Question

Consider the reaction: Li₂S(aq) + Co(NO₃)₂ (aq) à 2 LiNO₃ (aq) + CoS (s)

What is the mole-mole factor (written as a conversion factor) for each reactant to product CoS (s)?

Calculate the molar mass of each substance in the above chemical reaction.

If 4.2 g of Li2S are placed in a flask with excess Co(NO₃)₂, how many grams of CoS are expected? (This is theoretical yield)

The reagents in this reaction are aqueous solutions. If 20 mL of 0.25 M Co(NO₃)₂
are mixed with excess Li₂S solution, how many grams of CoS will be formed? How many moles of LiNO₃ are expected?

If 3 mL of 1.0 M Li₂S is mixed with 3 mL of 0.50 M Co(NO₃)₂, how many grams of CoS will be produced?

After the reaction is complete, there are 50 mL of 0.5 M LiNO₃ present. How much CoS (in grams) was also produced? (No information about the reactants is needed)

Answer 1

Co(NO3)2 + Li2S -------------> CoS + 2LiNO3
no of moles of Co(NO3)2   = molarity * volume in L
                          = 0.25*0.02   = 0.005 moles
1 mole of Co(NO3)2 react with Li2S to gives 1 mole of CoS
0.005 moles of Co(NO3)2 react with Li2S to gives 0.005 moles of CoS
mass of CoS = no of moles * gram molar mass
             = 0.005*91 = 0.455g
1 mole of Co(NO3)2 react with Li2S to gives 2 mole of LiNO3
0.005 moles of Co(NO3)2 react with Li2S to gives 2*0.005/1 =0.01 moles of LiNo3

no of moles of Li2S = molarity * volume in L
                     = 1*0.003 = 0.003 moles
no of moles of C0(NO3)2 = molarity * volume in L
                         = 0.5*0.003 = 0.0015 moles
1 mole of Co(NO3)2 react with 1 mole of Li2S
    Co(NO3)2 is limiting reactant
1 mole of Co(NO3)2 react with Li2S to gives 1 mole of CoS
0.0015 mole of Co(NO3)2 react with Li2S to gives 0.0015 moles of CoS
mass of CoS = no of moles * gram molar mass
              = 0.0015*91 = 0.1365g

no of moles of LiNO3 = molarity * volume in L
                       = 0.5*0.05 = 0.025 moles
LiNO3 : CoS   = 2:1
              = 0.025 :0.0125
no of moles of CoS = 0.0125 moles
mass of CoS = no of moles * gram molar mass
             = 0.0125*91 = 1.1375g