EFFECT OF A SOLVENT A SOLUTE.
State and explain the observation made when Hydrogen chloride gas is dissolved in water and methylbenzene.
Solution of Hcl in water
A solution of Hydrogen chloride turns blue litmus paper red.
When magnesium or zinc carbonate is added to a solution of Hydrogen chloride in water, effervescence occurs, evidence that a gas is produced.
This is because water is a polar solution.
Polar molecule – a molecule which behaves as if it is negatively charged on one end and positively charged on the other end
A water molecule consists of one oxygen atom and two hydrogen atoms. Since the oxygen atom has a higher ability to attract the bond electrons than hydrogen, the bond pair of electrons are closer to the oxygen atom which leads to the oxygen atom developing a partial negative charge while the hydrogen atom develops a partial positive charge.
The hydrogen chloride molecule is also polar as chlorine atom has a higher ability to attract the bond electrons than hydrogen.
The chlorine end of the molecule develops a partial negative charge while the hydrogen develops a partial positive charge.
When hydrogen chloride is dissolved in water, different water molecules attract both ends of the hydrochloric molecule and cause it to dissociate. This implies that the covalent bond is broken in such a way that the pair bond electrons are left with chlorine atom, thus creating a negatively charged chloride ion and a positively charged hydrogen ion.
Hydrogen chloride solution hydrogen ions + chloride ions
Hcl (aq) H+ (aq) + Cl-(aq)
The presence of hydrogen ions in the aqueous solution of hydrogen chloride explains why it is acidic; turns blue litmus paper red and reacts with both magnesium and zinc carbonate to liberate hydrogen and carbon IV oxide gasses respectively.
Solution of Hcl in methyl benzene
On the other hand, a solution of hydrogen chloride in methyl benzene has no effect on litmus paper and does not react with either magnesium or zinc carbonate.
When hydrogen chloride gas dissolves in methylbenzene, its molecules do not dissociate and therefore no hydrogen ions are present; this explains why hydrogen chloride in methylbenzene does not exhibit acid properties.
That is; has no effect on litmus paper and does not react with neither magnesium nor zinc carbonate