Alka Seltzer Dissolving In Water

Determination of the mass of carbon dioxide evolved by Alka Seltzer using an electronic analytical balance

Writer(due south): Kevin Bryan, George Lyle

Sit-in Equipment - Teacher'south Guide
SED 695B; Autumn 2005

Principles illustrated:

Conservation of mass
Diffusion of gases
Dissolving of gases in liquids

Standards addressed:

California Country Standards for Chemistry

3. The conservation of atoms in chemical reactions leads to the principle of conservation of matter and the ability to calculate the mass of products and reactants. Equally a ground for agreement this concept:
east. Students know how to calculate the masses of reactants and products in a chemical reaction from the mass of 1 of the reactants or products and the relevant atomic masses.

4. The kinetic molecular theory describes the motion of atoms and molecules and explains the properties of gases. As a basis for agreement this concept:
b Students know the random movement of molecules explains the diffusion of gases.

6. Solutions are homogenous mixtures of ii or more substances. As a basis for understanding this concept:
b. Students know how to draw the dissolving process at the molecular level past using the concept of random molecular move

Materials

Explanation of principles involved

Residual,
Water,
100mL chalice,
Thin clear plastic to cover the chalice,
Alka-Seltzer tablet

Every bit an Alka-Seltzer tablet dissolves in water, it liberates carbon dioxide. The carbon dioxide dissolves in the water and then comes out of solution as a gas.

This carbon dioxide gas has mass, just since it is a gas it escapes from the container and diffuses into the atmosphere.

The loss of mass from the container is measured straight with the analytical residual.

Process:

Refer to the electronic rest users guide to set upward the balance. Be sure to level and zero the unit.
Put about 50 mL of h2o in the beaker, using the graduations on the beaker.
Break the tablet into quarters. Yous need non exist accurate.
Cut a square of the plastic sufficient to embrace the beaker loosely, assuasive gases to escape but retaining water spray. This keeps the h2o there to exist massed, and prevents spray from dissentious the residue.
Place the beaker and plastic on the balance. Close the door. Practise non put the tablet in the residue all the same!
Press the Tare button to zero the balance. This will allow the balance to directly read out the mass of the tablet afterwards it is placed on the balance.
Open up the door, place the Alka-Seltzer on top of the plastic, and close the door.
Tape the mass of the tablet from the display.
Open the door and allow the quarter tablet to drop into the water. Replace the plastic on the beaker and shut the door. The mass displayed volition begin to dropas the gas is liberated and dissipated. The display shows the loss of mass of the tablet, which is equal to the mass of the gas liberated. After a fourth dimension, the brandish will slow downwards, but in a 3-hr timeframe it won't stop completely. Tiny bubbles will still be observed in the h2o as carbon dioxide continues to come out of solution. You have to brand a determination of the signal at which you wish to consider the experiment completed. It might be helpful to the students to tape data at regular fourth dimension intervals and then to graph the mass lost versus time.