In this lab students will demonstrate how stoichiometry can be applied to a chemical reaction that produces a gas.
Other chemicals will react with an acid in the same way. These chemicals are known collectively as carbonates. Here are a few examples of carbonates: caclium carbonate (a.k.a. chalk), sodium carbonate (a.k.a. washing soda), and sodium bicarbonate (a.k.a. baking soda). In this lab you will write and balance an equation for the reaction of sodium carbonate with hydrochloric acid. The products will be the same (with the exception of the ionic compound that forms) as for the reaction shown above.
In the chemical equation above the notation (aq) means ‘aqueous’, that is, dissolved in water. The notation (s) means solid and (g) means gas. These notations are included to show that a gas forms in the reaction. A gas will bubble up and out of the reaction mixture and cause it to have a smaller total mass than it did before the reaction.
Stoichiometry is the technique of using the molar ratios in balanced chemical equations to calculate the amount of reactants or products. In this lab you will take a known amount of hydrochloric acid and react it with excess sodium carbonate. By using molar ratios from the balanced chemical equation you will be able to predict the amount of carbon dioxide that will form. Then you will perform the reaction in the lab in such a way as to measure how much carbon dioxide is produced. If all goes well then the numbers should be very close to one another. Specifically, you should find that your measurement is within a half a gram or less of your prediction.
You will work with one partner on your plans. Then you will get together with another pair of students to carry out the reaction and perform the experiment. The data will be gathered together by your teacher so that the class will be able to produce a total of four or five trials total.
In your lab notebook write and balance the chemical equation that describes the reaction between sodium carbonate and hydrochloric acid. Use the equation written in the Overview as a model and be sure you have correct chemical formulas before you balance the equation. Compare your work with your lab partner’s.
The 50 mL of hydrochloric acid solution, if measured very precisely, contains 3.5 g of HCl. In your lab notebook use this information to predict the mass of carbon dioxide that will be produced when this amount of acid reacts. Work with your lab partner to carry out this calculation correctly. Share your result and show your work to your teacher for approval before moving on.
Gather the items in the materials list except the chemicals—get them just before you’re ready to use them. You will have to use appropriate equipment to measure the sodium carbonate and the hydrochloric acid.
Set up the equipment you have to carry out this chemical reaction in such as way as to be able to measure the amount of carbon dioxide produced. Discuss this with your group and come up with a plan and write it in your lab notebook. Share this written plan with your teacher for approval before carrying out your plan. Here is an important tip: Do not add all of the acid at once or it will bubble over the top of the flask and ruin your experiment.
Carry out your plan and observe the reaction closely. Record your observations in your lab notebook. Be careful to examine the flask carefully both during and after the reaction. Note changes in appearance, mass, temperature and whether or not all of the solid dissolves.
Measure the amount of carbon dioxide produced. Record it in your lab notebook and show work for the calculation that you used to measure the amount of carbon dioxide. Share the result with your teacher so the results can be shared with the rest of the class. When you have the opportunity, obtain the results of the other groups in your class and record them in your lab notebook.
In a Google Doc submitted through Classroom, answer the following questions as an individual. You may not work with a partner to answer the questions and your responses will be graded based on their accuracy.