Help on a few questions (1 Viewer)

[icycloud]

Hi all,

It'd be greatly appreciated if someone could help with the following questions. Please give an explanation too! Thanks a lot. These are probably easy for you guys but I'm really behind in Chemistry...

Question One
The following reaction is allowed to establish an equilibrium

HF(aq) + H2O(l) <--> F-(aq) + H3O+(aq)

When added to this equilibrium, which of the following soluble chemicals will least affect its position?

(A) Copper (II) nitrate
(B) Hydrogen chloride
(C) Sodium hydroxide
(D) Copper (II) fluoride.

Question Two
The technique best suited to detecting low concentrations of metal ions in solutions would be:

(A) fractional distillation.
(B) gas-liquid chromotography (GLC).
(C) atomic absorption spectroscopy (AAS).
(D) nuclear magnetic resonance spectroscopy (NMR).

Question Three
While studying for an examination, a student came across the following quotes on the internet concerning anodes and cathodes.

Which of the following is the correct quote for her to learn?

(A) The anode in a galvanic cell is where oxidation occurs while an electrolytic cell has oxidation at the cathode.
(B) The anode in a galvanic cell is where reduction occurs while an electrolytic cell has reduction at the cathode.
(C) The anode in a galvanic cell is where oxidation occurs and an electrolytic cell also has oxidation at the anode.
(D) The anode in a galvanic cell is where reduction occurs and an electrolytic cell has oxidation at the anode.

What's the difference between an electrolytic and galvanic cell? Do we need to know this for the HSC?

 

[rama_v]

I think the answer to number (1) is (A) because the other compounds all produce ions which will react with the compounds in the equilibrium reaction. For example HCl produces H+ ions which reacts with water to form H₃O⁺ ions, and this forces the equilibrium to the left because there's more product beign formed. A similar argument can be applied with C and D although in the case of C, the equilibrium will be shifted to the right.

(2) The answer is (C). This is currently the very best method of detecting concentrations of metal ions (as low as part per billion).

(3) The key point to remember is that anode is where oxidation occurs, and cathode is where reduction occurs, no matter what the type of cell you are referring to. Therefore the answer is (C)

A galvanic cell is one that produces a current (i.e. it is a spontaneous reaction), but an electrolyitc cell must be supplied with current to drive a non-spontaneous reaction.

 

[sando]

I thought the anode and cathode swapped for the elctrolytic cell ????

And you almost certainly need to know the difference between a galvanic and electrolytic cell for the HSC

 

[pLuvia]

1. (A)
I think (B) will shift the eqm to the right, (C) will shift the eqm to the right and (D) will shift it to the left. But (A) will have minimal effect since the ions present in (A) won't have much effect on the eqm

2. (C), the AAS technique is based on measuring metal ions in very small concentrations, in ppm. Fractional distillation is for separating liquid mixtures which the substances in the liquid have a close boiling point. GLC is chemical principle used in analytical chemistry, mainly to separate mixtures through the different rates they travel.

3. (C) Galvanic cell is a way electricity can be generated from chemical reactions from the anode and cathode of the cell. Electrolytic cell where electrical energy is converted into chemical energy, seen in the electrolysis of water. You should have a rough idea about these two, but you should definately know the galvanic cell, if you do the module Industrial Chemistry then you would need to know the electrolytic cell as well.

 

[rama_v]

I thought the anode and cathode swapped for the elctrolytic cell ????

No. The anode is always where oxidation occurs, and the cathode is where reduction occurs. What does change, however, is whether teh anode/cathode are positive or negative...

 

[icycloud]

Wow thanks rama_v and pLuvia for the fast, prompt and insightful responses

There will be more questions to come later! I suck at Chemistry!

 

[sando]

No. The anode is always where oxidation occurs, and the cathode is where reduction occurs. What does change, however, is whether teh anode/cathode are positive or negative...

Ahh yes... now that rings a bell. These holidays are killing my memory

 

[pLuvia]

There was confusion over the anode and cathode in the physics forum once, check here