2-3: Strong and Weak Electrolytes 1. Start Virtual ChemLab and select Strong and

Question

2-3: Strong and Weak Electrolytes 1. Start Virtual ChemLab and select Strong and Weak Electrolytes from the list of assignments. The lab will open in the Titration laboratory. 2. Enter the stockroom by clicking inside the Stockroom window. Once inside the stockroom, doubleclick or click and drag on the three reagents, NaCl, Na2CO3 (100%), and NaHCO3 (100%) to move them to the stockroom counter. Click on the green Return To Lab arrow to return to the laboratory. 3. For each salt that was selected in the stockroom, complete the following procedure: double-click or click and drag the bottle on the stockroom counter to move it to the spotlight next to the balance. Click on the Beakers drawer and place a beaker in the spotlight next to the salt bottle in the balance area. Click on the Balance area to zoom in and open the bottle by clicking on the lid (Remove Lid). Drag a piece of weighing paper and drop it on the balance and then Tare the balance. Pick up the Scoop and scoop out some sample by first dragging the scoop to the mouth of the bottle and then pulling the scoop down the face of the bottle. As the scoop is dragged down the face of the bottle it will pick up different quantities of solid. Select the largest sample possible and drag the scoop to the balance and drop it on the weighing paper. This will put approximately 1 g of sample on the balance. Now drag the weighing paper with the sample and drop it in the beaker. Click on the green Zoom Out arrow to return to the laboratory. Move the beaker to the stir plate. Pick up the 25 mL graduated cylinder near the sink and hold it under the water tap until it fills. Pour the water into the beaker by dragging and dropping the cylinder on the beaker. Turn on the conductivity meter located on the lower right of the table and place the conductivity probe in the beaker and record the conductivity of the solution in the data table below. Double-click on the salt bottle to place it back on the stockroom counter. Place the beaker in the red disposal bucket. Repeat for the other two reagents. 4. When you have completed the three reagents, return to the Stockroom. Double-click on each bottle to return it to the shelf. Obtain three more samples (two salts and one solution): KNO3, NH4Cl, and NH3 and return to the laboratory. Follow procedure #3 for NH4Cl, and KNO3. For the NH3 solution, complete the following procedure: Place a beaker on the stir plate. Pick up the NH3 solution from the stockroom shelf, drag it to the 25 mL graduated cylinder, and let go to fill the cylinder. The solution bottle will automatically go back to the stockroom shelf. Drag the 25 mL graduated cylinder to the beaker on the stir plate and drop it to transfer the solution into the beaker. Place the conductivity meter probe in the beaker and record the conductivity in the data table. 5. When you have completed the three reagents, return to the Stockroom. Double-click on each bottle to return it to the shelf. Obtain two more samples: HCl and HCN. Measure the conductivity of each solution following procedure #4 and record the conductivity in the data table. Data Table NaCl Na2CO3 NaHCO3 KNO3 NH4Cl NH3 Electrolytes are compounds that conduct electricity in aqueous solutions. Which compounds in your table are electrolytes? Which are not electrolytes? 7. Would any of these electrolytes conduct el ectricity in the solid form? Explain. 8. Are these ionic or covalent compounds? Classify each compound in the grid as ionic or covalent. For a compound to be an electrolyte, what must happen when it dissolves in water? 9. When an ionic solid dissolves in water, water molecules attract the ions causing them to dissociate or come apart. The resulting dissolved ions are electrically charged particles that allow the solution to conduct electricity. The following chemical equations represent this phenomenon: NaCl (s) = Na+(aq) + Cl (aq) Na2 CO3 (s) = 2Na + (aq) + CO32-(aq)

Explanation / Answer

Of the given compounds,

Electrolytes : NaCl, Na2CO3, Na2CO3, NaHCO3, KNO3, NH4Cl

Non-electrolytes : NH3

The ones which conduct electricity are : NaCl, NaHCO3, KNO3, NH4Cl

None of the compounds would conduct electricity in solid form

Classification of compounds,

Ionic : NaCl, NaHCO3, KNO3, NH4Cl

Covalent : Na2CO3, NH3

For compounds to conduct electricity, they must dissociate into ions in solution

Dissociation equations,

NaCl --> Na+ + Cl-

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