemistry, lab, report
25 ?




Popular in Organic Chemistry

Popular in Chemistry

This 9 page Class Notes was uploaded by Daisia Frank on Sunday September 25, 2016. The Class Notes belongs to Chem 3510 at Austin Peay State University taught by Dr. Matthews in Fall 2016. Since its upload, it has received 5 views. For similar materials see Organic Chemistry in Chemistry at Austin Peay State University.


Reviews for Unknown Weak Acid Lab Report


Report this Material


What is Karma?


Karma is the currency of StudySoup.

You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!

Date Created: 09/25/16
Daisia Frank CHEM 1121 Dr. Reed July 31, 2016 Determining the Identity of an Unknown Weak Acid Lab Report Introduction: In this experiment, a weak acid’s identity was determined using the method of titration for weak  acids.  The titration was performed with standard sodium hydroxide solution.  In order to do this, the titration had to be monitored by an indicator or pH meter.  A pH meter and LoggerPro  software on a computer were used to determine the equivalence point of the titration.   Buffer Region a Equivalen ce Volume Figure 1: Titration of 0.1M of acid by 0.1 M NaO(Just shown for illustration purposes)  (1) The equivalence point is the point where enough titrant (NaOH) has been added to the  analyte (unknown weak acid) that results in the analyte being neutralized.  Using this  equivalence point, the acid disassociation constant, Ka can then be determined for the unknown  acid titrated. Finally, the identity of the unknown acid can be concluded.  For the dissociation of  any weak acid, HA (2):  + – HA(aq) → H (aq) + A (aq) Eq.1   When a weak acid dissolves in water an equilibrium is established.  When the reaction is at  equilibrium the total concentrations of each reagent are constant and the acid dissociation  constant, K ca  be calculated:    + − [H ][A ] Eq. 2 K a    [HA]   The Ka should be a very small number because weak acids don’t disassociate completely and a  large Ka value indicates greater dissociation.  To solve for [H ]:  +   K [HA] ­   Eq. 3 [H ]= [A] Since Ka values are so small using pKa values are more beneficial to scientists as it allows them  to use whole numbers (pKa = ­logKa).  Titration curves happen due to the molar component of  the titrant and anylate.  When slowly adding the base to the weak acid solution the graph  exponentially increases.  Then, when the number of moles of base equals the number of moles of weak acid present, a sharp change (increase) in the curve of the graph can be observed: Figure 2: Plot of slope, ΔpH/ΔV, vs. mL NaOH based on Figure 1 titration (Numbers aren’t accurate) (2) After the sharp change in the curve, any base added just increases the pH and the graph  eventually levels off.  The graph can also be used to calculate the moles of acid present.  The  number of moles of acid to base is assumed to be 1:1, so the volume and concentration of added  base can be determined.  Finally, the identity of the unknown acid can be determined by  estimating the pKa and calculating the molar mas of the acid based on the quantity of solution  measured. Equipment/ Chemicals:  Unknown Weak Acid   50 ml 0.10 M KCl  100 ml volumetric flask  Buret  Ring stand/ clamp  pH Meter  NaOH solution  LabQuest Mini  Drop Counter  pH sensor  Stir plate Procedure: About 1.3­1.4 grams of unknown acid “H” were weighed and dissolved in 50 ml of 0.10  M KCl solution in a 100­mL volumetric flask.  Once all the solid was dissolved, the solution was diluted to the 100 mL mark with 0.10 M KCl.  LabQuest Mini was connected to the computer  and a drop counter was attached to a ring stand.  A pH sensor was inserted into the opening in  the drop counter.  Once connected, the computer displayed information from both the drop  counter and pH meter.  A stir plate and magnetic stir bar were obtained.  A buret was attached to  a utility clamp and ring stand.  The discharge opening was positioned 1 cm above the drop  counter.  A waste beaker was placed at the base of the stand and the buret was filled with about  25 ml of dH O2  The lower stopcock was opened completely while the top one was opened until  the flow of water was at a steady 1 drop a second.  All of the water was dispensed and the lower  stopcock was closed.  The buret was then filled with about 75 ml of NaOH.  To calibrate the  drop counter, 9­10 ml of the solution were dropped into a 10­ml graduated cylinder and the exact amount of NaOH dispensed was imputed into the computer.  In a 100 ml beaker 25 ml of dH O  2 were poured in and using a volumetric pipette 25.00 ml of the unknown weak acid solution was  poured in as well.  The beaker was placed on the stir plate with a magnetic stir bar inside.  The  pH probe was positioned inside the beaker and the stir plate was turned on.  The green arrow on  the computer was pushed to start the titration and the lower stopcock was opened fully.  The  titration proceeded until 10 ml after the equivalence point.  The data was saved and stored. Calculations: Calibration of Drop counter: 201 drops/ 8.9 ml = 22.58 drops/ ml Molar Mass unknown acid = grams weighed/ moles calculated 0.3498/ 0.00264 = 132.48 grams/ mol (Equivalence Volume) (Molarity Base) = mol OH ­ (0.01336 L)(0.1974 M) = 0.00264 moles of base pKa = 0.5(Equivalence Volume)  Midpoint of buffer region Graph 1: Trial 1 Titration Curve Graph 2: Titration Curve Moles of Acid Used (grams)  1.399 Total Volume of Prepared Acid Sample 100 mL KCl Concentration of Prepared Acid Sample (g/ ml) 0.02798 g/ ml Concentration of Base 0.1974 M NaOH Table 1: Concentrations and masses of acid and base samples (Unknown Acid: H) Trial 1 Trial 2 Volume of Acid Titrated (mL) 25 ml 25 ml Mass of acid titrated (g) 0.3498 0.3498 Equivalence Volume (V ) (mL) 13.36 10.94 e Moles of Base required for  0.00264 0.0022 equivalence Molar Mass of Unknown Acid 132.48 150.98 pKa of unknown acid 1.94 2.24 Table 2: Trials 1 and 2 data Average Molar Mass (g/mol) 141.73 Average pKa 2.09 Identity of Unknown Acid Potassium Bisulfate Table 3: Average Calculations and identity of unknown weak acid Identity percent error: 4.06% Discussion: The purpose of the experiment was to determine the identity of an unknown weak acid  through titration.  Titration is a process that involves a strong base as the titrant ­ for this  experiment NaOH solution ­ and a weak acid as the anylate ­ in this experiment the identity is  unknown.  Given Unknown acid “H” and NaOH solution, a titration curve/ graph was plotted  using LoggerPro.  Figure 1 shows the equivalence point, which is near the middle of the sharp  curve; the equivalence volume, which is the vertical line that corresponds to the volume for the  equivalence point; the buffer region, which is the portion of the curve before the sharp curve; and pH= pKa which is close to the middle of the buffer region.  The average equivalence volume was 12.15.  The volume and molar concentration of the base (titrant) that was added was used to  determine the moles of acid present: Molar Mass unknown acid = grams weighed/ moles calculated 0.3498/ 0.00264 = 132.48 grams/mol .  The average molar mass was 141.73.  Using the titration curve the pKa was found by finding  the midpoint of the buffer region.  The average pKa was 2.09 which is equivalent to the pH.   This seems accurate because the solution is in fact acidic.  Comparing the experimental molar  mass to actual values of actual compounds, the identity of the unknown acid was determined to  be Potassium Bisulfate.  Some sources of error included accidentally stopping the graph for trial  2 for about 30 seconds, which is the reason there is a jump after the equivalence point in Graph  2.  Additionally, miscalculations and misinterpretations of the graph could have led to inaccurate  values.  Overall, the experiment showed that titration is a beneficial process for determining the  identity of an unknown weak acid and titration curves can provide a lot of information regarding  its titrant and anylate, References: (1)Enduring Understanding 6.C: Titration Curves. (2005­2016). Retrieved August 01, 2016,  from (2) Department of Chemistry. (2010). UCCS (University of Colorado at Colorado Springs)  Chem 106 Laboratory Manual. Cengage Learning. Retrieved July 31, 2016.­Titration2.pdf (3) Department of Chemistry. (2016). Austin Peay State University Revision F16 Lab Manual.  Cengage Learning. Retrieved July 31, 2016.


