Projectos De Ciencias

Abstract

This is a straightforward, fun project to measure the rate of the chemical reaction that occurs when Alka-Seltzer® tablets are plopped into water. You'll track the volume of carbon dioxide gas produced at regular intervals after the reaction begins. How does changing the temperature of the water affect the production of gas?

Objective

The goal of this project is to measure the effect of temperature on the rate of a chemical reaction.

Introduction

You may have seen a television commercial for Alka-Seltzer tablets, or heard one of their advertising slogans: "Plop, plop, fizz, fizz, oh what a relief it is!®" When you drop the tablets in water, they make a lot of bubbles, like an extra-fizzy soda. And like a soda, the bubbles are carbon dioxide gas (CO2). However, with Alka-Seltzer®, the CO2 is produced by a chemical reaction that occurs when the tablets dissolve in water.

The main ingredients of Alka-Seltzer tablets are aspirin, citric acid, and sodium bicarbonate (NaHCO3). When sodium bicarbonate dissolves in water, it dissociates (splits apart) into sodium (Na+) and bicarbonate (HCO3−) ions. The bicarbonate reacts with hydrogen ions (H+) from the citric acid to form carbon dioxide and water. The reaction is described by the following chemical equation:

acid hydrolysis of bicarbonate

The compounds on the left-hand side of the equation (bicarbonate ions and hydrogen ions) are called the reactants, and the compounds on the right-hand side of the reaction (water and carbon dioxide) are called the products.

So how does temperature come into this? In order for the reaction shown above to occur, the bicarbonate ions have to come into contact with the hydrogen ions. Molecules in a solution are in constant motion, and are constantly colliding with one another. The hydrogen and bicarbonate ions must collide at the right angle and with enough energy for the reaction to occur. The temperature of a solution is a measure of the average motion (kinetic energy) of the molecules in the solution. The higher the temperature, the faster the molecules are moving.

What effect do you think temperature will have on the speed of the bicarbonate reaction? In this project you can find out for yourself. You'll build a simple apparatus to collect the carbon dioxide gas produced by the chemical reaction. Then you'll plop Alka-Seltzer® tablets into water at different temperatures, and measure the volume of carbon dioxide gas collected at different time points.

Terms, Concepts, and Questions to Start Background Research

To do this project, you should do research that enables you to understand the following terms and concepts:

Molecules

Temperature

Reactants

Products

Reaction rate

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