384 Views

Download Presentation
##### Titration of Sodium Carbonate

**An Image/Link below is provided (as is) to download presentation**

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -

**Carbonate Chemistry**• CO2 in atmosphere and dissolved in water • Major global buffering system • Industrial sources • limestone: CaCO3(s) + heat CaO(s) + CO2(g) • trona (Na2CO3) deposits Air/Water Equilibrium Ionization in Water**Titration of Na2CO3 with HCl**Step 1: Na2CO3 + HCl NaHCO3 + NaCl Step 2: NaHCO3 + HCl H2CO3 + NaCl Overall: Na2CO3 + 2HCl H2CO3 + 2NaCl At Ve1: Phenolphthalein pH At Ve2: BCG Ve2 Ve1 Equivalents of HCl added**Derivative Plots**Derivative plots can be used for accurate location of the equivalence point Raw data Spreadsheet First and Second Derivative Plots Click on “Derivative Plots” tab Raw data: pH vs V 1st derivative: d(pH)/dV 2nd derivative: d2(pH)/(dV)2 2nd derivative**Determination of Carbonate in a Sample**A 1.2040-g sample containing sodium carbonate and inert material was dissolved in water and titrated to the bromcresol green end point, requiring 32.50 mL of 0.1020 M HCl. Calculate the % Na2CO3 in the sample. For the BCG endpoint, the reaction is Na2CO3 + 2HCl H2CO3 + 2NaCl % Na2CO3 = 14.59%**Effects of Carbonate Equilibria on Titration of Carbonate**Shift in Phenolphthalein Endpoint Boiling to Enhance Second Endpoint**Effect of Absorbed CO2 on Titration of Na2CO3 with HCl**Ve1 Ve2 • Ve1 decreases • Ve2 is not affected • Use Ve2 for calculations Before After CO2(g) + H2O(l) + CO32(aq) 2HCO3(aq)**Boiling to Enhance Visual Endpoint in Titration of Na2CO3**with HCl • Na2CO3 + 2HCl H2CO3 + 2NaCl NaHCO3 Boiling removes H2CO3 as gaseous CO2 NaHCO3 + H2CO3 H2CO3(aq) CO2(g) + H2O**Summary: Titration of Sodium Carbonate**• Titration of Na2CO3 with strong acid yields two equivalence points • At phenolphthalein end point • Na2CO3 NaHCO3 • At bromcresol green (or methyl red) end point • All carbonate is converted to H2CO3 • pH of carbonate solutions may be unstable due to exchange of CO2 with atmosphere.