Name ___________________________ Class ___________________ Date _____________
Recognizing a Synthesis Reaction
Background Information
In a synthesis reaction, two or more substances combine to form a single substance. The
substances that combine can be elements, compounds, or both. The general equation for a
synthesis reaction is A + B AB
The symbols A and B represent two elements or compounds that combine to form the
compound AB. For example, when a metal combines with oxygen from the air, a synthesis
reaction occurs. A compound called a metal oxide is produced. The reaction can be described
by the following word equation: Metal + Oxygen Metal oxide
In this investigation, you will heat copper metal in air. Then, you will examine the product to
determine whether a synthesis reaction has occurred.
Problem
How can you know when a synthesis reaction has occurred?
Pre-Lab Discussion
Read the entire investigation. Then, work with a partner to answer the following questions.
1. Calculating If the balance indicated that the test tube and 50mL beaker has a mass of
44.8 g and you want to have exactly 5.0 g of copper, what should the balance read
with the copper in the evaporating dish?
2. Predicting What evidence of a chemical change might you observe in this
investigation?
3. Predicting What observation would be evidence of a synthesis reaction? Explain
your answer.
Materials (per group)
ring stand
test tube clamp
test tube
copper powder
triple-beam balance
50mL beaker
Bunsen burner
Safety
Put on safety goggles and a lab apron. Use extreme care when working with heated
equipment or materials to avoid burns.
Procedure
1. Set up the ring stand and test tube clamp.
2. Place the Bunsen burner on the base of the ring stand. Place the test tube in the test tube
clamp. Do not light the burner yet. Adjust the position of the test tube so that its center is
directly over the burner.
3. Place the test tube in the 50mL beaker and weigh those two items together on the balance
and find its exact mass. Record this mass in the data table.
4. To measure 5.0 g of copper powder, add 5.0 g to the mass of the test tube and 50ml beaker
weight and move the riders on the balance to this number.
5. Using the scoop, slowly add copper powder to the test tube until the pointer of the balance
is centered. In the data table, record the mass of the test tube, the 50mL beaker, and the
copper powder together.
6. Place the test tube containing the copper powder in the test tube clamp.
7. Light the Bunsen burner and adjust the test tube so that it is 5 cm above the height of the
tip of the flame. Heat the test tube for 7 to 10 minutes until you observe a change in the color
of the copper powder and it turns to a liquid.
8. Turn off the Bunsen burner and allow the test tube to cool for 4-5 minutes. Use the hot
hands to place the test tube in the 50mL beaker and on the balance to find its mass. Record
the mass of the test tube, the 50mL beaker, and the product after heating.
9. Once cooled, remove the product of the reaction from the test tube. Observe its color or
colors. Record your observations in the data table.
Observations
DATA TABLE
Measurement
Mass of test tube and 50mL beaker
Mass (g)
Mass of test tube, 50mL beaker, and copper
powder
Mass of copper powder
Mass of test tube, 50mL beaker, and product
after heating
Mass of product
Observations of Product
_____________________________________________________________________________.
Analysis and Conclusions
1. Observing What did you observe as a result of heating the copper powder that might
indicate that a chemical reaction took place?
2. Inferring Explain why there was a change in mass as a result of heating the copper
powder in the test tube.
3. Classifying What type of chemical reaction occurred?
4. Inferring Was this reaction endothermic or exothermic? Explain your answer.
5. Calculating Calculate the percent change in mass by using the following formula.
Percent change in mass = Change in mass X100%
Mass of copper
6. Drawing Conclusions There are actually two different oxides of copper produced as
a result of this reaction. They are copper(I) oxide and copper(II) oxide. If all the
copper changed to copper(I)oxide, the mass would change by 12 percent. If all the
copper changed to copper(II) oxide, the mass would change by 25 percent. Based on
the percent change in mass, what must have been produced as a result of the reaction?
7. Calculating Write a balanced chemical equation for the synthesis reactions that took
place.
8. Evaluating Compare the percent change in mass that you calculated with those
calculated by your classmates. What variables could account for differences between
your results and those of your classmates?
9. Controlling Variables How could these variables be controlled so that the results
obtained are more precise?
10. Observing Copper(II) oxide is black and copper(I) oxide is red. Do your
observations support your answer to Question 7? Explain your answer.
Go Further
Caulking compound is used to make a watertight seal around bathtubs, sinks, and pipes. A
synthesis reaction occurs when caulking compound is placed on a surface and exposed to the
air. This reaction leads to hardening of the soft caulking compound. To investigate the role of
water in this reaction, place a small amount of caulking compound on two small pieces of
wood or cardboard. Place one of the pieces in a beaker and cover it with water. Leave the
other piece exposed to the air. After 5 minutes, use a glass-stirring rod to probe each sample
of caulking compound and compare the firmness of the two samples. Record your
observations. Repeat this observation every 5 minutes for 30 minutes or until one of the
samples becomes firm and rubbery. Report your conclusions about the role of water in this
synthesis reaction.