Question

The synthesis of urea by Frederich Wöhler in 1825 began the decline of the idea that "organic" chemicals could only be made by living organisms as part of their biological processes.

AgOCN(aq) + NH4Cl(aq) → AgCl(s) + NH2CONH2(aq)

If you perform this reaction and collect the following table of data, in which trial(s) is NH4Cl clearly the limiting reactant?

Trial mL AgOCN mL NH4Cl mass AgCl
1 10.4 mL 100.0 mL 4.9 g
2 20.2 mL 98.9 mL 10.1 g
3 30.0 mL 101.1 mL 20.6 g
4 40.2 mL 99.8 mL 30.2 g
5 50.1 mL 100.5 mL 30.1 g
6 60.2 mL 100.3 mL 30.2 g

The mL of AgOCN and NH4Cl are the initial amounts used, the mass of AgCl is how much was recovered from the reaction. (Hint: You do not need to do any calculations to answer this question.)

Answer 1

Look at the numbers (and we don't even know the concn AgOCN) although I assume it is constant from trial to trial. And I note the amount of NH4Cl is almost the same from trial to trial.
Trial 1 gives 4.9 g
Trial 2. more AgOCN gives more AgCl.
#3. more AgOCN gives more AgCl.
#4. more AgOCN gives more AgCl.
#5 and #6. more AgOCN does NOT give more AgCl so #5 and #6 must have NH4Cl as the limiting reagent. Right? #4 could have but we would need the concns of AgOCN and NH4Cl and make a calculation.