Question

Temperature and Phase Changes In this exercise, you will make observations of the phase changes of water (H 2 O). You will measure temperature and create a heating curve to determine the melting point and boiling point of water. 1. Gather the 250-mL beaker, approximately 150 mL of crushed ice, a watch or timer, the thermometer, burner stand, burner fuel, and matches. Note: Large ice cubes may be crushed by placing them in a large plastic bag, placing the bag on a durable surface, and breaking the pieces apart with a hammer or other heavy object. 2. Fill the beaker to about the 150-mL line with crushed ice. 3. Place the thermometer in the center of the ice. Do not allow the thermometer to touch the sides or bottom of the beaker. 4. After holding the thermometer in the ice for about a minute, note the time and record temperature at 0 minutes in Data Table 2 of your Lab Report Assistant . Additionally, record your observations about the state of matter (solid, liquid, or gas) of the water in Data Table 2 . 5. Uncap the burner fuel, light the wick with a match or lighter, and place the fuel under the stand on a pie pan. Burner setup. Note that the flame is blue which is sometimes difficult to see. 6. Place the beaker on the burner stand. Keep holding the thermometer in the middle of the ice. 7. Start the timer and begin taking temperature and observation readings every minute, recording your findings in Data Table 2 . Note: It is important that you record both the temperature AND the state or states of matter present every minute throughout the experiment. 8. Gently stir the ice with the thermometer as it heats. www.HOLscience.com 13 ©Hands-On Labs, Inc. Experiment Liquids and Solids 9. Continue to stir the ice or water and record temperature and observations every minute until the water has boiled for 5 minutes . Do not allow the thermometer to rest on the glass of the beaker. 10. Extinguish the burner fuel by lightly placing its cap over the flame; do not tighten cap until the burner fuel container has fully cooled. 11. Thoroughly wash and rinse the equipment for future use. Questions: A. Using the temperature data recorded in Data Table 2 , create a heating curve. ● Plot time (minutes) on the x-axis (horizontal axis) and temperature (°C) on the y-axis (vertical axis). Connect the plotted points with a line. ● Label the heating curve to show each phase of matter (solid, solid + liquid, liquid, liquid + gas). ● Label the melting point and boiling point on the heating curve. Note: An example heating curve is given in Figure 6 of the Background B. Are there parts of the curve with positive slopes and parts that are flat (slope of zero)? What states of matter are present when the slope of the heating curve is positive and what states of matter are present when the slope is zero or close to zero? C. Describe the key characteristics for the three states of matter. D. Define the melting point. What was the observed melting point of water?

E. Define boiling point. What was the observed boiling point of water?

F. What happens to heat energy when it is not increasing the temperature of the substance in the beaker? Use your heating curve to explain your answer. G. Was temperature perfectly constant during your test while the water was melting and while it was boiling? Explain why or why not.

H. The published melting point of H 2 O is 0°C, and the published boiling point is 100°C. Why may you have found different values?

I. Use the following information to determine if the intermolecular forces of isopropyl alcohol are greater or weaker than the intermolecular forces of water. Explain your answer. The melting point of isopropyl alcohol (rubbing alcohol, C 3 H 8 O) is about -90 °C and the boiling point is about 82 °C

Answer 1

Answer D)

Melting point is that temperature at which solid and liquid states of a substance exist in equilibrium. Below this temperature, solid predominates.

Water has melting point 273.15 K at 1 atm pressure.

Answer E)

Boiling point is that temperature at which liquid and gaseous forms coexist in equilibrium. At this temperature, vapor pressure equals the atmospheric pressure.

Boiling point of water is 373.15 K at 1 atm.

Answer F)

Heat energy is used up for phase change. It provides latent heat of fusion during melting and latent heat if vaporization during boiling

Answer G)

Yes, the temperature will be constant as whole of the heat is used up in phase change till whole of the substance is in single phase.

Answer H)

Different values may be due to presence of non volatile solutes which elevates the boiling point but decreases melting point.

Answer I) Boiling point of isopropanol is less than water. So, its intermolecular forces are less than water