Observing a Candle Lab

Observing a Candle:

Background:

                You will observe a burning candle in this experiment.  When you light a candle, you initiate a chemical reaction called combustion. This reaction is expressed as follows:

                hydrocarbons + oxygen à carbon dioxide + water + heat/light

                C_nH_2n+2 + O₂ à CO₂ + H₂O + energy

                Combustion reactions require three things to take place: fuel (hydrocarbons), oxygen, and ignition. Hydrocarbons are molecules made up of hydrogen and carbon and substances such as gasoline, fuel, oil, and propane are examples of hydrocarbons.

                In this experiment you will use a candle, which is also a hydrocarbon. You will use oxygen in the atmosphere, and you will supply ignition with a match.

                It may seem odd to think that burning the candle produces water. It is hard to see the water that results from burning the candle because it is a gas. Carbon dioxide is also a gas and it is more dense than air, so it “sinks” and can be separated from air easily.

                When CO₂ is added to a calcium hydroxide, Ca(OH)₂, solution (limewater), it reacts to form insoluble calcium carbonate, CaCO₃. This substance is white and when the reaction occurs, it makes the solution turn cloudy because of the insoluble CaCO₃. 

Pre-Lab Questions:

1.  What happens to a candle when you light it? What is your evidence that it is a chemical reaction?

2.  How can you prove that a candle needs oxygen to burn?

3.  How can you prove that a candle produces carbon dioxide when it burns?

4.  How can you prove that a candle produces water when it burns?

5.  Is it possible to light a candle without directly touching the flame and the wick? Why or why not?

Purpose:

You will make a series of observations to hone your observation skills for future experiments. You will learn something new about an object you assume is familiar.

Materials:

Candle                                                  Petri Dish

Matches                                              400mL beaker

Ruler                                                     CO₂ indicator solution in a beaker

Balance

Procedure:

Once you have made observations, if you feel you don’t quite understand what you’ve observed, check in with your teacher to discuss before moving on to the next part.

PART I: Observations of the Candle

1. Record some quantitative observations about the candle before you light it. Record things such as length, mass, diameter, length of wick, or anything else that occurs to you. Try getting the mass of the candle at specific time intervals while burning: does its mass change over time?
2. Record some qualitative observations about the candle before you light it. Record such things as wax color, color of wick, smell, new/old/damaged, or anything else that occurs to you.
3. Record the sequence of events that occurs as you light the candle. Try to be as detailed as possible. These observations will be qualitative and should be as organized as possible.

PART II: Candles Use Oxygen as They Burn

1. When the chemical change called combustion happens, oxygen must be present. Oxygen is a gas that makes up about 20% of Earth’s atmosphere (by volume). Can you prove that oxygen from the air is required for the candle to burn? As a group, suggest a procedure and try it out.
2. Write down what you observe in your experiment, whether it seems relevant or not.

PART III: Candles Produce Carbon Dioxide as They Burn

1. Combustion produces carbon dioxide (CO₂). Recall from the background a way to detect CO₂ using a solution. Devise and carry out an experiment to test whether a candle releases CO₂.
2. Write down what you observe in your experiment.

PART IV: Candles Produce Water as They Burn

1. Combustion reactions also produce water (H₂O). Because the candle also releases heat, if water is present you will have to provide a way to cool it down to see it. Can you prove that candles do release H₂O? Devise and carry out an experiment.
2. Write down what you observe in your experiment, whether it seems relevant or not.

PART V: Flames Have Parts

1. There are at least three distinct regions in a candle flame. One: the blue-rimmed clear region very close to the wick. Two: the dim-orange-fading-to-bright-yellow region that produces light. Three: the clear region just above the visible flame. Observe these flame regions.

PART VI: Flames Can Be Surprising

Your teacher will show you the “jumping flame trick.”

1.  Describe how to perform the jumping flame trick in your own words.

2.  What makes the trick possible?

3.  What burns in a candle: the wick, the solid wax, the melted wax, or vaporized wax? Justify your answer.

HW #3 for 1/21

1) HW #3: pg. 184 #4-5, pg. 211 #16

HW #2 for 1/19

1) HW #2: pg. 210 #8-9, 13, 14 (except e & f), 15
2) Take Home Lab #1 due Tues 1/19

HW #1 for 1/14

 1) HW #1 pg. 176 exer 6.1, pg. 177 exer 6.2 (yellow boxes), pg. 210 #3-6
2) Take Home Lab #1 due Tues. 1/19

Take Home Lab #1 spring semester

Take Home Lab #1:  Growing Crystals

Question: How are crystals of different crystals similar and different?

Safety: Do not eat any of the crystals or other materials during this activity, as mold quickly grows on some of the crystals. Mark the cups clearly and keep them out of the reach of children .Clean up spills immediately.

Materials: cups, water, sugar, salt, Epsom salt, thread

Procedure: In this lab, you will grow three different types of crystals: sugar, salt and Epsom salts. Crystals are grown by either dissolving more material than the solvent (the water) can normally hold by heating it, or by allowing the solvent to evaporate over time. In this procedure, you will do a little of both. You will put a lot of solute (the substance that dissolves) in a little solvent and heat it to dissolve; then you will let it sit for a few days to evaporate.

1. For each of the solutes (salt, sugar, Epsom salts), dissolve a large spoonful in 1 cup of boiling water in a glass cup.  (Be careful when boiling water please!) For sugar you will need to add 2-3 large spoonfuls of sugar to 1 cup of boiling water. Stir until all of the solute is gone.

2. Tie a paperclip to the end of a short thread and tie to a pencil or pen to hang in the water with the dissolved solute.  Allow it to sit on a windowsill for several days while the water evaporates. Pull the string out and let the crystals dry overnight.  Record observations of your crystals every day and include the number of crystals, size, shape and other characteristics.

3. Find a good example of each crystal and sketch its shape. Try to find a single crystal without other crystals growing out of it.

Post-Lab Questions:

1. Make a daily log for 5 days of your crystals.  Make a sketch for each(sugar, salt, Epsom salts) one during these 5 days.  Note the number and shape in your drawings. Make it as accurate looking as possible.

2. Which substance grew the largest crystals?

3. How would you describe the shape of each crystal? Describe all three and they will have different shapes!

4. You used three different chemicals to grow these crystals: salt (NaCl), sugar (C₁₂H₂₂O₁₁) and Epsom salts (MgSO₄).  Which of these molecules is the largest (hint: look at their chemical formula)? Did that substance grow the largest crystals? Did the chemical with the smallest molecule grow the smallest crystals? Explain.

Chapter 17 Test Study Guide

Study Guide for Chapter 17 Tet for 12/11

--Understand that reactions occur because of collisions between molecules
--Know how reaction rates are affected by surface area, temperature and concentration
--Know how a catalyst affects a reaction and its activation energy
--Know the difference between a heterogeneous and a homogeneous reaction
--Know how to write the equilibrium expression (K) for homogeneous and heterogeneous reactions
--Understand why solids and liquids in an equilibrium expression have a value of 1
--Know how to calculate and equilibrium expression when numerical values are given
--Know how conditions affect the equilibrium of a reaction such as adding or removing reactants and products, adding or removing energy
--Know the difference between an exothermic and endothermic reaction
--Know how volume affects the gas in equilibrium, if volume decreases the amount of molecules has to decrease and if volume increases, the molecules would increase

HW #10 for 12/10

1) HW #10 pg. 625 #2, 3, pg. 629-630 #29, 31-32
2) All late HW due Friday
3) Composition books due this week
4) Chapter 17 test Friday