Conductivity of barium hydroxide and sulfuric acid

[simmy]

I have a question I'm finding hard. Does anyone know?

What would you observe and what would happen to electrical conductivity when you slowly add sulfuric acid to an aqueous solution of barium hydroxide?

[NanoMachine]

This is an acid + base reaction.

sulfuric acid + barium hydroxide --> barium sulfate + water

The barium sulfate formed is insoluble. Conductivity is high at first because the barium hydroxide contains lots of ions including the fast moving hydroxide. Addition of sulfuric acid causes the barium ions to be removed to form barium sulfate. The hydroxide ions are also reduced in number because they join with H⁺ ions from the acid to form water. The result is water containing an undissolved, white solid. After the neutral point the number of ions begins to increase again because you're adding H⁺ ions and sulfate ions.

[y-axis]

Neat graph Nanomachine.

[simmy]

Great answer, thanks Nanomachine!

If you were gradually adding magnesium metal to sulfuric acid, what do you think the conductivity would do?

[KathChem82]

Magnesium reacts with sulfuric acid to produce magnesium sulfate and hydrogen gas.

Mg + H2SO4 -------> MgSO4 + H2

If the reaction vessel is not closed, hydrogen gas escapes to the atmosphere, leaving behind the MgSO4. You can determine if the solution will still conduct electricity if you know the properties, most especially the solubility, of magnesium sulfate. MgSO4 is a very soluble salt. It ionizes into Mg+2 and SO4-2 in the solution. Therefore, the solution still conducts electricity.

Cheers!

[NanoMachine]

Originally Posted by simmy

Great answer, thanks Nanomachine!

If you were gradually adding magnesium metal to sulfuric acid, what do you think the conductivity would do?

Sulfuric acid contains H⁺ and SO₄^- ions. When it reacts with Mg, you get Mg²⁺ and SO₄^- ions. The net effect is to replace H⁺ ions with less mobile Mg²⁺ ions. This lowers the conductivity of the solution. As you keep adding Mg the conductivity falls until all the acid has reacted and then straight lines as you can see in the graph below.

[simmy]

Another cool graph!! I was like KathChem and thought the conductivity wouldn't change. But I wasn't sure. Would never have thought it would look that shape. Thanks again Nano.