IMSO 2011 Science International – Experiment

**Editorial safety note, which takes priority over the historical instructions:** Work under adult/teacher supervision, protect your eyes, and do not taste any material. Inspect the graduated cylinder for cracks; handle the nail's sharp tip and all glass carefully. Lower objects gently without dropping, forcing or striking them against the cylinder. Stop and ask the teacher if an object will not fit or cannot be handled safely with the supplied equipment. Never collect broken glass by hand. Wipe spills promptly. Keep water, salt solution and oil waste in the separate labelled, covered containers, and give them to the teacher for locally appropriate disposal; do not pour oil down a drain or put loose liquids/broken glass into an ordinary trash bag. The source's trash-bag instruction below is retained for comparison, not as permission for unsafe disposal. Wash hands afterward. The source prints no measured volumes: record your own readings, and do not invent data.

### Experiment 1

### Introduction

Sometime around 250 BC, the Greek mathematician Archimedes was given the task of determining whether a craftsman had defrauded the King Hero I of Syracuse by replacing some of the gold in the King’s crown with silver. Archimedes thought about the problem while relaxing in a bath tub. As he entered the bath tub, he noticed that water spilled over the sides. He realized that the amount of water that spilled was equal in volume to the space that his body occupied. This fact suddenly provided him with a method for differentiating a mixed silver and gold crown from a pure gold crown. Because a measure of silver occupies more space than an equivalent measure of gold, Archimedes placed the craftsman’s crown and a pure gold crown of equivalent mass in two tubs of water. He found that more water spilled over the sides of the tub when the craftsman’s crown was submerged. It turned out that the craftsman had been defrauding the King! Legend has it that Archimedes was so excited about his discovery that he ran naked through the streets of Sicily shouting "Eureka! Eureka!" (the Greek word for "I have found it!").

Archimedes had used the concept of density to expose the fraud. Density is a physical property of matter that expresses a relationship of mass to volume. The more mass an object contains in a given space, the denser it is. In chemistry and physics, density is a key concept in analyzing how substances and materials interact in fluid mechanics, weather, geology, material sciences and engineering. In biology, density is important concept in population ecology as well as vegetation analysis.

So enjoy discovering and experimenting on the materials that are provided for you as you experience working on the density of several solid objects.

### List of Materials

Note: Please check if you have a complete set of materials for the experiment before you start.

1. graduated cylinder — 1 piece (50 mL)
2. different liquids in a bottle — water; salt solution
3. cooking oil — 1 sachet (50 mL)
4. glass marble — 1 piece
5. nut and bolt — 1 pair
6. concrete nail — 1 piece
7. trash bag — 1 piece
8. clean rug — 1 piece
9. plastic container with cover (for liquid disposal) — 3 pieces (water, oil and salt solution)

### Methods

Your primary objective for this experiment is to determine and compare the densities of the solids that are given to you. With the materials listed above at hand, perform your experiment by following the instructions below.

**A. Preparation of the Experimental Design**

1. Plan your experiment by thinking of a design based on the materials provided to you.
2. Write the experimental design in a flow chart form.
3. Draw your design on the box provided then label or describe your drawing opposite your drawing.

[Space for your flow chart, experimental drawing, labels and description: ____________________]

**B. Performing the Experiment**

Perform the experiment that you designed.

Note:
- Please be careful in performing the experiment to avoid breakages of glassware. Broken glassware will not be replaced.
- Dispose your liquids properly. You were provided with separate containers for the liquids and should be placed in the trash bag after the experiment.

**C. Writing your results**

Write your data by completing the tables below:

**1. Density of solids**

Table 1. Density of solids in water.

| Solid | Volume 1 (mL) | Volume 2 (mL) | Displaced Volume (mL) | Mass of Solid (g) | Density of Object (g/mL) |
| --- | --- | --- | --- | --- | --- |
| glass marble | | | | 5.74 | |
| nut and bolt | | | | 24.14 | |
| nail | | | | 6.13 | |

Table 2. Density of solids in salt solution.

| Solid | Volume 1 (mL) | Volume 2 (mL) | Displaced Volume (mL) | Mass of Solid (g) | Density of Object (g/mL) |
| --- | --- | --- | --- | --- | --- |
| glass marble | | | | 5.74 | |
| nut and bolt | | | | 24.14 | |
| nail | | | | 6.13 | |

Table 3. Density of solids in oil.

| Solid | Volume 1 (mL) | Volume 2 (mL) | Displaced Volume (mL) | Mass of Solid (g) | Density of Object (g/mL) |
| --- | --- | --- | --- | --- | --- |
| glass marble | | | | 5.74 | |
| nut and bolt | | | | 24.14 | |
| nail | | | | 6.13 | |

A. Plot a graph of the density of object against the kind of liquid used to measure its density. Use a separate graph for each solid given.

[Three graphs: ____________________]

B. Based on your graphs, does the density of an object differ when measured using different liquids? Explain your answer.

