Need help with these chemistry questions (1 Viewer)

[Dane Red]

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[Jos:)]

first question abt the indicators.

An indicator is a weak acid or weak base that will change colour in the presence of another acid and base.
The suitable eqn will be H+ + Ind- <--> HInd (all aq)
This is a suitable indicator as it has two different colours that change within a given pH range.

In this equation, when we add an acidic substance that lowers the pH, the equilibrium will shift to the right to form a red colour. When the pH is higher in the presence of a basic substance, the equilibrium will shift to the left to form more green colour. Since in an acid and base, respectively, different colours are observed, it can be used an acid-base indicator.

hope this helps.

 

[Masaken]

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second question:

ionisation involves the basic equation: HA + H2O ⇌ H3O+ + A- (reversible because citric acid is a weak acid, and *one* hydronium ion/hydrogen ion is being 'removed' for each ionisation). using this for citric acid, start with the dissociation of a citric acid molecule:

1st: C6H8O7 + H2O ⇌ H3O+ + C6H7O7- (1st ionisation - take away one hydrogen from the formula of citric acid, which becomes the hydrogen ion/hydronium ion, then minus that hydrogen so now there's 7 hydrogens in the formula left. since you've taken out a hydrogen, you need to compensate for that by putting a minus indicating that it's now become a charged ion

2nd: C6H7O7- + H2O ⇌ H3O+ + C6H6O7(2-) (2nd ionisation - same thing with above, but now the -1 charge becomes -2 because you've taken one hydrogen out, now the particle has 6 hydrogens left)

3rd: C6H6O7(2-) + H2O ⇌ H3O+ + C6H5O7(3-) (3rd ionisation - same thing with above, but now the -2 charge becomes -3 because you've taken one hydrogen out, now the particle has 5 hydrogens left)

for a strong acid, the ionisation is an irreversible one and thus has this arrow [-->]. however, if it's monoprotic, its successive ionisations will be with substances that aren't strong acids and hence their ionisations following that of the first one are reversible like the citric acid ones i showed above
(edit: made an edit because i mistakenly said that H3PO4 was a strong acid. it's weak)