Heating and cooling curves lab answer key

States of Matter

Chelsey Grasham

Lab Report Assistant

Purpose: The purpose of this experiment was to determine melting and boiling points of certain substances.

Procedure: For this experiment, I collected different substances, heated them, boiled them, and observed them while recording data.

Conclusion: From this experiment, I learned that different substances have different boiling points and that the boiling/melting point of a substance can tell you about its identity.

Exercise 1: Determination of a Melting Point

Data Table 1. Melting Point of Tetradecanol.

Melting Point of Tetradecanol (°C)

Trial 1

38

Trial 2

39

Trial 3

40

Average of the 3 Trials

39

Questions

A. Describe your results for the melting point of tetradecanol. Were your results consistent? What was the range of values? My results remained fairly consistent and my values only ranged from 38-40 degrees Celsius.

B. Describe what occurs to the particles of a substance when the substance melts. Explain why this occurs. As a substance melts, the bonds begin to lose their strength and in turn, the substance turns into a liquid.

C. When performing this experiment, when is the tetradecanol in a condensed phase? Explain your answer. In this experiment, tetradecanol is in a condensed phase when it is a solid/going into the liquid stage. This must be due to the fact that the molecules are really close together.

D. Based on your observations of tetradecanol when it reformed a solid after melting, does tetradecanol form a crystalline or amorphous solid? Explain the difference between these two terms as part of your answer. I do not think tetradecanol is a crystalline solid because those kinds of solids usually go back to their solid form, from liquid the liquid form, in a very long time. This is not what happened. I believe it is a amorphous solid because it went back to a solid almost immediately.

E. Give some examples of how it might be useful to know the melting or boiling points of a substance. Think in terms of both scientific and commercial/industrial settings. Melting and boiling points are very important to know. For example, in commercial industries, like when jewelry is made, it is beneficial to know the melting points of the metals so they will be able to melt, and form the metals not jewelry. In a scientific point of view, it is important to know for safety and hazardous reasons.

F. Describe any possible sources of error for this exercise. Sources in error could include reading the thermometer incorrectly, setting the experiment up incorrectly, or not allowing things to heat for the time allowed.

Exercise 2: Temperature and Phase Changes

Data Table 2. Temperature and Observations for Heating Curve.

Time (Min)

Temperature (°C)

Observations

0

0

Starting point

1

6

Starting to change form around 25 seconds

2

9

70 percent liquid

3

15

90 percent liquid

4

30

100 percent liquid

5

55

Bubbles beginning to form

6

72

7

90

bubbling

8

99

Starting to boil really quickly

9

100

Beginning to steam

10

100

Condensation and steam forming

11

100

Condensation and steam forming

12

100

Condensation and steam forming

13

100

Condensation and steam forming

14

100

Condensation and steam forming

15

100

Condensation and steam forming

16

100

Condensation and steam forming

17

100

Condensation and steam forming

18

100

Condensation and steam forming

19

100

Condensation and steam forming

20

101

Still boiling

21

102

Still boiling

22

101

Less water, a lot of steam

23

100

Less water a lot of steam

24

100

Less water a lot of steam

25

101

Condensation and steam

26

101

Condensation and steam

27

100

Condensation and steam

28

101

Liquid getting less and less, steam

29

101

Steam and condensation

30

100

Almost no liquid, steam

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.

· Save an image of the graph.

· Resize and insert the image below.

·

Melting point

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? The curve keeps a positive slope until it reaches the 8-9 minute mark, and at that point it begins to flatline. The slope is the ice as it goes from the sold to liquid form and from a liquid to a boil and then to a gas. When the slope is zero it is vaporizing.

C. Describe the key characteristics for the three states of matter. Solid: constant shape and volume, Liquid: No constant shape but constant volume, Gas: no constant shape or volume

D. Define the melting point. What was the observed melting point of water? The melting point is the temperature when the solid is completely turned into a liquid. The melting point of water is between 0-5 degrees Celsius.

E. Define boiling point. What was the observed boiling point of water? Boiling point is the temperature that is required to make a liquid start vaporizing or turning into a gas. The boiling point for water is 100 degrees Celsius

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. This happens when the temperature reaches the boiling point and only increases maybe a few degrees, or none. This happened in the last 15 minutes and the energy was used to vaporize the water into gas.

G. Was temperature perfectly constant during your test while the water was melting and while it was boiling? Explain why or why not. The temperature was not perfectly constant. The temperature of the liquid increased until boiling 100 degrees Celsius.

H. The published melting point of H2O is 0°C, and the published boiling point is 100°C. Why may you have found different values? Altitude, accidentally adding more/not enough ice, incorrect reading of the thermometer.

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, C3H8O) is about -90°C and the boiling point is about 82°C. I do think the IMF of rubbing alcohol are greater than water. I believe this because of the information provided.

Exercise 3: Observing Gas Properties - Flammability

Chemicals

Observations

HCl

Liquid, clear

Zn

Solid, gray, shiny

HCl + Zn Reaction

It bubbled at the bottom, the hydrochloric acid was still a clear liquid

Gas + Flame

When gas was added, a small fire appeared and the gas became ignited

Questions

A. In this experiment, there were two possible identities for the gas produced: hydrogen or chlorine, which have quite different properties. Hydrogen is a colorless, odorless, flammable gas. Chlorine gas is greenish yellow with a pungent, bleach-like odor and is non-flammable. Use your observations to determine which gas was produced in this experiment. Hydrogen gas was produced because there was a loud popping noise, an explosion

B. As gas moved into the pipet bulb, where did the water go? The gas forced the water out and to the test tube, and the gas replaced the water

C. Explain why the production of a gas in this experiment is or is not different from the formation of water vapor in the heating curve experiment. It is different, this is because unlike the heating curve, there was no heat applied to this experiment, and the experiment was a chemical reaction.

Heating Curve

Temperature © 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 6 9 15 30 55 72 90 99 100 100 100 100 100 100 100 100 100 100 100 101 102 101 100 100 101 101 100 101 101 100

Time (Minutes)