Baking Soda and Hydrochloric Acid
Purpose:
Student will experimentally determine the mass of product produced in a chemical reaction. Student will compare theoretical values for the reaction to the experimental values obtained.
Introduction:
This is another stoichiometry lab … with the same purpose, but very different procedure when compared to the copper(II) sulfate and iron metal lab.
When performing an experiment involving chemical reactions, the scientist can theoretically determine how much of a product should be produced. S/He will make use of the fact that the coefficients of the reactants and products in a chemical equation represent the relative number of moles of each reactant and product involved in the reaction. From this information, the masses of products produced can be calculated. You will notice that when balanced using the simplest whole-number coefficients, the ratio(s) are 1:1:1:1:1
In this experiment you will react baking soda (a.k.a. sodium bicarbonate or sodium hydrogen carbonate) with hydrochloric acid solution converting the baking soda into table salt (NaCl), water and carbon dioxide gas (CO2). Evaporation will be used to separate the water from the salt.
NaHCO3(s) + HCl(aq) CO2(g) + H2O(ł)+ NaCl(aq)
sodium hydrogen carbonate
(a.k.a. sodium bicarbonate, or baking soda)
So you are asked to understand that the sodium chloride has be hydrated by the water. The ionic bond has been disrupted and the water molecules prevent the electrolytes from re-bonding. However, once the water of a mixture is evaporated, the dissolved solute(s) are left behind.
The mass of salt (sodium chloride)
produced will be determined.
Procedure:
1) Mass an empty evaporating dish. Record the mass to 0.001 g.
2) Now, on top of the evaporating dish, place a watch glass. Measure the dish and watch glass to 0.001 g.
3) Remove watch glass from the evaporating dish. Tare the balance (again!)…and add, to the evaporating dish
approximately2.000 grams of NaHCO3(s). Record the mass of the baking soda to 0.001 gram.
4) Move the whole system; evaporating dish, watch glass and baking soda to your lab station.
5) Using a clean graduated cylinder obtain approximately 10.0 mL of 3 MHCl(aq). Pour these 10.0 mL or so of
HCl into a small beaker … It will be easier to take aliquots of the acid, using the pipet, out of the beaker.
6) Set up your ring stand, ring clamp and wire gauze. Place the evaporating dish with the baking soda and
evaporating dish on the wire gauze/ring clamp.
7) Using the Beral pipet, feed HCl(aq) into the evaporating dish through the spout/lip. (To have enough room,
you may need to lift the watch glass just a touch… Try to keep the dish covered with the watch glass to
prevent splattering as best as is possible. (Add all of the HCl. Get a few mL more, should there not be
enoughto completely react all the of the sodium hydrogen carbonate. Keep adding HCl until no solid is left
and no bubbles are formed.
9) Once the reaction has ceased, put a meker burner beneath the system … light it and gently heat the system of
chemicals to dryness.
9) Allow the system to cool completely. Mass the evaporating dish, watch glass and salt to 0.001 g.
Questions:
1) Based upon your mass of baking soda, how much salt should you theoretically produce?
2) What is your per cent error between this theoretical value and the amount of salt actually produced?
3) How might the concept of “heating to a constant” mass be employed in this lab?
4) What might be sources of error?