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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Veef on January 06, 2021, 01:54:32 AM

Title: Literally no one can answer this. PLEASE EXPLAIN WHY.
Post by: Veef on January 06, 2021, 01:54:32 AM
One mole samples of each of the solid carbonates of lead, calcium, barium and magnesium are reacted in turn with excess dilute sulfuric acid.

Which sample of carbonate will release the greatest volume of carbon dioxide?

A barium

B calcium

C lead

D magnesium

answer is D
Title: Re: Literally no one can answer this. PLEASE EXPLAIN WHY.
Post by: AWK on January 06, 2021, 02:07:05 AM
If the correct answer is d then you are giving the wrong question.
1 mole of each of these carbonates with excess acid always evolves 1 mole of gaseous CO2.
On the other hand, the release of CO2 from MgCO3 will be the fastest because the sulfate formed is well soluble in water.
Title: Re: Literally no one can answer this. PLEASE EXPLAIN WHY.
Post by: Veef on January 06, 2021, 06:09:23 AM
Quote from: AWK on January 06, 2021, 02:07:05 AM
If the correct answer is d then you are giving the wrong question.
1 mole of each of these carbonates with excess acid always evolves 1 mole of gaseous CO2.
On the other hand, the release of CO2 from MgCO3 will be the fastest because the sulfate formed is well soluble in water.
https://papers.xtremepape.rs/CAIE/O%20Level/Chemistry%20(5070)/5070_s16_qp_12.pdf
question 20
Title: Re: Literally no one can answer this. PLEASE EXPLAIN WHY.
Post by: Borek on January 06, 2021, 07:19:52 AM
Quite surprising, but as AWK wrote - there is no correct answer here. All mixtures will produce the same volume of the gas.
Title: Re: Literally no one can answer this. PLEASE EXPLAIN WHY.
Post by: AWK on January 06, 2021, 08:26:14 AM
My previous comment is true.
Admittedly, the following statement can be found in chemistry textbooks for non-university schools: "The reaction of sulfuric acid with calcium carbonate proceeds only for a few moments because the salt formed, calcium sulfate, is only slightly soluble and deposits on the carbonate, preventing this compound from reacting with the acid ”, which is not real.
The reactions of barium, lead and calcium carbonates are slow, but they do.
On the other hand, the observer draws the wrong conclusions on the basis that the sediment does not disappear and no gas bubbles are visible. However, if the vessel becomes plugged and will be agitated for some time, a slight overpressure will be noticed when the vessel is unplugged. It can chemically be confirmed that it is carbon dioxide. The resulting insoluble sulfates are in no way able to form a tight layer preventing acid from allowing the carbonate surface.
The answer to the question in Cambridge IGCSE is geared to the short observation time, not the actual course of the reaction.