Lab The Scientific Methoddrop Lab Worksheet

Lab: The scientific method/drop lab worksheet Instructions: Type your answers directly on this document and print out when completed. Names: 1. Making observations List five general properties of liquids (0.25 pt): a. Boiling/ Freezing Point b. Surface Tension c. Color d. Temperature e. Volume 2. Asking a scientific question From your list of properties and using only the equipment at your lab bench, choose one that you will be able to measure in lab today. It is important that you choose a measurable property which will allow you to distinguish the four solutions from one another. Property to be tested (0.25 pt): Surface Tension 3. Stating the hypothesis Briefly state the hypothesis that you are testing. Remember that a hypothesis has to be specific, testable and refutable. Based on your background knowledge, create a hypothesis which will predict the outcome of your experiment. Include in your hypothesis a description of how intermolecular bonds explains the relationship between the independent and dependent variables. It is a good practice to state a hypothesis in the form of “If [condition], then [prediction].” For example, “If a cell is placed in a hypotonic solution [condition or cause], then the solution will become transparent (clear) [prediction or effect]. Note: make the hypothesis universal, then observe how the hypothesis applies to your specific lab. Finally, be sure NOT to reverse cause and effect (e.g. “If the solution clears, then the cells burst”). (0.5 pt): Hypothesis: If the solution has strong intermolecular forces, then the diameter will be relatively small. 4. Describing experimental procedures Describe below your exact procedure for measuring that property. Your description should in paragraph form, in the past-tense and be detailed enough so that another experimenter can exactly reproduce your procedure. (1 pt) A pipette was used to take five microliters of each of the four liquids and transfer them onto a blank slide. The diameter of each drop was measured in centimeters using a ruler. The measurements were recorded into a data table. This process was repeated three times. 5. Choosing and controlling experimental variables a. State your independent variable (0.25 pt): Type of liquid b. State your dependent variable (0.25 pt): Diameter (cm) c. List at least four controlled variables (0.5 pt): Room temperature, amount pipetted (five microliters), blank glass slides, member who pipetted the liquid. 6. Presenting scientific data Use the “Using Excel to Present Data” document to guide you through this portion. a. Record your data in an Excel table. Paste this table below as your experimental results. Label this table as Table 1 and give this table a descriptive title based on its content. (1 pt) Table 1. The diameter in centimeters of four different liquids. Liquid Type Diameter (cm) Trial 1 Trial 2 Average (cm) Trial 3 Standard Deviation Water 0.6 0.4 0.4 0.47 0.12 Ethanol 1.5 1.5 1.5 1.5 0 Potassium Chloride 0.5 0.3 0.35 0.38 0.10 Isopropanol 0.6 0.7 0.5 0.6 0.1 b. Graph your results in a way which best summarize the message that you want to convey from this experiment. Scientific experiments are set up to generate explanations about the observations that are made. Make sure that your graph conveys that explanation. Include all components of proper graphing technique (axis labels, proper units, title, etc.). (2 pt) Figure 1. The average diameter of four different liquids. 7. Interpreting scientific findings Clearly and concisely explain the results of your experiment, including the identity of each of the four solutions. Use your lab handout as a guide to explain your experimental results. Do not restate your results, instead explain the reason (the science!) behind them. (4 pt) A smaller drop diameter indicates the solution has stronger intermolecular forces. There are two main intermolecular forces, dipole-dipole and ion-dipole, which are present in polar molecules. In a polar molecule, the atoms of the covalent bond are not evenly distributed. Dipole-dipole forces are the attraction of the negative end of one molecule to the positive end of another molecule. Three of the four molecules presented dipole-dipole forces. These three solutions consisted of water, isopropanol, and ethanol. Water had the second smallest diameter which means that out of the three it had the strongest dipole-dipole force. This is because water is the most polar solution. The oxygen atom present in water contains eight protons and each hydrogen atom bonded to the oxygen atom has one proton. Even though the polar bonds are relatively weaker, water has a very strong surface tension. Ethanol had the third smallest diameter and isopropanol had the largest diameter. Ethanol is less polar than water but more polar than isopropanol. This is because the oxygen atom is bonded to a carbon atom in Ethanol whereas the isopropanol oxygen atom is bonded to two additional carbon atoms. Ion-dipole forces were present in only one of the solutions which was Potassium Chloride (KCl). KCl had the smallest diameter which showed that it contained the strongest intermolecular forces out of the four solutions. The ion-dipole forces allow the positively charged potassium and the negatively charged chlorine to completely disband which allows them to bond to other molecules in their environment. Overall, after viewing the measurements, ion-dipole forces are significantly stronger than dipole-dipole forces.