Question 2 : Many chemical salts come as hydrated crystals, i.e. there is a specific ratio of water molecules associated with the salt crystals. For example: CaCl2. 2H2O (Calcium chloride dihydrate; FW = 147.01 g/mol) has 2 water molecules to every CaCl2 molecule. The difference between anhydrate and dihydate is that anhydrate form CaCl2 does not contain any water molecules whereas dihydrate form contains two H2O molecules per CaCl2 molecule. Therefore since it is possible to have CaCl2 as an anhydrous (without water) powder the molecular weight of the anhydrate is 36 g/mol lighter than the dihydrate form (FW = 110.98 g/mol). Once dissolved in water, these salts have the same chemical properties, but in the solid state they obviously have different FWs. You are given a recipe for a buffer that contains 8% (w/v) CaCl2.2H2O, however, you only have CaCl2 anhydrous available to you. How much CaCl2 anhydrous do you need to make 3.5 L of the buffer with the same molar concentration as in the recipe? Show your calculations.
Question 2 :
Many chemical salts come as hydrated crystals, i.e. there is a specific ratio of water molecules associated with the salt crystals. For example: CaCl2. 2H2O (Calcium chloride dihydrate; FW = 147.01 g/mol) has 2 water molecules to every CaCl2 molecule. The difference between anhydrate and dihydate is that anhydrate form CaCl2 does not contain any water molecules whereas dihydrate form contains two H2O molecules per CaCl2 molecule. Therefore since it is possible to have CaCl2 as an anhydrous (without water) powder the molecular weight of the anhydrate is 36 g/mol lighter than the dihydrate form (FW = 110.98 g/mol). Once dissolved in water, these salts have the same chemical properties, but in the solid state they obviously have different FWs. You are given a recipe for a buffer that contains 8% (w/v) CaCl2.2H2O, however, you only have CaCl2 anhydrous available to you. How much CaCl2 anhydrous do you need to make 3.5 L of the buffer with the same molar concentration as in the recipe? Show your calculations.
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