Wednesday, October 26, 2011

IB Biology, IA, EE on glucose quantification assay using colorimeter for glucose diffusion experiment

IB Biology IA, EE, glucose assay/quantification with colorimeter using DNS
IA and EE on Glucose Quantification
1. 1% glucose std prepared (1g in 100ml)
2. 2 fold serial dil ( 1%, 0.5%, 0.25%, 0.125%, 0.0625%)
3. Add 2 ml of 1% glucose + 0.25ml of DNS (3,5 dinitrosalicylic acid) into a 50ml test tube.
4. Repeat step 1 to 3 with diff glucose concentration
5. Place all tubes in boiling water bath for 5 mins for colour formation. ( red brown)


6. Transfer 0.5 ml of sol from tube to cuvette and added 1.5ml of water to dilute it
7. Set visible spectrophotometer at 487nm.
8. Prepare a blank - 2ml water + 0.25ml DNS in test tube. Transfer 0.5ml to cuvette and add 1.5ml water to dilute it.



9. Measure absorbance at 487nm
10. Plot std calibration curve
11. Beer's Law works only for dilute solution.
12. Range for glucose ( 0.5%, 0.25%, 0.125%, 0.0625%,  0.03125%)
14. Watch video for clarification





Video, Glucose Quantification with DNS/Visible Spec

Experiment using glucose quantification
How surface area to vol ratio affect the diffusion of glucose from sweet potato strip measured with visible spec using DNS as a colour  formation?
Glucose quantification steps

  • 2 fold serial dil on 1% glucose std
  • Add 2ml glucose std + 0.25ml DNS in test tube
  • Leave in boiling water bath for 5 mins
  • Transfer 0.5ml to cuvette and add 1.5ml to dilute it
  • Measure Abs at 487nm
  • Blank done following above steps but using 2ml of water instead of glucose. 





Experiment on diffusion of glucose from sweet potato. ( Surface to volume ratio)
Sweet potato cut into 16 strips compared to 1 long uncut strip

  • Leave strips in 10 ml water over 24hrs 
  • Pipette 2ml sol and add 0.25ml DNS
  • Leave in boiling water bath for 5mins
  • Transfer 0.5ml into cuvette and add 1.5ml water to dilute it
  • Measure Abs at 487nm
  • Blank done following above steps, using 2 ml water 


Calculation of glucose from standard calibration curve
Standard Calibration Curve

  • Glucose diffusion rate = Abs change over 24hrs
  • Abs for 16 strips taken and conc is = 0.1467%
  • Abs for 1 strip taken and conc is = 0.0695%
  • Rate glucose diff = 0.1467/24 =0.00611%/hr
  • Rate glucose diff =0.0695/24 = 0.00289%/hr

Tips to make it work
* Glucose/DNS sol must be diluted with water as Beer's Law only applies for dilute sol
* Glucose sol range must be around 1% to 0.1% for colour determination.
* All item can be purchased from Carolina Biologicals or Kemtecscience
Easy Research Question for SL/HL on glucose expt
  • Starch hydrolysis with diff enzymes in producing glucose
  • Effect of pH, temp, heavy metal inhibitors, ionic salts on enzymatic hydrolysis of starch into glucose quantified using the above technique
Click HERE for different IA/EE using glucose/DNS techniques
Click HERE on glucose quantification and preparation of DNS solution.
Click HERE to purchase DNS kit
Click HERE to view MSDS toxicity of DNS.

