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    LAB REPORT PREPARATION OF STANDARD SOLUTION

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    47K views9 pages

    Lab Report Preparation of Standard Solution

    Uploaded by

    CRSFZ

    Copyright:

    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd
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    of 9

    Title:

    Preparation of Standard Solutions.

    Objectives:
     To know the preparation techniques of standard base solutions.
     To understand the concept of dilution and its calculation.

    Date of experiment:
    24 September 2019.

    Introduction:
    In titration, acid in buret will reacts to base in the conical flask in a known
    concentration to form water and a salt and involves the combination of H+
    ions and OH- ions to generate water .This reaction is known as neutralization
    reaction.This is we called as standard solution.

    The standard solution can prepared by weighed method.The mass of


    solute is calculated and weighed.After that the solute will be dissolved with
    distilled water in a beaker and it will transfered into volumetric flask. More
    distilled water added to get the required volume and concentration of the
    solution. Standard solution also can be prepared by dilution method.

    The process of dilution is involving mixing of a concentration solution with


    additional solvent to give a larger final volume.Thus, we can know the
    relationship of the molarity before and after the dilution process.This means
    that the molarity before the dilution is directly proportional to the molarity after
    the dilution.

    M1V1=M2V2
    Where,
    M1=Initial molar concentration
    M2=Final molar concentration
    V1=Initial volume of solution

    1
    V2=Final volume of solution
    Apparatus:
    Analytical balance, beaker 100 mL, burette 50 mL, conical flask 250 mL,
    dropper, funnel, glass rod, pipette 25 mL, volumetric flask 100 mL, distilled
    water.

    Chemicals:
    Hydrochloric acid,HCL 0.1M, Sodium hydroxide,NaOH, thymol blue indicator.

    Experimental procedures:

    a) Preparation of standard solutions

    1. 2.00-2.50 gram of solid sodium hydroxide was accurately weighed in a dry


    100 mL beaker and the weight of the sodium hydroxide was recorded.
    2. 30 mL of distilled water was added into the beaker and the solution was stir
    until dissolve.
    3. The solution was removed into a 100 mL volumetric flask by using cone-
    shaped funnel and a glass rod.The beaker and glass rod was rinsed
    with the distilled water.
    4. The distilled water was carefully added into volumetric flask until it
    reached the calibration mark.Then, a stopper was placed and the flask
    was slowly shaked.

    b) Dilution

    1.25 mL of the sodium hydroxide solution from procedure a) was pipetted


    and placed it into a 100 mL volumetric flask.
    2.Distilled water was added until it reached the calibration mark.Then, a
    stopper was placed and the flask slowly shaked.

    2
    c) Standardizing the solutions

    1. 25 mL of the sodium hydroxide solution obtained from procedure b) was


    pipetted and placed into a 250 mL conical flask.
    2. 3 or 4 drops f thymol blue indicator was added into the conical flask.
    3. 0.1M of standardized hydrochloride acid was filled into burette until it
    reached the zero mark.
    4. The sodium hyroxide from step number 2 was titrated with the
    standardized hydrochloric acid from step 3 until first change in colour
    was seen.It was changed from colour of blue to yellow.
    5. The volume of standardized hydrochloric acid used to change the colour
    was determined.
    6. With extra care, the procedure c) from step 1 until 5 was repeated twice.

    Results:

    a) Preparation of standard solutions

    1. Weight
    Weight of beaker + solid NaOH : 58.2268 g
    Weight of beaker : 55.7779 g
    Weight of solid NaOH : 2.4489 g

    2. Calculate the concentration of the prepared sodium hydroxide solution


    in
    g/L.

    Weight of NaOH= 2.4489 g


    Volume of distilled water used=0.10 L

    Therefore,
    The concentration of NaOH solution= 2.4489 g / 0.10 L
    = 24.489 g/L.

    3. Calculate the concentration of the prepared sodium hydroxide in molar.

    Concentration in g/L= Molar mass x Molarity.

    Therefore,
    Molarity=concentration in g/L / Molar mass.

    3
    =24.489 g/L / 39.997 g/mol
    =0.6123 mol/L.

    b) Dilution

    1.Calculate the number of dilution (dilution factor) made.

    Dilution factor=Final volume of solution/ Initial volume of solution

    Initial volume of NaOH=25 mL


    Final volume of NaOH=100 mL

    Therefore,
    DF=100 mL/ 25 mL
    =4

    2.Calculate the concentration of diluted sodium hydroxide in molar.

    M1V1=M2V2

    M1=0.6123 mol/L M2=?


    V1=25 mL V2=100 mL

    Therefore,
    (0.6123 mol/L)x(25 mL)=(M2)x(100 mL)
    M2=(0.6123 mol/L x 25 mL)/ (100 mL)
    =0.1531 mol/L

    c) Standardizing the solutions.

    1. Result of titration:
    Molarity of standardized hydrochloric acid: 0.1 M
    Volume of pipette used : 25 mL

    Reading of burette (mL) No. of titration


    1 2 3
    Final reading 41.50 39.80 39.90
    Initial reading 0.00 0.00 0.00
    Volume of HCl 41.50 39.80 39.90
    Average volume of HCl 40.40

    4
    2. Calculate the molarity of the titrated sodium hydroxide.

