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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: jcklwy on February 10, 2020, 12:06:46 AM

Title: Limiting Reagent in an experiment
Post by: jcklwy on February 10, 2020, 12:06:46 AM
In a reaction between mg and hcl, the magnesium is designed to be the limiting reagent. Why is this? Is the solid always the limiting reagent?
Title: Re: Limiting Reagent in an experiment
Post by: Borek on February 10, 2020, 03:41:22 AM
Quote from: jcklwy on February 10, 2020, 12:06:46 AM
In a reaction between mg and hcl, the magnesium is designed to be the limiting reagent.

Not necessarily. You can design an experiment this way, but it is not a must.

Most likely the experiment you have on mind was designed this way for some specific reason. Hard to tell not knowing details.

Quote
Why is this? Is the solid always the limiting reagent?

No. For example, if you use solid CaO to absorb CO2 from the flowing gas, you want to have an excess CaO to make sure none of the CO2 passed through.
Title: Re: Limiting Reagent in an experiment
Post by: kriggy on February 14, 2020, 02:52:42 PM
Its probably practical reasons: separating solid MgCl2 from HCl solution is fairly easy. Separating solid MgCl2 from solid Mg chunks is fairly complicated
Title: Re: Limiting Reagent in an experiment
Post by: Borek on February 14, 2020, 05:49:11 PM
Quote from: kriggy on February 14, 2020, 02:52:42 PM
Its probably practical reasons: separating solid MgCl2 from HCl solution is fairly easy. Separating solid MgCl2 from solid Mg chunks is fairly complicated

My bet is that the experiment in question is about measuring the yield of the hydrogen, if so selection of the limiting reagent is quite obvious.