Help- Acids and Bases

[Daffodil87]

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Can some one help me with the following questions:

1.Hydrogen Cyanide forms the weak acid, hydrocyanic acid in water. Give the formula of the conjugate base of hydrocyanic acid

2. In a classroom experiment 8g of pure magnesium is dropped into an excess amount of hydrochloric acid. Calculate the volume of gaseous product formed at room temperature and pressue.

[theChemCoach]

G'day,

Two very good questions, i've competed FULL SOLUTIONS for both these questions, which are contained in the word document attached below in this post!

I have gone through EVERY single step on theory and calculations, to help you UNDERSTAND both questions, and not just be able to 'answer' them.

If you have any more questions, or need some of the concepts explained, just post in here.

Keep studying!

Regards,
George


GET THE SOLUTIONS HERE......

[Daffodil87]

Thanks for your help. A question about the magensium and colume of gas question. Since Mg has a valency of +2 and Cl a valency of -1 wouldn't the formula for magnesium chloride be MgCl2 instead of MgCl?

Also another question I have found. Lead chloride establishes an equilibrium, as shown below:
PbCl2 = Pb(2+) + 2Cl(-)
Using Le Chatelier's principle, explain what will happen to the solubility of lead chloride if the following changes were made to the mixture
(a) Hydrochloric acid is added
(b) Silver nitrate soluton is added

[theChemCoach]

Originally Posted by Daffodil87

Thanks for your help. A question about the magensium and colume of gas question. Since Mg has a valency of +2 and Cl a valency of -1 wouldn't the formula for magnesium chloride be MgCl2 instead of MgCl?

I'm sorry about that mistake, i will take more care in checking the solutions in the future.
Yes you are correct the forumla is MgCl₂
This then changes the molar ratios, which gives a different (correct) answer.
All of this has been correct in the document.

Originally Posted by Daffodil87

Also another question I have found. Lead chloride establishes an equilibrium, as shown below:
PbCl2 = Pb(2+) + 2Cl(-)
Using Le Chatelier's principle, explain what will happen to the solubility of lead chloride if the following changes were made to the mixture
(a) Hydrochloric acid is added
(b) Silver nitrate soluton is added

for (a) think of this as just adding more Cl^- ions, i.e. increasing the concentration of chloride ions.
(b) this is a little more involved, you must recognise that silver nitrate solution will dissolve up in the equilibrium, and the silver ions will react with the chloride ions and FORM A PRECIPITATE! (hence by adding silver nitrate you are effectivly decreasing the concentration of chloride ions)

Regards,
George

[Daffodil87]

Thank you very much for help

[Daffodil87]

How do you distinguish between ionisation and dissociation processes? For example:
Write equations for each and say which are ionisation and which are dissociation processes.
a) Dissolving ethanoic acid in water
b) Sulfur trioxide gas bubbled into water
c) Hydrogen iodid gas mixed with water
d) Iron III hydroxide powder stirred in water

[theChemCoach]

To put it in its simplest terms:

• dissociation: when a compound breaks down into its individual components: for example the molecule N₂(g) can dissociate into two nitrogen atoms, also HCl(g) can dissociate into its component gases.

• ionisation: this infers a change in solution (usually aqueous solutions), where by acids will ionise into the component ions.

using that distinction, try to figure out which examples correspond two which process.

goodluck,
george

[Daffodil87]

I got this question but there are no answers with it I was wondering if you could help?

Na2CO3 is ised to precipitate Pb2+ ions from the tailings of a lead mine.
Pb2+(aq) + CO3/2-(aq) = PbCO3(s)
20 000L of talings has a [Pb2+] of 1.7x 10-3mol/L
When 50kg of Na2CO3 is added the [Pb2+] drops to 5.8x10-5 mol/l
a) Calculate the number of CO3/2- ions in 50kg of Na2CO3
b) Calculate the number of moles in the lead talings
c) How many moles of lead ions remain after adding Na2CO3
d) use the results in c and d to find mass of precipitate
f) Calculate the number of moles of carbonate ions remaining in the tailings

Thanks

[theChemCoach]

Hi,

I can and probably will end up typing up a solution to this question, but will just give others to have at tackling these questions.


George