    HCl + NaOH NaCl + H20

    MaVa = a
    MbVb b

    Therefore,

    (0.1 M)(40.40 mL)= 1


    (Mb)(25.00 mL) 1

    Mb=(0.1 M)(40.40 mL)


    (25.00 mL)

    =0.1616 M

    3.Calculate the molarity of the original sodium hydroxide used.

    M1V1=M2V2

    Therefore,
    (M1)(25 mL)=(0.1616M)(100 mL)

    M1=(0.1616M)(100 mL)
    25 mL

    M1=0.6464 M

    5
    Discussion:

     In this lab session we can calculated the concentration of prepared NaOH


    is 0.6123 mol/L while the titrated NaOH is 0.1616 M and the concentration
    of original NaOH used is 0.6464 M.The percentage different of
    concentration prepared NaOH and original NaOH is 5.57%.The differ of
    concentration is due to slight errors in the process of measuring the
    weight of the solid NaOH as the presence of air currents that can affect
    the intricate mechanisms of the analytical balance and some errors during
    titration process.

     We can know and identify that HCl solution is a standardized solution


    because it has the accurate and known concentration a substance which
    Is 0.1 M.The HCl was used to help determine the concentration of NaOH
    Solution which the concentration is unknown.

     We can know the process of titration is involving the neutralization


    reaction.1 moles of HCl will reacts with 1 moles of NaOH to produce 1
    moles of NaCl and 1 moles of molecule water.Then, the accurately
    measured amount of standardized solution which is HCl solution added
    during titration to the NaOH solution in the conical flask until the colour of
    the thymol blue indicator changes from pale blue to pale yellow that is
    indicating the endpoint of the titration.

     We recommended to follow the correct procedure based on the manual


    lab and use the conical flask instead of beaker during titration to avoid
    chemocal spillage during the experiment.We also must apply the right
    techniques of titration to get the accurate result at the end.

     Using the right techniques of titration is very crucial. A right handed person
    must titrate use left hand and swirl the conical flask using the right hand.

    6
     We should follow up the precaution of the titration experiment before the
    experiment started to avoid any error and get the accurate value.For
    examples we must make sure no air bubbles in the nozzle of the burette
    and make sure that our eyes are parallel to the meniscus of burette and
    pippete reading.

    Conclusion:

     The concentration of prepared NaOH is 0.6123 mol/L while the titrated


    NaOH is 0.1616 M and the concentration of original NaOH used is
    0.6464 M.
     The concept of dilution is M1V1=M2V2, so the molarity of solution before
    dilution is directly proportional to the molarity of solution after dilution.

    Questions:

    1. Give the meaning of standardized solution.


    Standardized solution is a solution that contain a known and accurate
    concentration of a substance.

    2. State various uses of a conical flask.


    1.It is used for the preparation of microbial cultures in microbiological.
    2.The tapered sides and narrow neck of the flask allow the contents of the
    flask to be mixed by swirling, without the risk of spillage.
    3.It can be used to measure the volume of liquids. But this is not
    recommended for very accurate measurements of volume.
    4.It is placed under the burette during titration process.
    5.Its narrow necks can support filter funnels.
    6.The mouth of the flask can be closed using a cork to stop gaseous
    substances from escaping.

    3. During the titration process, can a beaker be used instead of conical


    flask? Why?

    7
    Can not use a beaker instead of conical flask because beaker has a wide and
    large open surface and it will increase the probability to chemicals spillage
    occur during experiment.Besides that it will be harder to swirl the beaker
    during titration as the whole body has the same size not like a conical flask
    which has a narrow neck to ease people to hold and swirl it.

    4. Compare the molarity of NaOH solution obtained from result a) 3 and c)


    3.
    The molarity of NaOH solution obtained from a) 3 is 0.6123 mol/L while in a) 3
    the molarity is 0.6464 M. The molarity of NaOH from a) 3 is smaller than the
    molarity of NaOH from c) 3.

    5. In an acid-base titration reaction, a 25 mL of NaOH solution requires


    23.30 mL 0f 0.093 M HCl solution.Therefore, calculate the molarity of
    the NaOH solution.
    HCl + NaOH NaCl + H20

    MaVa = a
    MbVb b

    Mb=Molarity of the NaOH solution.

    Therefore,

    (0.093 M)(23.30 mL)=1


    (Mb)(25.00 mL) 1

    Mb=(0.093 M)(23.30 mL)


    (25.00 mL)

    =0.0867 M

    References:

     https://study.com/academy/lesson/standard-solution-definition-
    method.html
     https://www.slideshare.net/RodneyPujada/report-1-prepare-and-
    standardize-a-01-m-naoh-solutions

    8
     Zeynep Eslek and Aysen Tulpar . Solution Preparation and Conductivity
    Measurements: An Experiment for Introductory Chemistry. Journal of
    Chemical Education 2013, 90 (12) , 1665-1667. DOI: 10.1021/ed300593t

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