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Titration of Hydrochloric Acid with Sodium Hydroxide Lab, Lab Reports of Chemistry

John Carroll University (JCU)Chemistry

HCl solution is a strong acid and NaOH solution is a strong base

Typology: Lab Reports

2020/2021
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Austin Peay State University Department of Chemistry CHEM 1011
TitrationofHydrochloricAcidwithSodiumHydroxide
Revision SP12 RBR Page 1 of 7
Cautions:Hydrochloricacidsolutionisastrongacid.Sodiumhydroxidesolutionisastrong
base.Bothareharmfultoskinandeyes.Affectedareasshouldbewashedthoroughlywith
copiousamountsofwater.
Purpose: Thepurposeofthislabistodeterminetheconcentrationofahydrochloricacid
solutionusingacid‐basetitration.
Background:Titrationisatechniquethatchemistsusetodeterminetheunknown
concentrationofaknownsolution(weknowwhatchemicalisdissolved,butnothowmuchina
solution).Becauseweknowwhatthechemicalis,weknowhowitwillreactwithother
chemicalsandwecanusethatreactiontodeterminetheconcentrationofthesolutionby
measuringtheformationofproduct(s).Inthecaseofanunknownconcentrationofacid,we
canuseaknownconcentrationofhydroxidebase.Thistypeofreactionisaneutralization
reaction,wheresaltandwaterareproductsofthereaction:
Acid+BaseSalt+H2O
WecanuseapHindicator,achemicalthatchangescolordependingonthepH,toshow
uswhenthereactionhascompletelyneutralized.Thispoint,whereallacidwasconsumedand
thereisnoexcessofbase,iscalledtheequivalencepoint.Wecanusethisequivalencepointto
determinetheinitialconcentrationofacidusingaseriesofcalculations.Thegoalofthe
titrationistogetascloseaspossibletotheequivalencepointbycarefuladditionofthebase;
thiswillensurethecalculatedacidconcentrationisasclosetothetruevalueaspossible.You
willdothreetitrationsandaveragethetrials.
Thetermsbelowwillhelpyouunderstandtheterminologyusedthroughoutthe
experiment:
Titrant—thesolutionofknownconcentrationisalsocalledthestandardizedsolution.In
thislab,thetitrantissodiumhydroxidesolution.
Buret—along,cylindricalpieceofglassthatcanbeusedtodeterminesmall,accurate
quantitiesofasolution.Aburetiscontrolledbyastopcock,awhiteTeflonpiecethat
canbeturnedtodeliverthesolution.Themarkingsontheburetaresuchthatyoumust
subtracttheinitialreading(wherethetitrantlevelisinitially)fromthefinalreadingto
determinethevolumeofbasedelivered.Theburetmeasures2digitsafterthedecimal
pointaccurately.
Volumetricpipette/pipettebulb—athinglasstubewithonlyonemarkingusedto
measureaveryspecificvolumeofliquid.Youwilluseapipettebulbtodrawtheliquid
intothepipette.
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pf4
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Titration of Hydrochloric Acid with Sodium Hydroxide

Cautions: Hydrochloric acid solution is a strong acid. Sodium hydroxide solution is a strong base. Both are harmful to skin and eyes. Affected areas should be washed thoroughly with copious amounts of water.

Purpose: The purpose of this lab is to determine the concentration of a hydrochloric acid solution using acid‐base titration.

Background: Titration is a technique that chemists use to determine the unknown concentration of a known solution (we know what chemical is dissolved, but not how much in a solution). Because we know what the chemical is, we know how it will react with other chemicals and we can use that reaction to determine the concentration of the solution by measuring the formation of product(s). In the case of an unknown concentration of acid, we can use a known concentration of hydroxide base. This type of reaction is a neutralization reaction, where salt and water are products of the reaction:

Acid + Base  Salt + H 2 O

We can use a pH indicator, a chemical that changes color depending on the pH, to show us when the reaction has completely neutralized. This point, where all acid was consumed and there is no excess of base, is called the equivalence point. We can use this equivalence point to determine the initial concentration of acid using a series of calculations. The goal of the titration is to get as close as possible to the equivalence point by careful addition of the base; this will ensure the calculated acid concentration is as close to the true value as possible. You will do three titrations and average the trials.