Buy Material

Are you sure you want to buy this material for

25 Karma

Buy Material

BOOM! Enjoy Your Free Notes!

We've added these Notes to your profile, click here to view them now.


You're already Subscribed!

Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'

Why people love StudySoup

Steve Martinelli UC Los Angeles

"There's no way I would have passed my Organic Chemistry class this semester without the notes and study guides I got from StudySoup."

Allison Fischer University of Alabama

"I signed up to be an Elite Notetaker with 2 of my sorority sisters this semester. We just posted our notes weekly and were each making over $600 per month. I LOVE StudySoup!"

Jim McGreen Ohio University

"Knowing I can count on the Elite Notetaker in my class allows me to focus on what the professor is saying instead of just scribbling notes the whole time and falling behind."


"Their 'Elite Notetakers' are making over $1,200/month in sales by creating high quality content that helps their classmates in a time of need."

Become an Elite Notetaker and start selling your notes online!

Refund Policy


All subscriptions to StudySoup are paid in full at the time of subscribing. To change your credit card information or to cancel your subscription, go to "Edit Settings". All credit card information will be available there. If you should decide to cancel your subscription, it will continue to be valid until the next payment period, as all payments for the current period were made in advance. For special circumstances, please email


StudySoup has more than 1 million course-specific study resources to help students study smarter. If you’re having trouble finding what you’re looking for, our customer support team can help you find what you need! Feel free to contact them here:

Recurring Subscriptions: If you have canceled your recurring subscription on the day of renewal and have not downloaded any documents, you may request a refund by submitting an email to

Satisfaction Guarantee: If you’re not satisfied with your subscription, you can contact us for further help. Contact must be made within 3 business days of your subscription purchase and your refund request will be subject for review.

Please Note: Refunds can never be provided more than 30 days after the initial purchase date regardless of your activity on the site.