Introduction:
Ionic compounds in aqueous solution dissociate into its component ions. When two ionic compounds in aqueous solution are mixed together, the dissociated positive ions and negative ions combine to form new products in a double replacement reaction. If the product does not dissolve in aqueous solution, then the product forms an insoluble precipitate, a solid that does not dissolve in a liquid solution. If the product is soluble, then the ions remain dissociated in the solution and are known as spectator ions.
Purpose:
To observe chemical reactions involving the double replacement of ions and to write net ionic
reactions based on the results of the experiment. Ideally if no contamination occurs, the results of the
experiment should parallel the theory of the established solubility rules.
Materials:
Transparency and 4 sets of 0.10M solutions in small bottles of the following:
Silver nitrate AgNO3 Sodium Carbonate Na2CO3 Calcium Nitrate Ca(NO3)2
Potassium Phosphate K3PO4 Sodium Acetate NaC2H3O2 Zinc (II) Nitrate Zn(NO3)2
Potassium Bromide KBr Potassium Chromate K2CrO4 Iron (iii) Chloride FeCl3
Aluminum Nitrate Al(NO3)3 Ammonium Sulfate (NH4)2SO4 Lead (II) Nitrate Pb(NO3)2
Sodium Hydroxide NaOH
Safety:
Wear lab safety goggles and aprons. Wash all spills with plenty of water. * See MSDS for safety of chemicals!
Disposal:
Wash the transparency in the sink with plenty of water.
Pre-lab Questions:
- Where do you expect to observe precipitates? In the data table (back side of this lab paper), place a small “x” in the upper left hand corner of the appropriate boxes to indicate where you expect to observe precipitates according to the solubility rules. Also write the formula of the precipitate you expect to see in the upper right-hand corner of the box.
- Copy down the exact data table in your lab report (it has to look the exactly the same – it must fit on only ONE lab sheet). Write the formula of the precipitate that you expect to see form according of the solubility rules in the upper right-hand corner of the appropriate box. Make sure to leave enough room for observations in the data table (see Procedure #3). [Don’t forget to do an initial observation table of the reactants BEFORE you mix them!]
Procedure:
- Obtain the necessary pipets and a transparency.
- Place the transparency on the chart and carefully add one drop of each chemical in the appropriate square. Be sure that the tips of the pipets do not touch the surface of the transparency or any other solution in order to avoid contamination.
- After placing the solutions in each box (may need to wait about 30 seconds), record your observations in each box of your data table. For some reactions you may want to remove the white chart and use the black lab table as your background in order to observe the colors better. For observations, specify the following in this order:
a.) the color or if no color – write “colorless”
b.) opaque, cloudy, or transparent/clear
c.) presence of a precipitate; write “i” for insoluble
d.) absence of a precipitate; write “s” for soluble
- it may be helpful to make a key/legend on the bottom right-hand corner of the lab sheet.
- Wash the transparency in the sink, completely dry the transparency, and return it to the appropriate place.
- Clean up. Wipe and dry the lab table. Push stools under the lab tables. Wash your hands.
Data Analysis:
Write the balanced net ionic reaction for each observed and expected reaction. Do not include states of matter. Write all equations in a column and in order as follows: Number each equation. First write net equations for AgNO3 as it reacts with the reagents listed across the horizontal row. Then write net ionic equations for Na2CO3 as it reacts with the reagents across the horizontal row. Then write net ionic equations for Ca(NO3)2 as it reacts with chemicals across the horizontal row. Continue writing equations for the remaining reagents down the column as they react with reagents across the horizontal row. If observations did not conform to the theory of solubility rules: place a star () in the box and next to the written equation if a precipitate was supposed to form but was not observed; place a diamond (•) in the box and next to the written equation if a precipitate was not supposed to form and it did (for these, write the balanced molecular equation with phases since there isn’t a net ionic reaction).
Error analysis:
Number and list reactions that did not conform to the solubility rules ( & •). Discuss possible reasons that expected precipitates were not observed and why unexcepted precipitates formed in addition to sources of error.
Conclusion:
(answer these questions instead of the regular conclusion in the lab report guidelines handout)
Summarize the purpose of this experiment. State the four indications which indicate that a chemical reaction has occurred and state which indications of the four were most commonly observed in this lab. State if all of observations conform to the theory of solubility rules. Also summarize possible sources of error/contamination. If all of the reactions conformed to the theory of solubility rules, then state your success with the experiment.
NaC2H3O2 Pb(NO3)2 Al(NO3)3 (NH4)2SO4 NaOH FeCl3 K2CrO4 Zn(NO3)2 KBr K3PO4 Ca(NO3)2 Na2CO3AgNO3
Na2CO3
Ca(NO3) 2
K3PO4
KBr
Zn(NO3) 2
K2CrO4
FeCl3
NaOH
(NH4) 2SO4
Al(NO3) 3
Pb(NO3) 2
Data Table: Net Ionic Reactions