The terms below will help you understand the terminology used throughout the experiment:

 Titrant—the solution of known concentration is also called the standardized solution. In this lab, the titrant is sodium hydroxide solution.  Buret—a long, cylindrical piece of glass that can be used to determine small, accurate quantities of a solution. A buret is controlled by a stopcock, a white Teflon piece that can be turned to deliver the solution. The markings on the buret are such that you must subtract the initial reading (where the titrant level is initially) from the final reading to determine the volume of base delivered. The buret measures 2 digits after the decimal point accurately.  Volumetric pipette/pipette bulb—a thin glass tube with only one marking used to measure a very specific volume of liquid. You will use a pipette bulb to draw the liquid into the pipette.

Titration of Hydrochloric Acid with Sodium Hydroxide

 Phenolphthalein—a pH indicator. In acidic and neutral solutions, the indicator is colorless, but in a basic solution, the color is a vibrant pink. The higher the pH is, the stronger the pink color is. The equivalence point will be when the color is a very faint pink color. Keep your flask with acid and indicator over a white piece of paper to ensure you can see the color change.

Materials:  50 ‐mL Buret with clamp  Phenolphthalein indicator  125 mL or 250 ‐mL Erlenmeyer flasks  Buret funnel  250 ‐mL beaker  25 ‐mL volumetric pipette  Pipette bulb

Also of importance in titrations are the calculations you need to determine the unknown concentration of the acid. These calculations are outlined below. You may want to refer to your notes from lecture for additional examples.  Determination of moles of base delivered: After each titration, you will need to determine the number of moles of sodium hydroxide used. First, you will need to know the molarity of the solution (the solution has been previously standardized , meaning it has a very accurate molarity that has been experimentally determined). Write this down when you start the titration. Next, you must^ determine^ the^ volume^ of^ the solution delivered to reach the equivalence point. Next, you will find the moles of base used in the titration: ܸ ݁ݏ ܾܽ ݁݉ݑ݈݋ ݁ݏ ܾܽ ݂݋ ݕݐ݅ݎ݈ܽ݋ܯ ൈ ሻܮሺ ݉൬

*Note that the volume of base is in L, not in mL  Determine number of moles of HCl in flask: If you write the balanced reaction for the neutralization of sodium hydroxide and hydrochloric acid, you will see that the reaction proceeds in a 1:1 fashion. That is, for every hydroxide (OH‐) ion added, it can neutralize exactly one hydronium (H +) ion. This is not always the case for neutralization reactions, and is thus not always the case for acid‐base titrations. The general formula is below, where the determined moles of base from the equation above are multiplied by the stoichiometric ratio found by looking at the balanced equation: ݉ ሻ݁ݏܾܽሺ ݈݋ 1 ൈ

Titration of Hydrochloric Acid with Sodium Hydroxide

  1. Refill the buret with more sodium hydroxide solution if necessary. Record the new volume under trial 2 on the data sheet. Pipette another sample of acid and add the phenolphthalein as before and titrate as before.
  2. Conduct additional titrations until three of them differ by no more than 1.0%.
  3. Complete the data sheet and post‐lab questions. Show your work for full credit!!!

Titration of Hydrochloric Acid with Sodium Hydroxide

DATA SHEET

*Attach all of your calculations for full credit

Name:____________________________ Lab Partner:________________________________

Concentration of sodium hydroxide: __________________M

Balanced Chemical Equation of the titration reaction:

Trial 1 Trial 2 Trial 3 Trial 4

Initial buret volume (mL)

Final buret volume (mL)

Volume of base (mL)

Volume of base (L)

Moles of base (mol)

Acid to Base Mole Ratio

Moles of acid (mol)

Volume of acid (L)

Acid concentration (M)

Average concentration (M)

Percent Difference

Titration of Hydrochloric Acid with Sodium Hydroxide

PRE‐LAB

*Show all of your work for full credit

Name:_____________________________________

  1. How will you know when your titration is finished?
  1. Label the pH scale below with acid, base, and neutral, indicating numbers for each.
  2. On the scale above, use an arrow to show where your equivalence point is located.
  3. Write the neutralization reaction that occurs between hydrobromic acid (HBr) and lithium hydroxide (LiOH).
  4. What is the concentration of 10.00 mL of HBr if it takes 16.73 mL of a 0.253 M LiOH solution to neutralize it?