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Unit: Stoichiometry Lesson: #10 Topics:

The Solvay Process: A Case Study

 Many important involve chemical reactions that are difficult to perform and still be economically feasible.

 In some cases, the overall process must follow a series of reaction steps.

is a chemical that is needed in large amounts – it is used in the production of and .

 Historically, sodium carbonate was produced by burning plants or and mixing the ashes with water

 This method was both inefficient and very expensive because of the large amount of material that needed to be burned.

 The Solvay process was developed as a cost effective alternative. It involves a series of reaction steps and has a net reaction of: CaCO3 (s) + 2 NaCl (aq)  Na2CO3 (aq) + CaCl2 (aq)

 A net reaction is determined by looking at the various reaction steps and eliminating any chemical that appears as both a reactant and a product in the various steps. These chemicals are known as intermediates.

 Step 1: () is decomposed by heat to form (lime) and dioxide.

CaCO3 (s)  CaO (s) + CO2 (g)

 Step 2: Carbon dioxide reacts with aqueous and water to form aqueous ammonium hydrogen carbonate.

CO2 (g) + NH3 (aq) + H2O (l)  NH4HCO3 (aq)

 Step 3: The aqueous ammonium hydrogen carbonate reacts with to produce and solid baking soda.

NH4HCO3 (aq) + NaCl (aq)  NH4Cl (aq) + NaHCO3 (s)

 Step 4: The baking soda is heated up and decomposed into sodium carbonate, water vapor and carbon dioxide.

2 NaHCO3 (s)  Na2CO3 (s) + H2O (g) + CO2 (g)

 Step 5: The lime that was produced in the first step is mixed with water to produce slaked lime (calcium ).

CaO (s) + H2O (l)  Ca(OH)2 (s)

 Step 6: The slaked lime is added to the ammonium chloride produced in the third step to produce ammonia, and water.

Ca(OH)2 (s) + 2 NH4Cl (aq)  2 NH3 (aq) + CaCl2 (aq) + 2 H2O (l)

 Net Reaction):

CaCO3 (s) + 2 NaCl (aq)  Na2CO3 (s) + CaCl2 (aq)

 The two raw materials used up in the Solvay process (calcium carbonate and sodium chloride) are abundantly available and very cheap.

 The primary product is the sodium carbonate.

 A by-product is the calcium chloride which can be sold as a dessicant or as road to melt ice.

 The baking soda made in step 3 can also be sold as a byproduct but this limits the amount of sodium carbonate that can be produced.

Homework:  See accompanying sheet.

Chem 20 Stoichiometry and the Solvay Process

Use a above balanced equation to answer each of the following questions.

1. What mass of lime (see step 1 for names) can be produced by the decomposition of 400 kg of limestone in step 1 of the Solvay process? m = 224 kg

2. What volume of 1.45 mol/L ammonia would be required to produce 275 kg of ammonium hydrogen carbonate in step 2 of the Solvay process? V = 2.40 X 103 L

3. What volume of 0.75 mol/L sodium chloride would be required to react with 350 kg of ammonium hydrogen carbonate in step 3 of the Solvay process? V = 5.9 X 103 L

4. What volume of carbon dioxide gas will be generated at SATP by the decomposition of 180 kg of sodium hydrogen carbonate in step 4 of the Solvay process? V = 2.66 X 104 L

5. What mass of water is required to react with lime in step 5 of the Solvay process in order to produce 370 kg of slaked lime? m = 90.0 kg

6. Calculate the concentration of ammonium chloride if 87 kL is required to react with 190 kg of slaked lime in step 6 of the Solvay process. C = 0.059 mol/L

7. What mass of sodium carbonate can be produced during the Solvay process if 250 kg of calcium carbonate is allowed to react with 3000 L of 1.72 mol/L sodium chloride (refer to the net reaction equation)? m = 265 kg