Friday, October 21, 2011

IB Biology diffusion of beetroot pigment measured using visible spectrophotometer

IB Biology on effect of ethanol/SDS on diffusion of beetroot pigment.
Effects of ethanol and SDS on the diffusion of beetroot pigment measured using visible spec
Steps to follow
  • Cut beetroot into blocks, place in water to remove red pigment due to cutting
  • Prepare 2 fold dilution of SDS/Ethanol and place 2 ml into well
  • Find max wavelength for red pigment by pipetting 1.5ml into cuvette







Max Wavelength determined using visible spectrophotometer
  • Pipette 1.5ml red pigment (diluted) into cuvette to determine the max wavelength
  • Beer Lambert Law works only for diluted beetroot solution
  • 583nm was taken

Procedure/Steps
  • Cut blocks are placed in water to wash away pigment due to cutting
  • Place blocks in diff SDS/Ethanol conc for 5 mins
  • After 5 mins, pipette solution into cuvette
  • Measure Abs at 583nm
  • Rate of diffusion = Abs change over 5 mins


Sample Data collected 
Rate of diffusion measured by
  • Absorbance change over 5 mins
  • (Final Abs - Initial Abs) / 5mins
  • Beetroot in ethanol - Blank is ethanol
  • Beetroot in SDS - Blank is SDS
  • Assumption used - Initial Abs = 0
  • Diluted ethanol/SDS is prefer as they may affect the Abs reading





Video on beetroot diffusion measured using visible spectrophotometer

IA done by my student on beetroot experiment. A beautiful experiment. Try it and have fun.

IB Biology diffusion of beetroot pigment measured using visible spectrophotometer
May need to download to view as preview in slideshare is not clear.
Thanks to all pictures used for the above post

Thursday, October 20, 2011

IB Chemistry Biology IA on Vitamin C quantification using Iodometric Titration or UV spectrophotometer

IB Chemistry Biology on Vitamin C quantification using UV spectrophotometer at 266nm


1. Sodium oxalate (0.0056M) - dissolving 0.075g sodium oxalate in 100ml pH 5 buffer
2. Vit C (0.001M ), prepared by dissolving 0.018g of Vit C in 100ml sodium oxalate solution
3. Perform 2 fold dilution on 0.001M Vit C.
4. Add 1 ml Vit C into a quartz cuvette and 2ml of sodium oxalate ( as a stabiliser )
5. Leave for 10 mins
6. Prepare a blank with 1ml water and 2 ml ammonium oxalate
7. Set up UV spectrophotometer at 266nm and quantify.
Result shown below
Latest journal published in April, accurate way to quantify Vit C. 
Click HERE to view
* Oxalate solution used as  stabiliser and pH around 5 as both affect the stability of Vitamin  C


Short video on Vitamin C quantification using UV spectrophotometer
........................................................................................................................................................
Vitamin C quantification using iodometric titration
  • Potassium iodate as oxidising agent in burette
  • Potassium iodide as reducing agent , starch and vitamin C (reducing agent) in conical flask
  • End point is blue black colouration
  • Chemical equation below
  • KIO3 + 5KI + 6H+ --> 3I2 + 6K+ + 3H2O
  • 3C6H8O6 + 3I2  --> 3C6H6O6 + 6I- + 6H+
  • Mole ratio KIO3:Vitamin C = 1 :3




Video on Iodometric Titration for Vitamin C quantification


IA Research question for Chemistry/ Biology on Degradation/decomposition of Vit C

  • Effect of heavy metals salts like Pb2+or Cu2+ 
  • Effect of pH and temperature 
  • Duration and exposure to light or UV light
  • Aerobic or anaerobic degradation
  • Effect/presence of different sugar and oxidising agent 

IB Chemistry Biology t test, mean, uncertainty error, standard deviation, statistical analysis

Central value of a normal distribution curve for a set of data can be recorded as 
  • Mean
  • Mode
  • Median
Consider the following set of data collected 
  • 5, 6, 6, 6, 6, 7, 9
Average can be in the form of Mean, Mode or Median
  • Mean = ( 5 + 6 + 6 + 6 + 6 + 7 + 9 ) /7 = 6.42
  • Median = 6 ( middle number )
  • Mode = 6 ( most common )
  • Conclusion = Can use mean, median or mode if data cluster together (normal distribution)
Consider the following set of data collected
  • 1, 7, 8, 8, 8, 9, 9
Average can be in the form of Mean, Mode or Median
  • Mean = ( 1 + 7+ 8 + 8 +8 +9 +9 )/7 = 7.14
  • Median = 8
  • Mode = 8
  • Conclusion = 1 is an outlier, mean is not appropriate (not normal distribution)
Uncertainty or standard deviation measures the spread/variability of values from the mean
Uncertainty can the the form of
  • standard deviation (SD)
  • standard error (SE)
  • confidence interval (CI)
  • uncertainty ± error

