Question

conductivity and solubility many ionic compounds can dissolve in water. when an ionic compound dissolves, ions break away from the crystal as they are surrounded by water molecules. these ions are free to move in the solution. thus, the resulting solutions can also conduct electric current. when a voltage is applied, anions move toward the positive electrode and cations move toward the negative electrode. the movement of ions allows electricity to flow through the wires that connect the electrodes. liquid ionic compounds can also conduct electric current because the ions are mobile. melting point ionic compounds tend to be solids at room temperature because they have high melting points. for example, nacl melts at about 800°c, and mgo has a melting point greater than 2800°c. the melting points of ionic compounds tend to be high because it takes a large amount of energy to overcome the strong attractive forces that hold the ions together throughout the solid. sep plan an investigation suppose you have samples of three unknown solids. explain how you could use their properties to determine whether or not they are ionic solids.

Explanation:

Ionic compounds have high melting points and conduct electricity when dissolved in water or in liquid state. So, to determine if the unknown solids are ionic:

• Melting Point Test: Heat the solids. Ionic solids will have high melting points (e.g., NaCl melts at about 800°C).
• Conductivity Test: Dissolve the solids in water (if soluble) and check if the solution conducts electricity. Also, if possible, melt the solids (by heating to high temperatures) and check for electrical conductivity in the liquid state.

Answer:

1. Melting Point Test: Heat each unknown solid. If a solid has a high melting point (similar to known ionic compound melting points like NaCl’s ~800°C or MgO’s >2800°C), it could be ionic.
2. Conductivity Test:

• Aqueous Solution: Dissolve each solid in water (if soluble). Use a conductivity apparatus (like a battery - bulb - electrode setup). If the solution conducts electricity (bulb lights up), it may be ionic (as ions are free to move in solution).
• Liquid State (if applicable): If the solid can be melted (by heating to a very high temperature), check if the liquid conducts electricity. Ionic compounds in liquid state (where ions are mobile) conduct electricity.