Dilutions

An Introduction

Activity overview

• In this activity you will visualize what is meant by a ‘dilution’.

• You will also examine how to express the dilution that has been made.

Part I: Dilutions made with food coloring

The intensity of the blue color decreases because, as weprogress through the tubes in the series, the concentrationof the blue food coloring in the tube decreases….

Let’s determine what dilutions of food coloring were madein each tube….

Determination of dilutions

Dilution #Volume blue f.c.

(mL)Total Volume

(mL)Dilution

(fraction)

1 5 10 5/10 =1/2

2 5 15 5/15 = 1/3

3 2 10 2/10 = 1/5

4 1 10 1/10

The dilution made in each tube is expressedby the following ratio:

Volume of blue food coloring stockTotal volume of dilution*

*The total volume = Volume blue FC stock + Volume water

Part II: Dilution simulation with beads

Overview

In this part of the activity, you will visualize dilutionsby using colored beads as your red food coloring stock and clear beads as water.

You will also observe how the dilution made correlates with the concentration of the dilution…

Determination of the concentration of your red bead

stock…

• For your simulated red bead stock, concentration is defined as:

# red beadsvolume of red beads

Let’s determine what dilutions of red bead stock were madein each tube….

Determination of dilutions

Dilution #Vol red bead stock

(mL)Total Volume

(mL)Dilution

(fraction)

A 15 30 15/30 =1/2

B 5 25 5/25 = 1/5

Determination of concentrations of dilutions A

and BThe concentration of each dilution can be determined by physically counting the number of red beads ineach tube. Concentration is simply:

# red beadsTotal dilution volume

Dilution # red beadsTotal volume of

dilution (mL)Concentration(red beads/mL)

A 1790 30 60B 620 25 25