    • High SD - High spread of data - High Uncertainty
    • Low SD - Small spead of data - High Certainty
    • Uncertainty can be expressed in SD, SE and CI if the data is normally distributed
    • Rate can be expressed = (Rate ±SD), (Rate ±SE), (Rate ±CI)





    .........................................................................................................................................................
    IA by two students on effect of Conc on Rate of reaction.
    How concentration of hydrochloric acid affect the rate of reaction?
    Data collected by student 1
    Uncertainty in Rate expressed as SD, SE and CI is small.
    Rate ±SD against Conc was plotted below
    • Error bar/ SD do not overlap
    • High certainty a line passes through error bar
    • Small SD - More precise and highly certain a linear relationship bet Rate and Conc
    • Conc increase - Rate increase
    • Significant different between rates at different concentration




    Data collected by student 2
    Uncertainty in Rate is High
    Rate ±SD against Conc was plotted below

    • Error bar as SD overlap
    • High Uncertainty how the line pass through error bar
    • High SD - Less certain on the relationship between Conc and Rate
    • As Conc increase rate may be constant
    • No significant diff bet rate at higher conc
    • Significant diff bet rate at lower conc

    Data from both student shown below
    Uncertainty/Error bar/SD will determine
    • Small SD - High Certainty - Error bar don't overlap - Significant diff bet rates at diff Conc
    • Small SD - Highly Certain about relationship bet Rate and Conc (Conc up - Rate up)
    • High SD - High Uncertainty - Error bar overlap - No significant diff bet rates at diff Conc
    • High SD - High Uncertainty about relationship bet Rate and Conc (Conc up - Rate constant)
    ...........................................................................................................................................................
    Notes on using statistical t test - Testing of significant difference between two means

    IB Biology statistical analysis, t test, significant difference, hypothesis testing and standard deviation
    .............................................................................................................................
    Good video using Excel for graphing/ error bar plotting



    All notes for the above post is summarised in powerpoint below.

    Thanks to all picture and video contributors use for the above post

    Monday, October 17, 2011

    IB Chemistry uncertainty error calculation for RMM, propagation of error and standard deviation

    Uncertainty Calculation for RMM of butane gas using ideal gas equation


    Uncertainty Calculation for RMM using Ideal Gas Equation.
    Ideal gas law equation,  PV = nRT

    P - absolute pressure of the gas in kPa
    V - volume in dm3
    n - number of moles
    T - absolute temperature.(Kelvin)
    R = gas constant, 8.314 J K-1 mol-1


    PV = nRT,     n = mass / RMM
    PV =  (mass/RMM) x RT 
    RMM = (mass x RT) / PV
    To determine RMM of gas - need to find out
    • average mass of gas
    • average volume of gas
    • temp - 296.05K and pressure - 101.760kPa
    Data collection by two students. Which is appropriate and correct?
    Data by student 1:
    Student 1 took average mass for 5 trials shown above
    • Average Mass for gas = Average mass (flask + gas) - Average mass (flask + air) + Mass air
    • Average Vol gas = Average vol of water = Average mass water (density water 1g -1cm3)
    Calculate the RMM of a gas, given
    Average mass gas = Average mass (flask + gas) - Average mass (flask + air) + Mass for air
    Average mass gas = (55.734 - 55.610 + 0.129) = 0.253g


