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Stoichiometry Lab

Discover the limiting reagent, calculate theoretical and actual yield, and apply dimensional analysis across real balanced equations. Adjust reagent masses and percent yield to see how stoichiometry governs what chemistry can produce.

Guided Experiment: Limiting Reagent Investigation

If you have 4 g of H2 and 32 g of O2, which reagent do you predict will run out first? What happens to the other reagent?

Write your hypothesis in the Lab Report panel, then click Next.

Mole Bar Chart

Reactant AReactant BProduct (theoretical)Excess remainingLimiting reagent

Controls

Mass of H₂ (Reactant A)4.0 g
1 g200 g
Mass of O₂ (Reactant B)32.0 g
1 g500 g
Percent Yield85%
0%100%

Results

Limiting Reagent
H₂
Excess Reagent
O₂
Moles of H₂
1.9841 mol
Moles of O₂
1.0000 mol
Theoretical Yield
35.744 g
Actual Yield
30.382 g
Percent Yield
85.0%
Excess O₂ Remaining
0.0079 mol (0.254 g)
Dimensional Analysis
4.00 g H2×1 mol2.016 g×2 mol H2O2 mol H2×18.015 g1 mol=35.744 g H2O4.00\,\text{g }H₂\times \frac{1\,\text{mol}}{2.016\,\text{g}}\times \frac{2\,\text{mol }H₂O}{2\,\text{mol }H₂}\times \frac{18.015\,\text{g}}{1\,\text{mol}}= 35.744\,\text{g }H₂O

Yield vs. Mass of Reactant A

Theoretical yieldActual yield (85%)Limiting reagent crossover

Data Table

(0 rows)
#TrialMass A(g)Mass B(g)LimitingTheoretical Yield(g)Actual Yield(g)% Yield(%)
0 / 500
0 / 500
0 / 500

Reference Guide

Stoichiometry

Stoichiometry uses balanced chemical equations to relate the amounts of reactants and products. The coefficients give mole ratios that must be respected in every calculation.

a A+b B→c Ca\,A + b\,B \rightarrow c\,C

To find grams of product C from grams of reactant A, convert grams to moles, apply the mole ratio c/a, then convert back to grams.

gA→÷MAnA→×c/anC→×MCgCg_A \xrightarrow{\div M_A} n_A \xrightarrow{\times c/a} n_C \xrightarrow{\times M_C} g_C

Limiting Reagent

The limiting reagent is the reactant that runs out first, stopping the reaction. The other reactant is in excess and has some left over.

To find the limiting reagent, compare the mole-to-coefficient ratios:

Limiting if nAa<nBb\text{Limiting if } \frac{n_A}{a} < \frac{n_B}{b}

The reagent with the smaller ratio is consumed first. All yield calculations must be based on the limiting reagent's moles.

Percent Yield

Theoretical yield is the maximum amount of product possible, calculated from the limiting reagent. Actual yield is what you collect in the lab.

% yield=actual yieldtheoretical yield×100\%\,\text{yield} = \frac{\text{actual yield}}{\text{theoretical yield}} \times 100

Percent yield is always between 0% and 100%. Common causes of low yield include incomplete reaction, side reactions, and physical transfer losses.

Dimensional Analysis

Dimensional analysis converts between units by multiplying by fractions equal to 1. Each step cancels the unwanted unit and introduces the desired one.

g×1 molMA g×c mol producta mol reactant×MC g1 molg \times \frac{1\,\text{mol}}{M_A\,\text{g}} \times \frac{c\,\text{mol product}}{a\,\text{mol reactant}} \times \frac{M_C\,\text{g}}{1\,\text{mol}}

This chain of unit conversions is the foundation of all stoichiometric calculations. Cancel units step-by-step to check your work.