Page 1               LAB – First Law of Chemistry – Conservation of Mass 

Discovered by Lavoisier  (to be done with Ch 3.2)   Std 3a


Name: ___________________________                       Lab Station / Group # ________

Period: ________                                                            Date: ________________


Purpose:   Observe both endothermic and exothermic reactions.  Mix the reactants (each in their own corner of a plastic bag) of this chemical reaction together with a diluted phenol red solution.  Observe the reaction and record everything you see.  Practice writing a procedure.  Learn the “First Law of Chemistry” (conservation of mass  Massreactants = Massproducts )  through first  hand experience.



chemicals:     sodium hydrogen carbonate (NaHCO3)   9 g ± 0.5 g

                     anhydrous calcium chloride (CaCl2 )     7 g ± 0.5 g

                     diluted phenol red solution (1:10 dilution with H2O)  8.5 mL ± 1 mL

                           (red if in base  -  yellow if in acid)

equipment:   centigram balance

                     1 qt Ziploc plastic bag (reaction bag)

                     10 mL graduated cylinder

                     masking tape (for labeling things)

                     filter paper



Chemical reactions being observed:

   Mimics you stomach making acid

   2 NaHCO3 (aq) +  CaCl2 (aq) +  H2O (l)  ---->  CaCO3 (s) +  2 NaCl (aq)  + H3O+ (aq) (exo)

   Mimics you taking sodium bicarbonate for excess stomcach acid

                        H3O+ (aq)   + NaHCO3 (aq)   ---->  CO2  (g)  +  H2O (l)  +  Na+ (aq)     (endo)


NOTE:         Share responsibilities within your group.  Everyone should have a job.  Use filter paper on the pan to weigh out your dry chemicals.  Never put chemicals directly on the chrome pan of the balance.



You will write your own procedure.  The data table below may be helpful.  Your procedure must include step-by-step directions on how you will weigh out  NaHCO3 with CaCO3 and place them in opposite ends of a plastic Ziploc bag .  10 mL of  diluted phenol red must be poured into the bag to mix your chemicals so that the bag doesn’t lose any gas that is produced.  You will have to consider safety precautions for what you will do if too much CO2 (g)  is formed for the bag to hold. 

Page 2



You set up your own observation section that must include:

            1.  temperature – as  felt with your hands at each end of the bag

                        Exothermic reactions produce heat. 

                        Endothermic reactions get colder (suck up heat). 

            2.  gas formation – where  & approximately how much

            3.  change or lack of change of mass for the bag with everything inside,  before and after the reaction.

            4.  color and texture of chemicals (dry & liquid)  before and after the reaction

            5.  every change that indicated a chemical reaction occurred at any stage of the mixing of the chemicals with the phenol red solution





                     DATA TABLE



masses   (to 3 decimals)

volumes (to 2 decimals)

plastic bag – grams


filter paper – grams


NaHCO3  9 g ± 0.5 g


CaCl2  7 g ± 0.5 g


10 ml grad cylinder - grams


diluted phenol red  8.5 mL ± 1 mL  - mass and vol.


mass of plastic bag with all chemicals (before readction starts) 


mass of plastic bag with all chemicals (5 min after reaction starts)