Chemistry B- Conservation of Mass Lab
Name: ______________________ Hour: ______
We have learned our symbols which represent the elements, and to write formulas which represent chemical
compounds. Now we are ready to write equations to represent chemical reactions. In this exercise we are
going to investigate the mass of a system before and after a chemical reaction has taken place. In this particular
reaction the reactants are all liquid, while one of the products in a solid. When a reaction produces a solid
product we refer to the product as a precipitate.
Pre-Lab Questions
1. Define the following terms in your own words:
a. soluble _________________________________________________________________________
b. insoluble _______________________________________________________________________
c. precipitate _______________________________________________________________________
2. a.
The starting materials in a chemical reaction are called ______________________________
b. The ending materials in a chemical reaction are called _______________________________
c. An arrow in a chemical equation means ________________________
3. a. chemical symbols are used to represent ____________________________________
b. chemical formulas are used to represent ____________________________________
c. chemical equations are used to represent ___________________________________
Procedure
1. Your lab station has a stoppered Erlenmeyer flask containing a small vial and a 50 mL graduated
cylinder. Remove the vial from the flask.
2. Measure 25 mL of copper (II) nitrate solution using the graduated cylinder and then pour this solution
into the Erlenmeyer flask.
3. Fill the vial approximately 2/3 full of the sodium carbonate solution and wipe any spills off the outside
of the vial.
4. Carefully slide the vial down into the flask, on an angle, don’t drop it into the flask so that it punches a
hole in the bottom. The vial should rest upright in the flask and the two solutions should not mix.
5. Stopper the flask and then use your triple beam balance to measure the mass of the whole system. Be
sure to read your balance to two places after the decimal and record a unit after the number. NO naked
numbers!
6. Now carefully invert the flask so that the two solutions are mixed. Carefully examine the system and
look for evidence of a chemical reaction.
7. Measure and record the mass of the whole system after the reaction.
8. Add a little water and rinse as much of the solid as possible into the bucket on the back lab table that is
labeled waste chemical. Wash and dry the flask and vial and leave them in good condition for the next
hour. Wipe the lab table clean so it is clean and dry. Make sure your balance is clean and dry and all
of the masses are back to the zero position.
9. Be sure to wash and dry your hands with soap and water after completing the lab – these chemicals are
poisonous.
Data
Mass of flask, stopper, and chemicals before the reaction
________________________(units)______
Mass of flask, stopper, and chemicals after the reaction
________________________(units)______
Chemistry B- Conservation of Mass Lab
Name: ______________________ Hour: ______
Questions
1. What evidence did you observe that suggested a chemical change had occurred?
2. What is the definition of the word precipitate (in your own words)?
3. How did the mass of your products compare with your mass of your reactants?
4. Use your packet and look up the Law of Conservation of Matter and state it here.
5. How closely do your results agree with the Law of Conservation of Matter? If they do not agree, what
reasons can you suggest for the disagreement?
6. Write a word equation for the reaction you observed. Write the names for the reactants (look back in the
procedure!) and the names of the products formed (copper (II) carbonate and sodium nitrate).
_______________________________ + ________________________________ yields
_______________________________ + ________________________________
7. Now write the same information but this time using formulas instead of names. This the called the skeleton
equation.
_________________ + _________________  _________________ + _________________
8. Now compare the numbers of atoms of each type on the reactants side of the equation (left) and the
products side the of the equation (right) in the equation you write in question #7.
# of atoms on left
_______ Cu ________ N ________ O ________ Na ________ C
# of atoms on right _______ Cu ________ N ________ O ________ Na ________ C
9. Notice that the equation is not balanced. We do not have the same number of atoms of each type on both
sides of the equation. Insert a coefficient in front of the sodium nitrate to make the equation balance
when you rewrite the equation below. An equation is not correct or true until it is balanced.
_________________ + _________________  _________________ + _________________