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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: kdbmvp on February 14, 2019, 05:05:59 AM

Title: Precipitation reaction
Post by: kdbmvp on February 14, 2019, 05:05:59 AM

Hello,

I have a question regarding precipitation reactions. Consider the following rx:

Pb(NO₃)₂ + 2NaOH -> Pb(OH)₂+ 2Na⁺ + 2NO₃^-

My question is: Why doesn't the 2Na⁺ cations react with the 2NO^- anions, but remain spectator ions?

Title: Re: Precipitation reaction
Post by: chenbeier on February 14, 2019, 05:15:18 AM

First there will be no NO^-.

If you dissolve Pb(NO₃)₂ and NaOH seperatly in one beaker glass then you get Pb²⁺ and 2 NO₃^- and in the other glass Na⁺ and OH^-.

If you now mix both solution the lead hydroxide Pb(OH)₂will precipitate . The Na+ and NO₃^- will be still dissolved in the solution. There for we call them spectator ions.

Title: Re: Precipitation reaction
Post by: kdbmvp on February 14, 2019, 05:23:02 AM

Sorry about that, writing mistake. Meant NO₃^-. But why doesn't Na⁺ and NO₃^- react? What determines this?

Title: Re: Precipitation reaction
Post by: chenbeier on February 14, 2019, 05:31:52 AM

They still swimming in the solution. Sodium nitrate is good solouble. If you evaporate the water you will get NaNO₃.

I tis the same you dissolve NaCl. You get Na⁺ and Cl^-. You get the salt back, if the water is removed.

Title: Re: Precipitation reaction
Post by: kdbmvp on February 14, 2019, 05:57:10 AM

Thank you!