VCE Chemistry Question Thread

[grannysmith]

Not necessarily, the base units can be anything really. For example, in an NMR, the chemical shift is measured in ppm, where the base unit is Hz.

Haha, my bad. I've only worked with grams and litres so please excuse my ignorance :p

[cosine]

Can someone help me with mole ratios? Why do they work
More specifically what do the coefficients in chemical reactions mean?

[Eiffel]

Just a question of the gavrimetric analysis of sulfur in fertiliser.

b) the filtrate were not tested with silver nitrate solution when the precipitate was washed in step 8.

for those who know this prac, it has something to do with the chloride ions, could someone please give me a brief with exactly what this does and why its important?

also, what is the purpose of vacuum filtration?
thanks

[chocolate.cake.1]

Hello

Does anyone know any advantages/disadvantages of volumetric analysis compared to other analytical techniques?

The only advantage I could think of is that the equipment may be relatively cheaper, but other than that I've got nothing else...

[keltingmeith]

Hello

Does anyone know any advantages/disadvantages of volumetric analysis compared to other analytical techniques?

The only advantage I could think of is that the equipment may be relatively cheaper, but other than that I've got nothing else...

Cheaper and faster is one, sure. But also, sometimes other techniques just won't tell you what you want to know easily. For example, find the concentration of a solution of HCl. Spectroscopy is useless, since you'd have to get the HCl into a metal form which is annoying, and chromatography you'd need a standard to compare to, and would have to make sure to use a solvent that HCl won't react with. A titration, however, is really easy to do, so the process is a better one.

[cosine]

How can I work out number of mole of H2O in 20.0g of CuSO4. 5H2O ? What does the '.'  mean?

[Eiffel]

can someone tell me the exact chemistry involved when heating something and its purpose?

How can I work out number of mole of H2O in 20.0g of CuSO4. 5H2O ? What does the '.'  mean?

i dont think the "." has a significant meaning, but in this case it tells us that this is hydrated coppersulfate. without the 5H20 molecules, then it is an anhydrous copper sulfate.

[cosine]

can someone tell me the exact chemistry involved when heating something and its purpose?
i dont think the "." has a significant meaning, but in this case it tells us that this is hydrated coppersulfate. without the 5H20 molecules, then it is an anhydrous copper sulfate.

Oh alright, thanks!
How can I work out number of moles on H2O? Probably the easiest question, so embarrassing

[keltingmeith]

can someone tell me the exact chemistry involved when heating something and its purpose?

Heat is a type of energy. When you heat something up, you add energy to it. This energy can then either be used to make or break bonds - you'll find out more on how putting in/taking out energy into some reagents will cause a reaction in unit 4.

[Eiffel]

Oh alright, thanks!
How can I work out number of moles on H2O? Probably the easiest question, so embarrassing

first you need to know your mass, in grams. Molar mass can be calculated by adding individual molar masses (18gmol).

moles = mass/molar mass

say it was 18 grams

then moles = 18/18 = 1 mol of H20

[Redoxify]

Oh alright, thanks!
How can I work out number of moles on H2O? Probably the easiest question, so embarrassing

You can work out the molar mass of the copper sulphate, and water, add them together, than divide the molar mass of water by the molar mass of the substance. Once you have done this you know the percentage of water in the hydrated copper sulphate. once you know the mass of water in the 20 grams you can work out the number of mole by dividing the mass by molar mass of water. I'm not a hundred percent sure

[Redoxify]

first you need to know your mass, in grams. Molar mass can be calculated by adding individual molar masses (18gmol).

moles = mass/molar mass

say it was 18 grams

then moles = 18/18 = 1 mol of H20

I think he meant the H20 in the hydrated copper sulphate, correct me if i'm wrong?

[Cogglesnatch Cuttlefish]

For the equation: NH3(aq) + H20(l) ------> NH4(+)(aq) + OH-(aq)
if asked to identify the acids and bases, are the acids H20 and NH4 and the bases NH3 and OH- or do you disregard the products?

[Redoxify]

For the equation: NH3(aq) + H20(l) ------> NH4(+)(aq) + OH-(aq)
if asked to identify the acids and bases, are the acids H20 and NH4 and the bases NH3 and OH- or do you disregard the products?

NH3 is base, H20 is acid, NH4 is the conjugate acid, and Oh- is the conjugate base

[Cogglesnatch Cuttlefish]

NH3 is base, H20 is acid, NH4 is the conjugate acid, and Oh- is the conjugate base

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