Column of Colored Salt Water

Essential Question
How does salinity affect density? Do different levels of salinity mix together when they are stacked on top of one another?

Objectives

 * Interpret qualitative results based on setup of an experiment and background information.

Introduction & Student Background
In this activity, students will demonstrate how density works with salinity by creating a column of different layers of water. The water will remain separate because of the varying levels of salinity.

Materials

 * Clear straws
 * 3 ounce paper cups
 * salt
 * water

PREP

 * 1) Put the same amount of water in each of the four cups.
 * 2) In Cup 1, add yellow food color but no salt. In Cup 2, add blue food color and one teaspoon of salt. Stir to dissolve. In Cup 3, add red food color and two teaspoons of salt. In Cup 4, add green food color and three teaspoons of salt.

ACTIVITY

 * 1) Dip the straw 1/4 inch into the cup of yellow water.
 * 2) Put your finger over the end of the straw, sealing it. Pull the straw out. The liquid should be stuck to the end of the straw so long as your finger seals the top end.
 * 3) Dip the straw 1/2 inch into the blue liquid.
 * 4) Remove your finger. The blue liquid should rush into the straw, pushing the yellow liquid higher and leaving the blue at the bottom end of the straw.
 * 5) Put your finger over the straw again and remove the straw from the cup. There should now be two layers.
 * 6) Dip the straw 3/4 inch into the red liquid, remove your finger, replace your finger, and pull the straw out. There should now be three layers - yellow, blue, and red.
 * 7) Put the straw 1 inch into the green liquid, remove and then replace your finger, and pull the straw out. There should be four layers in the end of the straw.

How it Fits to Standard

 * Carry out investigations by using instruments, observing, recording, and drawing evidence-based conclusions.
 * Answer questions by explaining observations of the natural world

Follow Up
TBW