- Put bottled water two Styrofoam cups. Take one of the cups and add table salt in it. Mix it until the salt will not dissolve any longer. Put both cups in the fridge. Set the fridge to 1 degree Celsius. Leave them there overnight.
- The next day, take out the salt water and mix it again to make sure it is saturated. Put the Styrofoam cup containing the salt water into a second Styrofoam cup.
- Take an eye dropper, fill the eye dropper with salt water
- Take the graduated cylinder and position it so that the end of the eyedropper is 2cm from the bottom of the graduated cylinder. Record the start volume of the liquid inside the cylinder (0 cm in this case).
- Slowly drop 10 drops into the cylinder, maintaining a 1 cm distance between the liquid and the end of the eyedropper. Record the volume. Dispose of the remaining water inside the dropper. Fill the dropper again with salt water. Drop 10 drops into the cylinder. Make sure to carefully count every drop! Record the end volumes.
- Repeat step 5 five times.
- Clean out the graduated cylinder using tap water, and use paper towels to dry it clean.
- Put the salt water back into the fridge.
- Take out the cold water (from the fridge), put it in another Styrofoam cup and repeat what you did in step 5-8.
- Put the water in the microwave and heat it at high power for 1 minute.
- Take it out, stir the water, measure the temperature (and write it down) and use the water to do steps 5-8 again.
- Take the salt water out, microwave it at high power for 1 minute.
- Repeat what you did in step 12 for the salt water.
- Clean everything up.
Data Collection
Attached to the back of the lab.
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Data Processing and Presentation
Difference = End volume – start volume
Ex. End volume = 2.11ml, start volume = 2.00ml 2.11ml – 2.00ml = 0.11 ml = difference
Volume per drop = Difference / 10 Ex. Difference = 0.11ml
0.11ml/10 = 0.011ml = Volume per drop
Cold bottled water at 0.5+ 0.02 degrees Celsius
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Rounded: 0.015ml
Uncertainty: + 0.02 / 10 = + 0.002ml
Volume per drop = 0.013ml to 0.017ml
Warm saturated salt water at 38 + 0.5 degrees Celsius
Average volume per drop: (0.010+0.021+0.013+0.015+0.011) / 5 = 0.014ml Uncertainty: + 0.02 / 10 = + 0.002ml
Volume per drop = 0.012ml to 0.016ml
Conclusion and Evaluation
Our experiment tested two variables (the type of liquid and the temperature) and how they affected the volume of a drop. From our experiment, there is a slight difference between the volume of bottled water and the volume of salt water, so therefore it proves that the volume of a drop is dependant on the type of liquid we use.
I also hypothesized that salt water would contain a smaller volume per drop than bottled water. This hypothesis was disproved in the experiment. We found that the volume of a drop of bottled water at 0.5 degrees Celsius is 0.01ml less than the volume of a drop of saturated salt water at 0.5 degrees Celsius.
For our experiment, we couldn’t prove that temperature affected the temperature affects the volume of a liquid because the volume of a drop of our bottled water increased by 0.02ml while the volume of a drop of warm saturated salt water remained exactly the same. Quite unexpectantly, we discovered that a drop of bottled water is greater in volume than a drop of salt water after they’re heated up to 38 degrees Celsius.
All our data, however is only true IF we disregard the series of lab errors that may have altered the results. Here is the list of lab errors:
Lab Errors:
- Every drop that comes out of the eyedropper is a result of gravity pulling the drop of water out of the eyedropper opening. Because the force of gravity is constant, we can assume that every drop has the same volume, unless there was another force involved. This other force is the shaking of the hand holding the eyedropper. To prevent this, we first planned to tape the eyedropper to a ring stand. This way it would stay motionless so that no other force except gravity would act on every individual drop. Unfortunately, the eyedropper was not long enough to reach far enough into the graduated cylinder, therefore we held the eye dropped ourselves while dropping the liquids. For this reason, the shaking of our hand may have affected the results of our data.
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- To prevent liquids from splashing onto the sides of the graduated cylinder, we decided to make every drop 1 cm above the liquid inside the cylinder. This would prevent each drop from making the water splash too much.
- Since we couldn’t use the ring stand, the drops may have gotten stuck to the sides of the graduated cylinder because we couldn’t guarantee that the eyedropper was held vertically over the water. Even if we did make sure it was vertically straight, our hands might have shook, flinging the drop so that it would hit the side.
- Water evaporation may have occurred when we were performing the lab, so before recording the data for 10 drops, there may have been a little bit of water that had evaporated so each drop is actually slightly bigger than what we had recorded.
- We are not 100 percent sure that we counted the correct number of drops because there seems to be a few trials that had an unusually large volume compared to the other trials. This may have also been because the water stuck to the sides of the graduated cylinder came down and added to the volume of one trial.
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Since the graduated cylinder we used only went up in 0.5ml increments, we had to estimate the 0.01ml values. Our data may be off by 0.01 or 0.02ml (thus a + 0.02ml error).
- Atmospheric pressure affects the results slightly. This is something we cannot control, however we did the entire in a short period of time, so the atmospheric pressure should have been somewhat the same during that period of time.
- We couldn’t make sure that NO heat would be lost or gained when we took the cold
water from out of the fridge or when we took it out of the microwave. We insulated the water with 2 Styrofoam cups, but even that couldn’t make sure that no heat would be gained or lost. Also, water would lose or gain heat as we are dropping each drop, or when it is sitting in the graduated cylinder, waiting to be measured and recorded. For this reason, each drop may be a little bigger or smaller in volume than our recorded values.
- We tried to control the saltiness of the salt water by making it saturated salt water. To do this, we put much more salt than is needed to saturate the water, into the container. We stirred until no more salt was dissolved, or so it seemed. We couldn’t be absolutely sure that the water was saturated because maybe the salt was just dissolving more slowly, but it was still being dissolved.
- When we were heating up the water inside salt water, we still had a little bit of salt left on the bottom.. This may have caused a problem because when we wanted saturated water, we wanted it saturated at 0.5 degrees. After we heat the salt water, it wouldn’t be saturated anymore, so more salt would be able to be dissolved into the solution. This means that the salt water after getting heated was slightly saltier than before it was heated.
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