Khan Academy- Dilution and Concentration Explained

What Dilution and Concentration Actually Mean

These aren't abstract concepts. Dilution means making a solution weaker by adding more solvent. Concentration means making a solution stronger by removing solvent or adding solute. That's it. Every chemistry student overcomplicates this.

Khan Academy breaks these down with video lessons and practice problems. The platform walks you through the math without the fluff. If you're stuck on homework or need a quick refresher, it's worth bookmarking.

The Formula Nobody Remembers Correctly

The dilution equation is C₁V₁ = C₂V₂. Students mix this up constantly. Here's what each variable means:

• C₁ = initial concentration (the stuff you start with)
• V₁ = initial volume (how much you start with)
• C₂ = final concentration (what you want)
• V₂ = final volume (what you need to end up with)

The rule: moles of solute stay constant. You're not adding or removing the actual substance—you're just changing how much solvent is in the mix.

How To Solve Dilution Problems in 4 Steps

Most textbook problems give you three values and ask for the fourth. Here's the process that actually works:

Step 1: Identify Your Variables

Write down C₁, V₁, C₂, and V₂ from the problem. If the problem uses percentages, convert to decimals first. 10% becomes 0.10. This trips people up constantly.

Step 2: Plug Into the Equation

Insert your known values into C₁V₁ = C₂V₂. Leave the unknown variable as x.

Step 3: Solve for the Unknown

Isolate your variable. Most problems require basic algebra. If you can't isolate variables, that's your actual problem—not the dilution concept.

Step 4: Check Your Units

Your answer needs to make sense. If you calculated 500 mL but started with 100 mL and diluted, something went wrong. Always verify.

Concentration Units Compared

Different fields use different units. Here's the breakdown:

Molarity is what you'll use most in introductory chemistry. Don't waste time memorizing all of them until you know which one your instructor expects.

Common Mistakes That Cost Points

• Forgetting to convert units. mL and L don't mix. Pick one and stick with it.
• Adding solute instead of solvent. Dilution means adding solvent. If you're adding more stuff, you're concentrating.
• Confusing C₁ and C₂. C₁ is always your starting solution. C₂ is always what you're making.
• Using the wrong formula. C₁V₁ = C₂V₂ only works when moles stay constant. It doesn't apply to reactions.

Where Khan Academy Fits In

The platform has dedicated videos on dilution and serial dilutions. The explanations are straightforward. Each video includes practice problems with solutions.

What works well: the step-by-step problem solving. What doesn't: sometimes the videos move too slow if you already grasp the basics. Speed up the playback if needed.

The key is actually doing the practice problems. Watching videos without practicing is useless. Chemistry requires repetition.

Serial Dilutions: When One Dilution Isn't Enough

Serial dilutions are just repeated dilutions. You take a portion of your diluted solution and dilute it again. Lab technicians use this for bacterial cultures, medical testing, and creating standard curves.

The math stacks. If you dilute 1:10 three times, your total dilution factor is 10³ or 1,000. Each step multiplies the previous dilution.

Quick Reference Cheat Sheet

• Dilution: add solvent → concentration decreases, volume increases
• Concentration: remove solvent or add solute → concentration increases, volume decreases
• Moles never change in a simple dilution
• Always check your units before calculating
• Serial dilutions multiply dilution factors

Bookmark this. Come back when you're stuck on a problem. The formula and steps above cover 90% of what you'll encounter in general chemistry.