Demonstrating Sulphuric acid is Dibasic

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Sophie Keltie

Candidate Number 2076

Centre Number 17625

Chemistry Practical Plan

Aim

The aim of my experiment is to demonstrate that sulphuric acid, H2SO4, is dibasic. Dibasic means that one mole of sulphuric acid can release two moles of hydrogen ions, H+ when it reacts in an aqueous solution. To demonstrate the dibasic nature of sulphuric acid, I shall do two experiments, one involving a titration, the other a gas collection.

Predication

In my titration, I shall neutralise an acid with a base. Firstly, I will titrate Hydrochloric Acid against Sodium Hydroxide. The balanced chemical equation for this reaction is as follows.

HCl(aq) + NaOH(aq) → NaCl(aq)  + H20(l)

Hydrochloric Acid, HCl, is a monoprotic acid, meaning that it will release one Hydrogen ion, H+ when reacted in an aqueous solution. The molar ratio in this reaction is 1:1, and therefore 1 mole of Hydrogen ions, H+, will be needed to react with 1 mole of Hydroxide ions, OH-, to form 1 mole of Water, H20. Therefore, I predict that this will mean that an equal number of moles of Hydrochloric Acid will be needed to neutralise the Sodium Hydroxide.

I shall then titrate Sulphuric Acid against Sodium Hydroxide, in comparison to Hydrochloric Acid. HCl is monoprotic, whereas H2SO4  is diprotic, and will therefore release double the amount of Hydrogen ions, H+. The reaction is as follows:

H2SO4 (aq)+2 NaOH(aq) → Na2SO4(aq)  +2H2O(l)

To demonstrate that Sulphuric Acid is dibasic, and that it will release two Hydrogen ions, H+, I predict that only half the number of moles of H2SO4  will be needed to neutralise one mole of NaOH. The molar ratio of acid to alkali is now 1:2, so for every Hydroxide ion released from the Sodium Hydroxide, two Hydrogen ions will be released from the sulphuric Acid, and so only 0.5 mole H2SO4 will be needed to neutralise 1 mole NaOH.

For the gas collection experiment, I shall again react firstly a monoprotic acid, then a diprotic acid and compare the amounts of gas collected. My first reaction will be between Hydrochloric Acid (monoprotic) with Magnesium Carbonate.

2HCl(aq) +  MgCO3(s) →  MgCl2(aq)  +  H2O(l)  +  CO2(g)  

My second reaction will be between Sulphuric Acid (diprotic), and Magnesium Carbonate.

H2SO4(aq) + MgCO3(s) → MgSO4(aq) + H2O(l)  +  CO2(g)

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For both reactions I shall collect the gas in a gas syringe, and compare the amounts of gas released. When metal reacts with acid, carbon dioxide is released. I will use acids of equal molarity, and the same mass of magnesium carbonate. I predict that the H2SO4 will produce twice the volume of gas in comparison to HCl, as this will demonstrate the dibasity of Sulphuric Acid.

Safety

Sulphuric Acid is corrosive and therefore goggles must we worn at all times. If spillages occur, these should be washed liberally with cold water. Sulphuric Acid can burn skin ...

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