## How many drops of water can fit on a penny?Biology 4 - LidIa Orellana- 2/13/17 - #1.1

### Introduction

What we're trying to find is how many drops of water can fit on a penny. Our hypothesis was 8 drops of water can fit on the penny. We thought only 8 drops of water because a penny is small and we didn't think so much water would would fit on a penny,however; we were wrong. In this lab we experienced cohesion and surface tension. Surface tension allowed attraction between water molecules making them stick together by creating a bump when we added more drops of water. Not only surface tension allowed so many drops of water, but also cohesion. Cohesion is when alike molecules stick together and in this case it was water moleules that were put togehter because they were attracted to the same substance;water.

### Materials

For this lab we used: A penny, an eyedropper, soap, a cup of water, and paper towels.

### Procedures: Part A

First, we start by making a hypothesis of how many drops of water can fit on a penny. Next, we get the materials we need to complete this lab. We start by filling the paper cup half way with water. We get paper towels and place them on our station with the cup of water. Now we place the penny on top of the paper towels. We now start by taking the eyedroppers, filling it with water, and placing the drops of water on to the penny. We complete this four times, until the bump of water breaks completley, don't forget to count how many drops of water can fit every 4 trials. After, you've done the 4 trials, take the average of each.

### Procedures: Part B

For Part B you will need the same materials except you will add soap to the water. You will start with by dipping the clean penny into the water mixed with soap. After, you've done this you can proceed the same steps as Part A, just add the drops of water with soap to the penny.

### Results

Our hypothesis was way off, the average of Part A was 27.5. The trials went from 33,11,36,and 30. Trial 2, was the lowest of them all because it depends the force you are putting onto the eyepdroppers and how well your hand can maintain stability. Next, for Part B the average was 27.25. This average is less because soap reduces the cohesive force and breaks surface tension.

### Discussion

1.) Explain your results from both parts of the experiment in terms of cohesion and surface tension.

1.) On part A, cohesion came in play because water was the only substance we used, so the water molecules attracted one another due to the cohesion property; which is when alike molecules attract. Surface tension formed the bump around the penny when the water molecules were attracting to each other.

On part B, when soap was added to water the molecules didn't attract as much because it wasn't cohesion anymore. Then, the bump around the penny wasn't strong or big enough.

2.) How do your results compare to the other groups in your class?

2.) Our results were different from other groups, like some groups reached up to 50 or more drops . It all depends on how much force was used on the eyedroppers, on how quick or slow you were going, and if your hand was shaky or still.

### Conclusion

The purpose of this lab was to see the difference of how many drops of water can fit on a penny with and without soap. My partner and I found out that without soap the water molecules will attract eachother more due to cohesion and with soap they won't attract as much. The surface tension without soap was a stronger and bigger bump, but with soap it was the oppisite of that. We discovered that cohesion is when alike substances attract to one another and that surface tension is what allowed the bump around the penny to get larger. We learned that everybody will have different results and how cohesion and surface tension allowed the drops of water to go on the penny. Overall, if you want to try this lab take your time if you want to get a high number of drops as your result and make sure you understand how cohesion and surface tension came in play during this lab.

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