Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Shadow on January 30, 2014, 08:16:04 AM
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What is the chemical equation of the reaction of Lithium and diluted sulfuric acid? What's the reaction with concentrated sulfuric acid? I think that in one situation sulfur dioxide will be produced and in another hydrogen, but I am not sure which in which one. Need help for deducing this.
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Let's start with something simpler - how do the alkali metals react with water?
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I know that, hydrogen reduces to gas, and alkali is produced.
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OK how does an acid and alkali react?
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Wasn't that my original question? I read somewhere that in diluted solutions hydrogen gas will be produced, and in concentrated sulfur dioxide, but why is it so? I need the reasoning behind this, not to write simple equations.
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Wasn't that my original question?
No. Lithium is not a base, it is a metal.
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I thought that he mean alkali metal. Why is this relevant? It would be just neutralization (base+acid). Again, what happens when lithium react with dil. or conc. sulfuric acid?
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OK, let's try from different direction. How do the metals react with acids in general?
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I can't generalize that. If a transition metal react with e.g. nitric acid of different concentrations, a complex mixture of gasses is produced. In the case I am interested in, there are two possibilities. Only what I can say is that the metal gets oxidized and that hydrogen or another element composing the acid can get reduced.
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If I may chip in here. Is water behaving like an acid in its reaction with an alkali metal such as lithium?
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No, isn't it redox reaction?
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Sure it is a redox reaction. We are back to the starting point - how do metals react with acids in general?
To point you in the right direction: metal gets oxidized. What is the oxidizer?
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Again, either hydrogen or another element with a high oxidation state that composes the acid. Which will be the oxidizer in conc. and which one in dil. solutions?
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Again, either hydrogen or another element with a high oxidation state that composes the acid.
And what does it depend on? Have you heard about reactivity series?
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DIdn't, but I read in wikkipedia about it, Li is very reactive, but there wasn't a word about change of acid concentration.
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Acid concentration wasn't mentioned, because in general it is a secondary thing.
Do you know now which metals will reduce the acid to the oxide (and why)?
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The less reactive metal. Sulfate is easier reduced than hydrogen. What happens if we put into the concentration factor?
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Sulfate is easier reduced than hydrogen.
Not exactly. That's where the concentration comes into play.
Let's take a less reactive metal like copper. It doesn't dissolve in diluted sulfuric acid, because H+ is not and oxidizer strong enough. However, in concentrated solutions, and in the low pH (which is typical in concentrated acid solution), SO42- becomes a relatively strong oxidizing agent:
SO42- + 4H+ + 2e- :rarrow: SO2 + 2H2O
and it can oxidize copper producing SO2. Note SO42- is not an oxidizer without H+, it is quite stable and inert.
When it comes to lithium, it is so reactive it will be oxidized even by water alone, no need for any acid (technically, as water dissociates into H+ and OH-, we can assume there is always an acid present in water). When you add sulfuric acid, it doesn't have to behave like a strong oxidizer, there is plenty of H+ and water that will easily react with the lithium itself, producing hydrogen.
I suppose in the case of concentrated sulfuric acid some SO2 can be produced by side reactions, but I would not expect it to be the main product.