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Analysis of Soda Ash

Analysis of Soda Ash . Hand in: Pre-Lab and Open Acetic Acid spreadsheet Today: Determine the amount of Na 2 CO 3 in a sample of Soda Ash Soda Ash is made up of Na 2 CO 3 and other stuff

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Analysis of Soda Ash

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  1. Analysis of Soda Ash • Hand in: Pre-Lab and Open Acetic Acid spreadsheet • Today: Determine the amount of Na2CO3 in a sample of Soda Ash • Soda Ash is made up of Na2CO3 and other stuff • We can use the fact that Na2CO3 is a base that will react with standardized HCl to calculate % in the original Ash sample: • 2 HCl (aq) + Na2CO3 (aq) → 2NaCl (aq) + H2CO3

  2. Analysis of Soda Ash • 2 HCl + Na2CO3 → 2NaCl + H2CO3 • Is actually a two-step process: • H+ + CO3-2 (aq) →HCO3- (step 1) • And then • H+ + HCO3- → H2CO3 (step 2) • So when you titrate: you will see two plateaus and two inflection points • Today, we will determine the 2nd endpoint to determine how much HCl is required to completely titrate all the Na2CO3

  3. HCO3-→ H+ + CO32- Ka2 = 4.7 x 10-11 H2CO3 → H+ + HCO3- Ka1 = 4.5 x 10-7

  4. Analysis of Soda Ash • So Today: • Set up Excel with active titration graph – use similar format as last week: • Column A – mL of HCl • Column B is pH • Column C is derivative • Set up Apparatus Similar to last week including: • ring stand, magnetic stirrer, burette holder, burette, pH meter, magnetic stir bar. • Acid (HCl) goes in burette • soda ash (about .2 grams) goes in beaker (WRITE VIAL # on data sheet as soon as you begin) • add 3-4 drops of methyl orange indicator • Calibrate the pH meter probe with 7 & 4 buffers

  5. Analysis of Soda Ash • Use Indicator Methyl Orange [Yellow(5), Red(3)] to help with the endpoint – see examples for color change to expect • You will ultimately do 5-6 titrations of the soda ash (enough in the vial) • Trial 0 • Add HCl carefully in order to graph 2 plateaus and find the 2nd endpoint • Determine the pH at the endpoint • Trails 1-4 or 5 • Simply titrate to THAT pH at the 2nd equivalence point • Record the volume of HCl to reach that pH • May want to do One or Two titrations to find EXACT pH at 2nd Equivalence Point • At least four titrations to get %Na2CO3 • “Save as” with different file names for first titration curve(s)

  6. Analysis of Soda Ash

  7. Calculations 2 HCl + Na2CO3→ H2CO3 + 2 NaCl SIMILAR TO PRE-LAB QUESTION #2 .108 moles

  8. Lab Report Due next Lab Period • Title Page • Purpose • Results - One Titration/Derivative Graph - Data Sheet (with sample calculations) - Present/Staple in order data/calculations were obtained/performed - Significant Figures and Units - Precision and Accuracy (the vials have true values you will be graded against) • Conclusion [ Errors , Improvements ] • Individual Checked-Pre-labs

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