Rainbow in a Straw Lab - Weebly



Name(s)_______________________________ _______________________ Date _________________

Liquid Layers

Problem: Can you determine the different density of each liquid, and create a rainbow in a straw?

Background:

Define Matter: ___________________________________________________________________

Mass and volume are properties of matter.

Density is the ratio of mass and volume. The particular density of a specific kind of matter helps to identify it and distinguish it from other kinds of matter. Density is how we compare mass to volume.

The formula used to calculate density is

mass ÷ volume

In this lab you will first start by measuring the properties of 5 different liquids. These liquids are a combination of the compounds NaCL, H2O, and food coloring. What is the name of each element used in the liquid?

Na:_______________ Cl: _________________ H: __________________ O: ___________________

Please explain whether the liquids we are using in the lab are considered and substance or a mixture and why.

______________________________________________________________________________________________

If you classified the liquid as mixture, please explain in detail what type of mixture it is and why.

______________________________________________________________________________________________

Part One: Determine the density of each liquid.

Materials:

|5 liquids |Graduated cylinder |Triple Beam Balance |Calculator |Test Tubes with rack |

|Procedure: |

|Use the triple beam balance to find the mass your graduated cylinder. (empty) Record. |

|Add 25 ml of the first liquid. |

|Find the mass of the graduated cylinder + the liquid. Record. |

|Subtract. The mass of the graduated cylinder from the mass of the graduated cylinder + the liquid. |

|Record. |

|Calculate density. D = M/V |

|Pour liquid into the correct test tube. |

|Repeat for all liquids. |

Data Table 1

Data Analysis:

|Liquid |Mass of |Mass of |Mass of |Volume |Density |

| |Graduated cylinder |Graduated cylinder + |Liquid | | |

| | |liquid | | | |

|Liquid 1 | | | | | |

|Liquid 2 | | | | | |

|Liquid 3 | | | | | |

|Liquid 4 | | | | | |

|Liquid 5 | | | | | |

Graph your data using bar graph.

Title: ___________________________________________________________________

[pic]

|Things to remember before the lab! |

|How do we use a triple beam balance? |

|How do we measure from a graduated cylinder? |

|Handle all equipment with care!! |

|Test tube rack can fall apart… carry cautiously from the bottom |

|Test tubes and graduated cylinders are glass. Please be careful! They will break if dropped even a little bit.|

|All supplies will be returned at the end. Including the liquid samples. |

|Read ALL directions for the lab before performing the experiment. |

|Goggles and aprons at all times. |

|Misbehave and I remove you from the lab! |

1) Do all background work on the first page.

2) Follow all procedures very carefully on the bottom of the first page. Record all of your findings in the data table. Don’t forget to use your units (g, mL, and g/mL ). Next to the density of the liquids mark them #1-#5 with #1 being the least dense and #5 being the most dense.

3) Work with your group to create a graph that represents the collected data in the space for the graph. Don’t forget a good title, labels, and a key if needed!

Part Two: Creating a rainbow in a straw.

Using what you know about the density of the mystery liquids, you will create a rainbow in a straw.

Procedure:

1. Let’s practice the straw-dropper technique using the least dense liquid. Place one end of the straw into the liquid – about an inch – and place your index finger over the other end of the straw. Pull the straw out of the water and notice how the liquid stays in the straw. If you release your finger, the liquid will fall out of the straw. Make sure you can do this well before moving onto the next step.

2. Place the empty straw into the least dense liquid (a few centimeters below the surface). Seal the other end of the straw with your index finger and remove the straw. There should be about 2-3 cm of liquid in the straw. Keep your finger firmly pressed against the top so the water doesn’t fall out.

3. Without releasing your finger, lower the straw into the next denser liquid about a little lower than the other liquid in the straw. Slowly release your finger from the top of the straw and the second liquid will push the other layer up to the level of the water in the other cup. Press your finger firmly on top of the straw and remove the straw. Look… you have two layers! Don’t get so excited that you release your finger from the top of the straw – you’ll have to start all over again! Also, be sure to hold the straw straight up and down (vertically) because tilting the straw will cause the liquids to mix and you’ll have to start again.

4. Continue to repeat step 3 with all 5 liquids going from least dense to most dense. When you are done you should have a rainbow in your straw! Once you have the rainbow in your straw carefully turn it upside down and see what happens. Write your observations on the conclusion page.

5. All good things must come to an end. When it feels like your index finger is going to fall off, release the pressure and your masterpiece will fall into the remaining empty test tube.

6. Clean up your station (non mixed colors go back into the beaker, mixed colors into the sink. Answer the questions on the conclusion paper together as a group.

Conclusions:

What happened to the solution when you turned it upside down? Explain why this occurred.

______________________________________________________________________________________________

______________________________________________________________________________________________

______________________________________________________________________________________________

Why did the previous less dense liquid always rise in the straw when you added the next more dense liquid to it?

______________________________________________________________________________________________

______________________________________________________________________________________________

______________________________________________________________________________________________

What do you think would have happened if you would have stated your straw rainbow with the most dense liquid and then added more less dense liquids to the straw?

______________________________________________________________________________________________

______________________________________________________________________________________________

______________________________________________________________________________________________

If there were the exact same ingredients in each liquid mixture (salt (NaCl), water (H2O), and food coloring), how could each mixture have a different mass and therefore density? (Hint: How much of each ingredient was added to each solution?)

______________________________________________________________________________________________

______________________________________________________________________________________________

______________________________________________________________________________________________

Grading Rubrics

Name:

________________________

|Behavior throughout the | / 20 |

|lab | |

|Participation in group | /20 |

|Correct answers to lab | /40 |

|worksheets | |

|Clean up: nice, neat, | /20 |

|nothing broken | |

|Total Grade | /100 |

Name: ________________________

|Behavior throughout the | / 20 |

|lab | |

|Participation in group | /20 |

|Correct answers to lab | /40 |

|worksheets | |

|Clean up: nice, neat, | /20 |

|nothing broken | |

|Total Grade | /100 |

Name: ________________________

|Behavior throughout the | / 20 |

|lab | |

|Participation in group | /20 |

|Correct answers to lab | /40 |

|worksheets | |

|Clean up: nice, neat, | /20 |

|nothing broken | |

|Total Grade | /100 |

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