VCE Chemistry Question Thread

[Redoxify]

What would you write if the question asks to identify the acids?

you would write both I believe because they are both acids so bot H2O and NH4

[Cogglesnatch Cuttlefish]

you would write both I believe because they are both acids so bot H2O and NH4

Thanks but I would like another persons input as the textbook just lists H20

[Redoxify]

Well then the question is not specific enough, because the conjugate acid should still be placed as one of the acids, unless they want you to name the reagent acid, which then yes you would only put H2O

[keltingmeith]

Thanks but I would like another persons input as the textbook just lists H20

I agree with Redoxify.

[RazzMeTazz]

I'm a bit confused with ppm

Would it be correct to say that ppm concentrations are essentially, when a substance is divided into 1 million parts and you are finding out how many of these 1 million parts is made up of another substance?

 (e.g. to find the concentration of a solute in a solution in ppm, you technically divide the solution into 1million parts and then find out how many parts of solute are present in these 1 million parts?)

So does that mean when you are considering these 1 million 'parts' the units of these 'parts' in your solution and solute would have to be the same? So you can't have 1 million parts of solution (with these parts being measured in mL) and then to find the ppm concentration of the solute in this solution, record the number of 'parts' of solute in this amount of solution in kg? (or any other unit that is not a gram)

Apologies for this really confusing question!

[grannysmith]

You can have different units. For example, ppm is commonly described as being mg/L.

Edit: to make it more clear, we assume 1mL = 1 g. Therefore 1kg = 1000g = 10⁶mg = 1000mL. Now, we say ppm = mg/L = mg/10⁶mg. See how there's a difference of 10⁶?

[RazzMeTazz]

Thanks grannysmith
yeah I understand now
!

[lzxnl]

You can have different units. For example, ppm is commonly described as being mg/L.

Edit: to make it more clear, we assume 1mL = 1 g. Therefore 1kg = 1000g = 10⁶mg = 1000mL. Now, we say ppm = mg/L = mg/10⁶mg. See how there's a difference of 10⁶?

This is only valid for water, remember.

[RazzMeTazz]

For redox reactions such as:

Zn (s) + 2HCl (aq) --> ZnCl2 (aq) + H2 (g)

When identifying what species is being reduced, is it correct to.say that:

HCl has been reduced

or

H from HCl has been reduced.
 ( Since the oxidation number of Cl remains as -1 throughout the reaction)

Thanks

[keltingmeith]

For redox reactions such as:

Zn (s) + 2HCl (aq) --> ZnCl2 (aq) + H2 (g)

When identifying what species is being reduced, is it correct to.say that:

HCl has been reduced

or

H from HCl has been reduced.
 ( Since the oxidation number of Cl remains as -1 throughout the reaction)

Thanks

Hydrogen has been reduced, BUT HCl is the oxidant.

[RazzMeTazz]

So if the question asked what has been reduced, you should answer saying: The H from HCl?

[KingDrogba]

Anyone have any good websites/documents which have practice problems containing Volumetric analysis, Redox Titrations, Back titrations, gravimetric analysis, chromatography?

Need more! Cheers

[paper-back]

Anyone have any good websites/documents which have practice problems containing Volumetric analysis, Redox Titrations, Back titrations, gravimetric analysis, chromatography?

Need more! Cheers

There are some links here: http://linkslyndale.blogspot.com.au

[KingDrogba]

There are some links here: http://linkslyndale.blogspot.com.au

What a legend!

[RazzMeTazz]

Out of gravimetric and volumetric analysis, which technique would provide more accurate results ?

Thanks