Limiting Reactants and Percentage Yield

Lab Brief #6

🎯 Your mission

Set it up. Test it. Be amazed.

⚡ The twist

Nature loves to surprise the careful watcher.

What you'll learn

The limiting reactant runs out first and caps how much product can form; the other is in excess. Real yields fall short of theoretical because of side reactions, losses in transfer and reversible steps. Percentage yield is actual divided by theoretical, times 100.

Key words

limiting reactant
The reactant that is used up first and so limits the product formed.
percentage yield
Actual yield divided by theoretical yield, expressed as a percentage.

Make a hypothesis first

Before you start: write down what you think will happen, and why.

Say your guess out loud — then find out if you were right.

Get ready

🧰 What you need

magnesium ribbon
dilute hydrochloric acid
conical flask
gas syringe
balance
measuring cylinder

Get ready

⚠️ Safety first

Dilute hydrochloric acid irritates eyes and skin — goggles on, rinse splashes at once.
Hydrogen is flammable: no flames anywhere in the room during this experiment.

Step 1 of 4 · Read

Think about what you just learned: say what "limiting reactant" and "percentage yield" mean in your own words before you start.

Step 2 of 4 · Do

React measured masses of magnesium with a fixed volume of dilute hydrochloric acid, increasing the magnesium each time. Plot hydrogen produced against magnesium added and identify where the acid becomes limiting.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 2

The limiting reactant is the one that:

How sure are you?😐 maybe

Question 2 of 2

A reaction predicted to give 8 g yields 6 g. The percentage yield is:

How sure are you?😐 maybe

Mind = blown

🔬 The more you look, the more nature shows you.

Nice work!

You got 0 of 2 right.

Next: Concentration of Solutions All lessons

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✨ More to explore

🌍 Where you see this in real life: This shows up in your everyday life more than you'd think.

🏆 Stretch challenge (try it this week): Try one experiment in real life this week — even a tiny one.

👨‍👩‍👧 For the dinner table: “What's the most surprising thing you learned today?”

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