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Sample Lab Report Dr. Gina Little CHEM 123-XX Aug. 18, 2011 Measuring the Density of Ice and Liquid Water Purpose This lab experimentally measures the density of a water sample in its ice phase as well as its liquid phase. The experimental density values are compared to known density values obtained from a reference book. Procedure Place approximately 5 ml of warm distilled, deionized water into a clean, dry 10.0 ml graduated cylinder that has been preweighed. Freeze the filled graduated cylinder in an ice bath. Record the volume of the ice and the mass of the ice and graduated cylinder. Melt the ice in the graduated cylinder and record the volume of the liquid water as well as the mass of the water and graduated cylinder. Repeat procedure for a second trial. Data Trial I Trial II Volume of ice 6.22 ml 6.94 ml Mass of ice + cylinder 24.1 g 24.7 g Mass of cylinder alone 18.5 g 18.4 g Mass of ice* 5.6 g 6.3 g Volume of liq. water 5.62 ml 6.53 ml Mass of liq. water + cylinder 24.1 g 24.8 g Mass of cylinder alone 18.5 g 18.4 g Mass of liq. water * 5.6 g 6.4 g Calculations *mass ice = 24.1 – 18.5 = 5.6 g mass of liq. water = 24.1 – 18.5 = 5.6 g D= M/V Dice = 5.6 g/6.22 ml = .900 .90 g/ml Dwater = 5.6 g/5.62 ml = .996 1.00 g/ml %Error = 100% * |(Actual value – Measured value)| / actual value % Error = 100% * |.931 - .91| / .931 = 2.25 2.3% Trial I Trial II Avg. Literature 1 error Density of ice .90 g/ml .91 g/ml .91 g/ml .931g/cm 3 2.3% Density water 1.0 g/ml .98 g/ml .99 g/ml 1.00g/cm 3 1.0% NOTES FOR GOOD LAB REPORT GRADES Intro: Remember to use your own words*, but look at the manual’s intro for ideas. Procedure: BRIEFLY describe the steps (in paragraphs, preferably). Do NOT include details about standard lab procedures (heating, weighing). Do NOT discuss calculations; that comes later. Use the same tense and voice throughout (this is 3rd person present tense). Data and Calculations: You will NOT include a Data or Calculations section. The datasheet, which you should include as a second file, will replace the Data and Calculations. I included it here to show you how lab reports normally look and so that the conclusions make sense to you. 1 http://www.edinformatics.com/math_science/ice_java.htm Sample Lab Report Conclusion The calculated densities obtained from this lab were very close to the values reported in the literature. Curiously, although they were only 2.3% off , both trials of the ice density generated lower than expected densities. Small air bubbles trapped in the ice samples would make the volume of ice readings higher than they should be (and thus the density would appear lower than expected), and might account for some of the error. The error could also have been caused by water impurities with something else that was less dense. It was noticed that the measured masses of each sample remained identical from solid to liquid phase. The only way the mass could have changed from melting is if ice or water was lost between weighings. This shouldn’t happen as mass cannot be created nor destroyed. The second mass measurement was thus unnecessary. It was also observed that density appears to be an intensive property. An intensive property is one which does not depend on the amount of matter being studied. The mass of water varied between trials, yet the calculated densities were the same. Our results were very accurate with only 2.1% and 1.0% errors. The density of a substance can vary with its phase and its temperature. To reduce errors, when measuring the liquid water volume, it is important to ensure that the water temperature is as close to zero as possible, but that all of the ice has melted. Ice was found to have a lighter density than water. This property explains why ice floats in water, or solutions that are mostly made of water. If you put ice cubes in a liquid like ethanol (d= 0.8 g/mL), which is less than the 0.91 g/mL density of ice, one would expect to see the ice cubes sink instead of floating. Datasheet Questions 1) Why isn’t tap water used for this experiment? Distilled, deionized water is used instead of tap water because it is more pure. The impurities in tap water (like minerals) have different densities than water and would have created error. 2) If the ice is allowed to thaw until it reaches room temperature, how would that affect the measured density? The density of a substance is temperature dependent. If the ice is allowed to thaw until it reaches room temperature, we would be measuring the density of water at 20 C, which is less dense than 4 C water. 3) An empty graduated cylinder weighs 25.55 g. When filled to 55.0 ml with an unknown liquid it weighs 227.21 grams. What is the density of the liquid. Dliq = mliq / Vliq = (227.21 g – 25.55 g)/55.0 ml = 201.66 g/ 55.0 ml = 3.666 3.67 g/ml *A note about academic dishonesty (“plagiarism”): To use someone else’s words is plagiarism. It doesn’t matter if it is taken from the manual, the internet or even your lab partner. To avoid the consequences, paraphrase or cite the original writing. Conclusion: Remember to use your own words*, but you can look at the manual or talk to your lab partner for ideas. Briefly discuss your results, and then explain how close they were to expected. Discuss any errors and how they would change your calculations and results. For full points, I am looking for insight into what the lesson of the lab was. Read the intro and try to show that you accomplished the goal. Summarize your lab in one or two sentences. Mention any real-life significance of the lab. State any things you have learned in the lab (briefly!). Note that the voice (3rd person) is consistent throughout. 1st or 2nd person are also okay, although 3rd is commonly used in science. Lab Questions The lab questions are part of the datasheet, so they will not appear in the report portion. But, since the lab questions are designed to help you notice things you’re supposed to be learning in lab, you’ll probably want to comment on them in your conclusions also.