    Average Vol gas = Average Vol of water = Average Mass water = 107.953g = 107.953cm3 = 0.10795dm3
    Results on how to determine mass of air is shown below
    RMM gas = (mass x RT) / PV 
    RMM gas =  (mass x R x T) / PV    average mass gas = 0.253    average vol gas = 0.10795dm3
    RMM gas =  ( 56.6 ±2.56%) converted to absolute uncertainty = (56.6 ±1.45)= (56.6±1.4)
    ....................................................................................................................................................
    Data by student 2
    Did not take average mass or volume of gas
    • Find mass, vol and calculate RMM for trial 1
    • Find mass, vol and calculate RMM for trial 2
    • Find mass, vol and calculate RMM for trial 3
    • Find mass, vol and calculate RMM for trial 4
    Calculated average RMM for 4 trials
    Average RMM = 53.943








    How to calculate uncertainty for average RMM?
    RMM 1=(54.998 ±0.1890) RMM 2= (54.775±0.1883) RMM= (52.766±0.1814) RMM=53.232±0.1830


    Wrong way to calculate uncertainty for RMM
    • NEVER take the average of uncertainty - (0.1890 + 0.1883 + 0.1814 + 0.1830)/4 = 0.1854
    • WRONG ANSWER = (53.943 ±0.1854) = (53.94±0.18)
    Right way to calculate uncertainty for RMM
    RMM 1=(54.998 ±0.1890) RMM 2= (54.775±0.1883) RMM= (52.766±0.1814) RMM=53.232±0.1830

    1st method using std deviation for 4 diff RMM = (53.943±1.109) = (53.94±1.11)
    Average RMM = (53.94±1.11)

    2nd method using Max/Min error 
    Max RMM = 54.998        Min RMM = 52.766
    Uncertainty RMM = (Max - Min )/number trials = (54.998 - 52.766)/4 = 0.558 

    Average RMM = (53.943±0.558) = (53.94±0.56)
    ..........................................................................................................................................................

    Which data is better and is there a better way to collect data.


    Student 1 
    • average mass and average vol
    • only 1 RMM is calculated
    Student 2
    • one mass and one vol to find RMM
    • average RMM is calculated



    Student should perform both ways using average mass and average vol and also average RMM.
    • Use student 1 method to collect average mass and average vol and find RMM
    • Perform expt 3 time (triplicate) to obtain 3 different RMM
    • Find the average RMM using student 2 method
    .........................................................................................................................................................
    Detail error analysis and propagation of error done by student 1


    .........................................................................................................................................................

      .............................................................................................................................
      Simple Experimental setup
      Determination of (RMM) of a gas ( Butane ) using ideal gas equation.
      Steps to follow
      1. Weigh a dry 100ml volumetric flask with stopper to 0.001g
      2. Remove stopper
      3. Fill it with CO2/butane gas with glass delivery tube, stopper it and reweigh
      4. Repeat step 2 and 3 until mass of flask is constant
      5. Fill the flask with water, insert a stopper, and reweigh it.
      Click Here for IA on DCP and CE
      Detail Experimental Setup
      Click Here to view detail procedure setup.
      Source from Chemistry SLSS website
      Click HERE for more sample ideal gas calculation
      Click HERE for more info on ideal gas equation
      Thanks to all pictures and souces used for the above post

      Sunday, October 16, 2011

      IB Chemistry uncertainty error calculation for rate of reaction and standard deviation

      IB Chemistry on error analysis, uncertainty error calculation and standard deviation for rate of reaction.


      Research Question - How changing %conc NaCI affect rate of reaction?
      Data collected by two students to compute rate and its uncertainty. Which is correct?
      Data by student 1-

      • 5 trials for conductivity measurement was done for each conc
      • No average conductivity was taken 
      • 5 different rates obtained for each conc















      Graph by student 1 - change of conductivity over time for all trials
      For 1% Conc - Rate for first 60s calculated by
      • mesuring slope for 5 trials
      • average rate was taken
      • (Rate 1 + Rate 2 + Rate 3 + Rate 4 + Rate 5)/5
      • ( 10.66±0.02 + 10.41±0.05 + 10.47±0.04 + 10.14±0.05 + 10.50±0.02 ) /5
        Average Rate = (10.43)
        How to calculate uncertainty for rate?



