Endothermic Reaction (Anna Mkrtchyan)

In this investigation, students will work in groups of 3 to explore what is a chemical reaction and what happens to the reaction rate when you change parameters in the reaction. The materials used in this lesson allow students to safely conduct their investigations, as well as allow for safe and convenient disposal of materials. All materials are available in supermarkets or educational suppliers.

Research Question and Hypothesis

Some chemical reactions absorb energy and are called endothermic reactions. What happens to the reaction rate when you change parameters (ratio of reactants) in the reaction.

Standards

High School Chemistry: Chemical Thermodynamics

7. Energy is exchanged or transformed in all chemical reactions and physical

changes of matter. As a basis for understanding this concept:

a. Students know how to describe temperature and heat flow in terms of the

motion of molecules (or atoms).

b. Students know chemical processes can either release (exothermic) or

absorb (endothermic) thermal energy.

9-12.II.B.1 - Chemical Reactions

Independent variable

The independent variable is time. It will be measured in seconds.

Dependent variables

The dependent variable is Temperature. It will be measured in 0C.

Series

Study the temperature of reaction (dependent variable) as a function of time (independent variable) at various parameters (ratio of reactants) in the reaction (series).

Constants and Controls

Constant-the amount of cabbage juice, the type of chemicals, the way chemicals are mixed in the bag

Control-1:1 Ratio of sodium hydrogen carbonate and citric acid

Materials

Endothermic reaction

citric acid (C₆H₈O₇)

sodium hydrogen carbonate (NaHCO₃)

purple cabbage juice

Citric acid is a white crystalline powder and is used as a flavoring and preservative in food and beverages, especially soft drinks. Citric acid can be added to ice cream as an emulsifying agent to keep fats from separating, to caramel to prevent crystallization, or to recipes to replace fresh lemon juice. In the home, it can be used to soften water, which makes it useful in soaps and laundry detergents. It is an active ingredient in some bathroom and kitchen cleaning solutions to remove hard water stains from glass without scrubbing.

Sodium hydrogen carbonate (sodium bicarbonate) has long been known and widely used. It is referred to as baking soda and used in cooking as a leavening agent. Many laboratories keep a bottle within easy reach since it is amphoteric, so it can react with acids or bases. Mixed with water, sodium bicarbonate can be used as an antacid to treat acid indigestion and heartburn. It has also been known to be used in treating scalding, preventing blistering and scarring. Toothpastes containing sodium bicarbonate has shown to have better whitening properties and plaque removal than toothpastes without it. Baking soda is also effective as a odor remover, clothes softener and used in fire extinguishers.

• How to make a cabbage juice: Shred a handful of red cabbage and boil for 5 minutes. Let it cool, and store.

Procedures

Sample data and graphs

Analysis & Conclusions

Ask students to complete a summary in their notebooks of what type of reaction they believe this investigation was, endothermic or exothermic. Students should use evidence from the investigations to justify their answers. Students should point out based on the theoretical background that the difference between final and initial temperature is enough to determine the type of reaction. Endothermic reactions absorb heat energy from the environment. Reaction rates can be increased if the concentration of reactants is raised. An increase in concentration produces more collisions. The chances of an effective collision goes up with the increase in concentration. Only experimental observation reveals the link between concentration and reaction rates.

Photos

References

Chemical Investigations

Effects of temperature, concentration, catalysts, inhibitors on reaction rates

Science Learning Adventures