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What Is Left Over

Part of the Stoichiometry section of Coddy's Chemistry journey. Lesson 26 of 41.

The reactant that does not run out is in excess: part of it reacts, and the rest is left at the end, mixed with the product.

Three steps: from the limiting reactant and the ratio, find the moles of excess that react; subtract them from the moles at the start; turn the moles left into grams if asked.

Three bars for hydrogen: 3 mol at the start, 2 mol react, 1 mol is left over

Hydrogen in excess: 3 mol at the start, 2 react, 1 is left

2H₂ + O₂ → 2H₂O with 3 mol H₂ and 1 mol O₂: 1 mol O₂ uses 2 mol H₂, so 1 mol H₂ (2 g) is left.

Challenge

Chips of calcium carbonate, $10.0\ \mathrm{g}$ , are dropped into $100\ \mathrm{mL}$ of $1.0\ \mathrm{M}$ hydrochloric acid: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. The fizzing stops. What mass of calcium carbonate is left?

Try it yourself

Physics diagram: balance, beaker

Solve for $m_{left}$

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Stoichiometry

1The Mole

Counting Particles: the Mole Avogadro's Number Molar Mass Mass, Moles and Particles Moles in a Formula Recap - Mole Bridge

4Equations and Mole Ratios

Balancing Equations Reading an Equation in Moles Mass to Mass Gas Volumes in Reactions Reactions in Solution Precipitation Recap - Rocket Fuel

2Gases

Molar Volume of a Gas Avogadro's Law Pressure, Volume, Temperature The Ideal Gas Law Recap - Weather Balloon

5Limiting Reactant

The Limiting ReactantWhat Is Left OverIndustrial Scale Recap - Aluminum Plant

3Solutions

Molar Concentration Preparing a Solution Ions in Solution Ion Concentrations Dilution Recap - Lab Prep

6Practice Problems

Recap - Fertilizer Plant Recap - Acid for the Plant Recap - Gases for Ammonia Recap - Ions in the Sample Recap - The Full Plant Recap - Bromide in Brine Recap - Chlorine for Bromine Recap - Magnesium Bromide Recap - Silver Bromide Test Recap - Balloon at Launch Recap - Balloon High Up Recap - Before It Bursts Recap - Hydrogen from Water