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Properties of Water - Lab

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Alaa Mashal

on 16 September 2013

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Transcript of Properties of Water - Lab

Submitted By:
Alaa Mashal, Alex Ganea, Gracie Pramono, and Gursimran Virk

Submitted To:
Mr. Westbury

Monday September 16, 2013

Course Code:
SBI4U - 04
The existence of water is essential for life on Earth; it covers up to 70% of the Earth's surface. Water is made up of two elements; hydrogen and oxygen. H2O has unique properties that allow it to be vital for life. Many of its properties include being odourless, tasteless, colourless and having a pH level of 7. Furthermore, water is used in our daily lives as most of our tasks involve using this substance. We use water for drinking, cooking, cleaning and much more. H2O is extremely important in our lives and without it we cannot survive.
Part One: Cohesion
- Quarter - Water
- Eye Dropper - Graduated Cylinder
1. Using a dropper count how many drops it takes to get 1 mL in the graduated cylinder.
2. Record the number of drops from your dropper it takes to produce 1cc of water, and the amount of water per drop.
Answer: It takes 19 drops from the dropper to produce 1mL of water.
19 # of drops = 1cc
1 drop = 0.0526 cc

3. Predict of how many cc's fit on the surface of a quarter.
4. Carefully squeeze droplets of water onto the quarter. Count up until the point of the quarter overflows. Record the number of drops.
Number of drops to fit on a penny: 35 drops
A quarter holds 1.84 cc's of water.
Our prediction was close to the actual result but not the same because we assumed the quarter to be smaller than it actually was. The quarter had a lot of surface tension due to the all the designs and ridges on the "heads" side. The surface tension that was built up caused a lip to form on the top of the quarter. The lip was in a dome shape and all the water kept getting collected due to cohesion. The water molecules at the surface of the quarter crowded together, producing strong layers as they are pulled downward by the attraction of other water molecules beneath them. We did not take the lip into account and that is a major reason why our prediction was a bit off.
6. Put a small dab of detergent on your finger and rub it on the surface of the quarter. How many droplets of water can the quarter hold until it overflows?

Number of drops to fit on a quarter with detergent: 23 drops.
A quarter that has detergent applied to it holds 1.210 cc's of water.
Part Two: Adhesion
- Quarter - Water
- Eye Dropper - Glass Slide
- Wax Paper
After 3 drops . . .
After 19 drops it hit the 1 mL line.
After 20 Drops . . .
Overflows after 35 Drops
After 1 Drop . . .
After 10 Drops . . .
After 1 Drop . . .
It overflows after 23 drops.
After 3 Drops . . .
1. Predict the shape of water droplets placed on a quarter, glass slide and wax paper by drawing the droplets.

Rough Sketches . . .
2. Carefully drop an equal number of droplets onto each surface medium and record the results.

Our prediction was that the quarter would hold less water because the detergent would decrease resistance for a lip to form and we were correct. The detergent prevented cohesion between the water molecules. Detergent is hydrophobic so it caused each water molecule to spread apart as the intermolecular forces of water were weakened. This caused less surface tension so the water was not able to form a lip but rather spread over the quarter and overflow.
Results ...

Wax Paper
Glass Slide
Person One
Person Two
Person Three
Person Four
Our predictions were quite accurate to the final results; however we were a bit hesitant about the wax paper. From the first experiment we discovered that the first drop of water on the quarter did not spread much but rather stayed in its place due to cohesion. So, we predicted that the first drop of water would be of medium size. When we conducted the experiment we were correct as the water drops began to form a lip again instead of spreading everywhere. Our prediction for the glass slide was that the water drop would expand as the glass slide has no tension for cohesion to take place. Our prediction was correct because when we conducted the experiment, the water drops began to spread around the entire slide. Our prediction for the wax paper was off by a bit as we thought that the wax paper would hold a large drop of water as it is adhesive. However, this was not the case. When the experiment was conducted, we saw that the water drop covered a small amount of space and formed a ball like shape that would roll off when the paper was tilted. Due to cohesion, the water droplets created a small ball of water, but there is still some adhesive force because some water was still left on the wax paper. There is some sort of attraction between the wax and water but not as strong as water-to-water and that is why the waterball rolls off and some stays behind on the wax paper.
Part Three: Solvency