[Answer: ____________________]

C. Based on the experiment, what were the important factors in determining the density of a solid?

[Answer: ____________________]

**2. Determining the mass of the displaced liquid**

Since the density expresses a relationship of mass to volume, the volume of the object can be computed from its mass and density. A relationship between the volume of the solid and that of the displaced liquid can be expressed as:

$$\frac{m_1}{D_1}=\frac{m_2}{D_2}$$

where:
- $m_1$ = mass of the object
- $m_2$ = mass of the displaced liquid
- $D_1$ = density of the object
- $D_2$ = density of the liquid

| Liquid | Displaced Volume (mL) | Mass of Glass Marble (g) | Density of Object (g/mL) | Density of Liquid (g/mL) | Mass of Displaced Liquid (g) |
| --- | --- | --- | --- | --- | --- |
| water | | | | 0.99 | |
| salt solution | | | | 1.07 | |
| oil | | | | 0.89 | |

a. How were you able to determine the mass of the displaced liquid? Write your formula on the blank provided in your answer sheet.

[Formula: ____________________]

b. What is the importance of using the above method in determining the mass of the displaced liquid?

[Answer: ____________________]

**D. Conclusion**

After conducting your experiment, write your conclusion/s on the space provided in your answer sheet.

[Conclusion(s): ____________________]

**Editorial safety override and missing materials:** Do not carry out the source instruction to blow talcum powder. Do not inhale or disperse talc or detergent dust. An adult/teacher must handle any powder in a way that prevents airborne dust; if this cannot be assured, use a teacher-provided demonstration/recording instead. Keep your face away, protect eyes, avoid skin/eye contact, do not taste any material, and wash hands afterward. Use a stable tray, handle spills promptly, and let the teacher collect the oil/detergent mixture for appropriate disposal; do not pour oil down a drain. Detergent is required in step 6 but missing from the source materials list. Step 5 also requires a way to measure 5 mL; an uncalibrated dropper does not establish this volume. The teacher must supply suitable detergent and a calibrated measure, and approve safe quantities, before proceeding. Keep the original wording below for source fidelity, but follow this safety override.

**Editorial scientific caution:** This is an oil–water surface demonstration, not a functioning cell membrane. The source questions contain oversimplifications. Record genuine observations and distinguish them from the membrane analogy; scientifically justified corrections are accepted.

### Experiment 2

### Introduction

The cell, the most basic organization of every living thing is covered by a cell membrane. This membrane keeps all of the pieces inside as well as protects every cell as it chooses the substances that can come into the cell. Compounds called proteins and phospholipids make up most of the cell membrane.

Scientists describe the organization of the phospholipids and proteins with the model called the fluid mosaic model. That model shows that the phospholipids are in a shape like a head and a tail. The heads like water (hydrophilic) and the tails do not like water (hydrophobic). The tails bump up against each other and the heads are out facing the watery area surrounding the cell. The two layers of the membrane is called the lipid bilayer.



[Editorial Vietnamese label glossary is provided after the procedure; the original image is retained intact.]

In the following experiment, you will have an opportunity to observe hydrophobic and hydrophilic substances and how they actually react with water and other substances. In this activity, you can observe how the cell membrane behaves when substances comes into contact with it, thereby choosing what kinds of substances can enter the cell.

### List of Materials

Please check if you have complete set of the following materials:

1. shallow plastic container with cover — 1 piece
2. water — 1 bottle
3. talcum powder — 1 sachet
4. medicine dropper — 1 piece
5. cooking oil — 1 sachet
6. wooden stick (for stirring) — 1 piece

### Methods

1. Fill the plastic container almost up to the brim with water.
2. Sprinkle the talcum powder on the surface of the water. Once the water surface is entirely covered, gently blow away the excess powder.

**Safety override for step 2: do not blow; only adult-controlled, dust-preventing handling is allowed, or use a teacher-provided demonstration/recording.**


**3.** Using the medicine dropper, carefully put 5 drops of oil on the water. The area covered by the spreading film will be more or less circular in the shape when done with care.

**4.** In the same container, add 5 more drops of oil and observe what happen to the oil added at each drop. Record the results.

**5.** Add 5 mL more of oil in the same container. Using the wooden stick, stir the oil in the container and observe. Let the mixture stand for about 10 minutes and observe again. Record your observations.

**6.** Add a pinch of detergent powder to the mixture and observe what happens to oil. Record the results.

[Record actual observations for each stage, including each of the five added drops, immediately after stirring, after about 10 minutes, and after detergent. Blank response spaces are provided below; these are editorial recording aids, not supplied experimental results.]

| Stage | Your observations |
| --- | --- |
| Initial 5 oil drops | |
| Additional drop 1 | |
| Additional drop 2 | |
| Additional drop 3 | |
| Additional drop 4 | |
| Additional drop 5 | |
| After adding 5 mL oil and stirring | |
| After standing about 10 minutes | |
| After detergent | |

### Discussion of Results

Discuss your results by answering the following questions:

1. Which among the talcum powder and oil is hydrophobic and which is hydrophilic?
2. In the fluid mosaic model of the cell membrane, which part shall allow the entrance of the talcum powder, and which part shall allow the entrance of the oil molecules?
3. In your observation of the reaction of the detergent with the oil, what part of the cell membrane model can you liken the action of the detergent?
4. Considering all your observations, write your conclusion on the blank provided in your answer sheets.

[Answers 1–4 and conclusion: ____________________]

**Editorial glossary for the unchanged source image:** extracellular fluid (water environment) = dịch ngoại bào (môi trường nước); phospholipid = phospholipid; hydrophilic heads = các đầu ưa nước; hydrophobic tails = các đuôi kị nước; bilayer = lớp kép; cytoplasm (water environment) = tế bào chất (môi trường nước).