Download Lab: Chemical Reactions I

Lab: Chemical Reactions I
Objectives
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Understand qualitative tests for ions that are based on solubility
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Learn that Na+, SO4- and Na2CO3 are water soluble
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Recognize balanced chemical equations
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Perform a qualitative experiment with aqueous solutions
Introduction
Many of us remember those tearful
moments in the bath when soap got in our
eyes. We use soap everyday to wash our
skin, hair, clothes, cars, pets, and other
products. In fact, people have produced
and used soap for more than 5000 years. It
was one of the first applications of mixing
different chemicals to produce a new
product. What is soap and how is it made?
The process of making soap involves the
combination of two different types of
substances: fats (either animal fats or plant
oils) and lye (sodium hydroxide). In ancient
times, lye was produced in a variety of
ways, but usually involved leaching salts
from plant ashes, such as wood-ash to
extract potash (potassium carbonate) or soda
ash with lime (calcium oxide) produces lye.
Figure 1: Samples of a variety handmade Italian
soaps. The ancient Egyptians, Germans, and
Romans used soaps to wash their hair, bodies,
and clothing as early as 2000 BC. Making soap
is a simple process and many fine soaps are still
crafted by hand.
ash (sodium carbonate). Combining soda
Many types of chemical reactions occur naturally and chemists use them to produce a
variety of substances or to perform analysis. A precipitation reaction produces a solid
substance when two or more liquid (aqueous) solutions are mixed together. The solid
forms when one ion replaces another ion. A precipitation reaction is one way that
© KC Distance Learning chemists analyze an ionic compound to determine the presence of certain water soluble
ions, such as Ca2+ or Mg2+.
Sodium carbonate (soda ash) Na2CO3 is a
polyatomic compound that is water soluble,
much like many nitrates, acetates, and
ammonium ions. Another water soluble
polyatomic compound is Epsom salt,
known chemically as magnesium sulfate
(MgSO4). Mixing these two aqueous
solutions can free the soluble ions and
result in the precipitation of non-soluble
solids.
Figure 2: A molecular model of sodium carbonate.
Sodium carbonate has many uses, including: use
as a water softener, producing glass, bleaching
skeletons for display, bonding dyes to fibers,
preserving foods, cleaning silver, and in toothpaste
as a cleaning agent.
Chemists use chemical equations to
predict and record the events that occur in
a chemical reaction. The chemicals that
are combined together and react are
referred to as the reactants and are placed
on the left hand side of the equation. The
chemicals that are produced are placed on
the right hand side of the equation and are
referred to as the products. The equals
sign in the equation is replaced with an
arrow to illustrate the direction of the
reaction.
The reaction you will be observing in this lab is written in the following fashion:
+
-
MgSO4(aq) + Na2CO3(aq) → 2 Na(aq) + SO4(aq) + MgCO3 (s)
The abbreviations (aq) and (s) represent aqueous and solid, respectively. Aqueous
means that the substance has been dissolved in water. This chemical equation is
balanced to represent the conservation of matter. The number 2 in front of the sodium
ion is referred to as a coefficient and is placed there by the chemist to make sure that
the equation is balanced (the same amount of each element before and after the
reaction).
© KC Distance Learning Pre-lab Questions
1. Which chemical, originally produced from the ashes of plants, is essential for
making soap?
2. What has happened to a chemical that is in an aqueous form?
3. What is one type of reaction that can be used to find soluble ions?
© KC Distance Learning Experiment: Precipitation of a Solid
In this experiment, you will be working with two aqueous substances to produce a
reaction that will cause a precipitate to form.
Materials
Safety Equipment: Goggles or glasses, gloves, apron
• Powdered laundry detergent (1 teaspoon)
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(must contain washing soda or soda ash)
Epsom salts (Magnesium sulfate), MgSO4
Measuring spoons
Pure water (warm)
4 plastic cups (clear)
Food coloring (red and blue)
Eye dropper or straw
Permanent marker
Procedure
1. Warm (do not boil) 2 cups of the distilled water in a microwave oven.
2. Label your plastic cups: LD solution, ES solution, ES test solution, LD test
solution.
3. Dissolve 1 teaspoon of laundry detergent with ½ cup of warm water in the plastic
cup labeled “LD solution.” Stir until the solid is completely dissolved.
4. Dissolve 1 teaspoon of Epsom salts with ½ cup of warm water in the plastic cup
labeled “ES solution.” Stir until the solid is completely dissolved.
5. Dissolve 1 tablespoon of Epsom salts with 2 tablespoons of warm water in the
plastic cup labeled “ES test solution.” Stir until the solid is completely dissolved.
6. Add a few drops of blue food coloring to the ES test solution.
7. Dissolve 1 tablespoon of laundry detergent with 2 tablespoons of warm water in
the plastic cup labeled “LD test solution.” Stir until the solid is completely
dissolved.
© KC Distance Learning 8. Add a few drops of red food coloring to the LD test solution.
9. Use an eye dropper or straw (with your finger on the end) to collect a few drops
of LD test solution.
10. Observe what happens as you drop the LD test solution into the Epsom salt
solution.
11. Use an eye dropper or straw (with your finger on the end) to collect a few drops
of ES test solution.
12. Observe what happens as you drop the ES test solution into the laundry
detergent solution.
13. Record your observations.
14. Dispose of your chemicals by washing them down a sink.
15. Clean your work area.
16. Wash your hands.
Data and Observations
Red LD test solution added to Epsom salt solution:
Blue ES test solution added to laundry detergent solution:
© KC Distance Learning Post-lab Questions
1. Could the two aqueous solutions be identified through a visual inspection? Explain.
2. What happened when a drop of the sodium carbonate solution was mixed with the
magnesium sulfate?
3. Which solid substance contains magnesium (Mg)?
© KC Distance Learning