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The Identity of an Insoluble Precipitate
Introduction
The properties of any substance depend in part on the chemical bonds that hold the atoms
of the substance together. The consequences of this dependence are very important in
chemical reactions. Because bonds are formed or broken during a reaction, the properties
of product molecules differ from those of reactant molecules. If there is a significant
difference, a distant signal that a chemical reaction has occurred can usually be observed.
One easily seen signal of a chemical reaction is the formation of an insoluble precipitate.
This experiment deals with a quantitative interpretation of a reaction in which this signal
has appeared.
In this experiment, you will examine the reaction between Ba(NO3)2 and NH2SO3H
(sulfamic acid) in a hot solution. The identity of the insoluble substance that results from
the reaction will be determined from mass relationships.
Concept of the Experiment
Known quantities of Ba(NO3)2 and NH2SO3H will be allowed to react in boing water.
Certain covalent bonds in the molecules of sulfamic acid will break slowly during this
reaction, and a polyatomic anion will be formed. This anion will combine with the Ba2+
cations from BA(NO3)2 to form an ionic substance that appears as a white precipitate.
The precipitate will be one of three possible compounds:
1. Ba(NH2SO3) (barium sulfamate)
2. BaSO4 (barium sulfate)
3. Ba(NH2)2 (barium amide)
You will determine which one it is from the masses of the precipitate and the limiting
reactant.
The Identity of an Insoluble Precipitate
Procedure
**NOTE: Use instructions provide by the instructor – DO NOT USE INSTRUCTIONS
IN CHEMLAB! To remove the instructions on the screen, and free-up more working
area, perform the following operation: click on the OPTIONS tab; then click on LAB
ONLY. The instructions “disappear” and all of the area is now lab space.**
Step 1: Fill 250 mL beaker with 1.3 gm of Ba(NO3)2 and 2.5 gm of NH2SO3H.
Step 2: Add 150 mL of water to the beaker; stir the contents. Add a thermometer to the
beaker.
Step 3: Prepare hot water bath by placing 400 mL of water in a 600 mL beaker. Add a
thermometer. Heat to boiling with a Bunsen burner.
Step 4: Select hot water bath and beaker that contains the sample. Select combine and
observe and note in the observations what happens (when the sample reaches 100ºC)
Step 5: Obtain a 250ml Erlenmeyer flask and add a Buchner funnel (right click on flask,
select Buchner funnel). Pour the contents of the beaker into the funnel. Remove the
Buchner funnel from the Erlenmeyer flask (again by right clicking on flask, selecting
Buchner funnel) and save the solid contents in a watch glass. Weigh the sample and
record the result.
The Identity of an Insoluble
Precipitate
Name:__________
Sect:____________
Observations
Data
Mass of Ba(NO3)2 (g) =
Mass of NH2SO3H (g) =
Mass of precipitate (g) =
Calculations
1. The following reactions, shown in unbalanced equations, are pertinent to this
experiment. Balance the equations.
Ba(NO3)2 (aq) +
NH2SO3H (aq) +
H2O (l) →
Ba(NH2SO3)2 (s) +
Ba(NO3)2 (aq) +
NH2SO3H (aq) +
H2O (l) →
BaSO4 (s) +
Ba(NO3)2 (aq) +
NH2SO3H (aq) +
H2O (l) →
Ba(NH2)2 (s) +
HNO3 (aq)
NH4NO3 (aq) +
HNO3 (aq)
H2SO4 (aq) +
HNO3 (aq)
2. Determine the limiting reactant in each of the following three reactions. Calculate the
number of moles of each reactant.
Reaction producing Ba(NH2SO3)2
Reaction producing BaSO4
Reaction producing Ba(NH2)2.
3. Calculate the expected masses of the three possible products. Use the mass of the
limiting reactant and the equations that you balanced.
Ba(NH2SO3)2
BaSO4
Ba(NH2)2.
4. Compare the mass of your precipitate with the masses obtained in question 4. Bases
on this comparison, what is the identity of the precipitate?
Questions
1. What is the electron-dot formula for NH2SO3H? The first two hydrogen atoms are
bound to the nitrogen atom, whereas the last hydrogen atom is bound to an oxygen
atom. Bonds between on oxygen atom and another do not occur in this compound.
2. What is the electron-dot formula for the anion in the precipitate?
3. What covalent bonds in the sulfamic acid an water molecules must have been broken
to form this anion? What bonds, if any, must have formed?
Discussion