- Water - Filter Paper
- Graduated Cylinder - Overhead Marker
- Stopwatch - Tape
- Pencil or pen - Scissors
1. Predict the time it will take water to creep up a strip of filter paper 2.5 cm wide?
We predict it will take about 10 - 15 minutes for the water to creep up the strip of filter paper
2. Trim one end of your filter paper so that it ends in a triangular point.
3. Obtain a 50 mL graduated cylinder, and using the pen and tape attach the squared end of the paper to the pen so that the paper "hangs" down with the tip just touching the bottom of the graduated cylinder.
4. Remove the paper and carefully make a solid dot with the marker at the point shown below.
5. Place 5 mL of water into the graduated cylinder. Place the paper carefully into the cylinder. Start the timer the moment the paper tip touches the water.
6. Note and record the time for 0min, 5min, 10min, 15 min and 20min.
5. Place 5 mL of water into the graduated cylinder. Place the paper carefully into the cylinder. Start the timer the moment the paper tip touches the water.
At 0 Minutes . . .
At 5 Minutes . . .
At 10 Minutes . . .
At 20 Minutes . . .
At 15 Minutes . . .
We predicted that the water would travel up the paper quickly at first and then slow down shortly afterward. Upon completing the experiment, we saw that our prediction was correct. In the first five minutes, the water had reached seven centimeters on the graduated cylinder from the original two centimeters that it started at. Once it reached the ten minute mark, the water was at eight and a half centimeters up the paper which means that it decreased in speed. After that it stabilized and moved up about two to two and a half centimeters every five minutes. Our prediction was accurate because the water went really fast up the paper in the first five minutes and then it started to slow down. When we took the paper out of the graduated cylinder we noticed that the water had made it's way up until it had reached twelve centimeters in twenty minutes.
Discussion Questions
1. If oxygen and hydrogen had equal electronegativity, the effect on the properties of water molecules would be that it would no longer be considered “sticky" or cohesive. Since oxygen has a higher electronegativity charge to hydrogen (2.5 – 2.1) it has the strength to pull in electrons from the hydrogen. The partial negative charge on oxygen attracts the partial positive charges on the hydrogen. If the two electronegativities were the same then the partial negative and partial positive charges would not form. The forming of those two charges is important because it give the molecule a dipole-dipole attraction or in other words, it would not form a hydrogen bond that causes the "sticky" aspect to water.

2. Detergents act as cleaning agents because it is hydrophobic and is a surfactant. Water is a polar molecule consisting of both oxygen atoms to be slightly positive and the hydrogen atom to be slightly negative. Due to cohesion, the water molecules “stick” together. Stains are usually oils and oils are non-polar. Since “likes dissolve likes”, water and oil do not mix together, so water alone cannot wash away stains. Detergents on the other hand, are long chains of hydrocarbon molecules that allow oil and water to mix so stains can be removed while rinsing. Detergents are surfactants that lower the tension of water, and making it more adhesive. The hydrocarbon chains are polar on one end and non-polar on the other so the polar end mixes with the water and the other end mixes with the oil. The oil molecules get smaller and smaller and detergent molecules begin to surround them so the polar detergent molecules are easily washed away by water.

3. a) The benefit of a water strider’s legs to be coated with a hydrophobic substance is that the substance would repel water and therefore, allow the insect to stay above the water’s surface.
b) If the legs were covered in a hydrophilic substance, the insect would have a hard time staying above water as the substance would be attracted to the water molecule. As a result, the insect would drown.

4. Plants, photosynthesis and gravity are affected by water in three ways; cohesion, adhesion and surface tension. Cohesion plays a role in moving nutrients up the plant by going against gravity. The nutrients dissolve in the water and are then carried throughout the plant. Adhesion is also involved in the transportation of nutrients because adhesion is the attraction of one substance to another. The adhesion in water molecules attract to the cell walls of plants and help in moving the nutrient filled water against the effects of gravity. In the case of photosynthesis, adhesion and cohesion are contributors because they move water throughout the plant. In order for a plant to preform photosynthesis it needs carbon dioxide, light energy and water to produce oxygen gas and glucose. If adhesion and cohesion inside the water molecules was not there then it would not be able to make the water get to the cells that need it.
Procedure & Observations
Procedure & Observations
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