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GRADE 11 & 12- CHMISTRY
INVESTIGATION Strength of Electrolytic solutions
Challenge
Test various concentrations of electrolytic solutions in order to determine the
relationships among degree of dissociation, solute concentration, and electrolytic
strength.
1.0Equipment and Materials
• Copper wire with crocodile clips
• Cardboard or foam board
• Two carbon electrodes
• Plastic containers 2
• 100 ml of each of the following type of test solutions
• wash bottle and waste container
• Multimeter ( 0.3mA- 300mA) find the uncertainty of the instrument ?
Following solutions (in 150-mL beakers):
1) 0.5 M hydrochloric acid (HCl)
2) 0.5 M acetic acid (CH3CO2H)
3) 0.5 M ammonium hydroxide (NH4OH)
4) 0.5 M calcium hydroxide (Ca(OH)2)
5) Tap water
6) 0.5 M ammonium chloride (NH4Cl)
7) water, distilled
2.1 Safety Precautions
Handle solutions carefully! Concentrated acids and bases
can burn skin. Wear gloves and lab aprons and clean up
spills with care. Avoid breathing fumes from any of the
test solutions.
Wear safety glasses and follow standard laboratory
safety procedures.
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2.2 Background
Electrolyte solutions conduct electrical current due to the presence of charged
particles, or ions, in the solution. [Charged particles are created when a
substance either dissociates in or reacts with the solvent (usually water) to form
ions.] The more ions the solution contains, the greater the amount of electrical
current the solution can carry—in other words, the better a conductor it is.
Substances that dissolve to form good conductive solutions are called strong
electrolytes. They are usually ionic compounds, breaking apart when dissolved to
exist in their ionized form. As a result, the solution contains no intact ionic
compounds, only free ions. Since measuring a solution’s conductivity gives an
indication of the number of ions in the solution, a high conductivity reading
indicates a strong electrolyte. Some molecular compounds, notably acids and
bases, can also form solutions with high conductivity, because when dissolved
they react with the solvent to form ions. Instead of a simple dissociation, the
chemical reaction produces the charged particles. A solution of hydrochloric acid
in water is one such example:
Substances that tend to ionize completely include strong acids, strong bases, and ionic
compounds (salts).
Substances that are weak electrolytes are molecular compounds that dissociate
only partially in solution. When dissolved, a limited number of ions do form, but
intact molecules also exist to some degree in the solution. The solutions formed
by weak electrolytes are poor conductors of electricity. Because fewer ions are
present, measurements of their conductivity will be lower than for solutions of
strong electrolytes.
A substance can only form ions in solution if it first dissolves, so any electrolyte
(strong or weak) must be at least partially soluble—that is, able to be dissolved by the
solvent. However, there are substances that dissolve without forming anyions. These
substances are soluble but are nonelectrolytes. What do you think the conductivity of
such a solution would be?
What if a substance is only partially soluble—in other words, it does not dissolve
well? It may still be a strong electrolyte, if the amount that can dissolve dissociates
completely. Although only a small amount of the substance dissolves,
if that amount exists solely as ions, the substance is still classified as a strong
electrolyte. Some salts, such as barium hydroxide, fall into this category. Because
Ba(OH)2 is only slightly soluble in water, a concentrated aqueous solution cannot be
made, but a dilute aqueous barium hydroxide solution will still conduct electricity due to
the presence of Ba+ and OH- ions.
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2.3 Equipment set up
2.3.1 Connect the electrode as per the fig1.
2.3.2 Negative lead connect to negative terminal of the dry cell battery .connect switch
closer to negative electrode.
2.3.3 Connect multimeter terminal to positive terminal of the battery
2.3.4 Finally connect the remaining terminal of the meter to positive electrode .as per fig
2
Multimeter
Battery
Make
contact
switch
Carbon
Electrode
Electrolytic
solution
Circuit diagram
Fig 2
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2.3.5
2.3.6
2.3.7
2.3.8
2.3.9
Pour 50ml of the solution in to the plastic container.
Male the switch on and complete the electrical circuit .
Record the ammeter reading .
Clean the plastic container with distilled water .
Step 2.3.5 to 2.3.8 with 6 different solutions .
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