      Wrong way to compute rate and its uncertainty
      Average Rate = (10.43 ± Average Uncertainty)

      NEVER take the average uncertainty
      ± Uncertainty Rate = (0.02 + 0.05 + 0.04 + 0.05 +0.02)/5 = 0.03
      Average Rate = (10.43 ±0.03) WRONG!!!!!

      Correct way to compute rate and its uncertainty
      1st Method –
      Average Rate = (10.43 ± Std deviation )
      Average Rate = (10.43 ± 0.19)

      2nd Method –
      Average Rate =  10.43 ±[ (max rate – min rate)/number of trials]
      ± Uncertainty rate = (max rate – min rate)/ number of trials
                                        = (10.66 – 10.14)/5 = 0.10
      Average Rate = (10.43 ±0.10)
      ...............................................................................................................................................
      Data collected by student 2

      Rate = Average Conductivity change/time

      • Average conductivity and std dev was computed for 5 trials
      • For 1% - average conductivity was taken at different time
      • Rate is average conductivity/time
      • For 1% conc - only 1 curve and std deviation is plotted
      Graph by student 2 - Average conductivity over time was plotted
      Rate = Average conductivity /time
      • Rate for 1% = Average change of conductivity for first 60s
      • Average conductivity at 60s = (0.10±0.07)
      Rate for 1% -
      • Measure the slope/gradient for 1st 60s
      • Rate for 1% = 0.10/60 = 0.00167
      • Rate = 0.00167





      How to calculate uncertainty for rate?

      Calculating uncertainty for rate for first 60s
      1st method - using uncertainty from the slope
      • Rate = (0.00167±0.0012) using uncertainty of the slope

      Rate = (0.00167 ±0.0012)

      2nd method - using Max/Min error method
      Conductivity for 1% at 60s = (0.10 +0.07)
      • Rate = Conductivity change /60s = (0.10±0.07)/60
      • Rate = 0.10/60 = 0.00167
      Max Conductivity = 0.107            Min Conductivity = 0.03
      Max Uncertainty Rate = Max Conductivity/60 = 0.107/60 = 0.00178

      Min Uncertainty Rate = Min Conductivity/60 = 0.03/60 = 0.0005
      Rate = 0.00167±(0.00178 --0.0005)

      3rd Method - % Uncertainty method
      Conductivity for 1% at 60s = (0.10±0.07)
      • Rate = Conductivity change/60s 
      • Rate = (0.10±0.07)/60
      • Rate = 0.10/60 = 0.00167
      How to calculate uncertainty rate?








      Calculating uncertainty rate

      • % Uncertainty rate = % Uncertainty Conductivity
      • % Uncertainty Conductivity = (0.07/0.10) x 100% = 70%
      Rate = (0.00167±70%) convert to absolute - (70/100) x 0.00167 = 0.0011
      Rate = (0.00167±0.0011)
      .......................................................................................................................................................
      Difference between student 1 and student 2

      Student 1 data :
      For 1% conc – 5 rates was obtained
      ( 10.66±0.02 + 10.41±0.05 + 10.47±0.04 + 10.14±0.05 + 10.50±0.02 )
      ·         At 1% conc – 5 rates obtained from 5 trials
      ·         At 1% conc - 5 curves – 5 slopes was obtained
      ·         Average rate was calculated
      ·         Uncertainty rate is calculated using std deviation or max/min method
      ·         NEVER take average for uncertainty!
      Student 2 data:
      For 1% conc – 1 rate was obtained
      ·         At 1% conc – average conductivity was taken
      ·         At 1 % conc – 1 curve – 1 slope was taken
      ·         Rate was calculated form average change conductivity/time
      ·         Uncertainty rate is calculated using 3 methods shown above

      .....................................................................................................................................................
      Notes for the above post is summarise into slideshare:


      Thanks to Stephen Taylor for his data table format
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