Answer to Question #179303 in General Chemistry for chancee R kaiser

Question

if 4.10 grams of chromium is heated with 9.30 grams of chlorine what mass of chromium(III) chloride will be produced

Answer 1

2Cr + 3Cl₂ $\to$ 2CrCl₃.

So 2 moles of Cr react with 3 moles of Cl₂ . What do these quantities weigh? You need the molar mass of each. If Cr = 52 and Cl=35.5, then 1 mole Cr has a mass of 52g and 1mole of Cl₂ = 71g. So based on the stoichiometry 2 x 52g of Cr react with 3 x 71g of Cl₂ and make 2 x (52 +35.5x3)g of CrCl₃

104g Cr reacts with 213g of Cl₂ and make 317g of CrCl₃

Now look at the quantities you have. 4.1 grams of chromium is heated with 9.3 grams of chlorine. Find the proportionate mass of Cl₂ that would react with 4.1g of Cr.

104g Cr reacts with 213g of Cl₂, so 4.1g Cr would react with (213/104) x 4.1 = 8.4g of Cl₂ . You have 9.3 g of Cl₂ which is more than enough. So Cl₂ is in excess and only 8.4g of it can react leaving 9.3-8.4g unused. The limiting reactant is Cr and this will determine the mass of CrCl₃ made.

2 mole Cr makes 2 moles CrCl₃, so 104g Cr will make 317g of CrCl₃, therefore 4.1g of Cr will make (317/104) x 4.1 = 12.5g of CrCl₃