HSC Chemistry Question Thread

[Mymy409]

Hey, Jake when calculating pH from the concentration of hydrogen ions, does the answer have to be to the lowest sig fig? Because in the Conquering Chemistry textbook it says that the number of sig. figs of hydrogen ions is the number of DECIMAL PLACES that should be used for pH.

[ekhan_01]

n(HCl) = c*V = 0.1*0.010 = 0.001 mol
n(HNO₃)= c*V=0.1*0.020 = 0.002 mol
n(H+ total) = 1*n(HCl) + 1*n(HNO₃) = 0.003 mol (if it were eg H₂SO₄ then you'd make it 2*n(H₂SO₄))
c(H+)=n/V = 0.003/0.030 = 0.1
pH = -log[H+] = -log(0.1) = 1
They probably made a mistake in the answers, should be A

Thank you!

Is there another way to go about the question, something to do with the limiting reagent?? < (would this be the preferred method if the ratio is NOT 1:1)

[Shadowxo]

Thank you!

Is there another way to go about the question, something to do with the limiting reagent?? < (would this be the preferred method if the ratio is NOT 1:1)

In this case it's just two acids so they don't react. You can just calculate the number of H+ ions by adding their individual amounts.
If it were an acid and a base (which it often is) you have to calculate how much reacts and what's left over. You then use what's left over to calculate the final pH.

[vanessa mbogo]

What is The typical voltage and temperature of mercury cell, membrane cell and diaphgram cell

[MisterNeo]

What is The typical voltage and temperature of mercury cell, membrane cell and diaphgram cell

Hey! I answered your question a while ago. I just moved your post to Q&A.

Hey!
From my textbook it says that:
-Mercury cell: 3-4V
-Diaphragm cell: 3.5-5V
-Membrane cell: It doesn't say but it could be the same as diaphragm cell since "membrane cell is a diaphragm cell with an improved diaphragm". But I'd ask your teacher to clarify.
It doesn't seem to mention the temperatures so I would try and use some other properties.

[Bubbly_bluey]

Hi! What are some of the sources of errors in a galvanic cell prac? Could I also use these errors with electrolytic cells as well?
Thanks

[seventeenboi]

hihi
in atmospheric ozone concentration graphs, the general trend is a decrease over the decades, however, there are also fluctuations.. what is the reason for these fluctuations?? and i also read somewhere about seasonal fluctuation or something

could someone explain this???
thanks

[MisterNeo]

Hi! What are some of the sources of errors in a galvanic cell prac? Could I also use these errors with electrolytic cells as well?
Thanks

In galvanic cell pracs, make sure that the electrodes are clean and not wet from a different prac. You would also make sure that both electrodes and the salt bridge are properly immersed in the solutions without them touching (salt bridge cannot touch electrodes coz it stops circuit).
You may be asked to calculate the E* value and account for any differences in actual and theoretical value (resistance in wires causes lower E*)
Electrolytic pracs would be similar but without the salt bridge. Concentration of the ions should be of the right amount so that the desired products are formed.
That's all I can think of

hihi
in atmospheric ozone concentration graphs, the general trend is a decrease over the decades, however, there are also fluctuations.. what is the reason for these fluctuations?? and i also read somewhere about seasonal fluctuation or something

could someone explain this???
thanks

Yeah! So the ozone concentration does decrease over time, but there are those sudden jumps in the curve. These are likely to be from protocols enacted to phase out the use of certain chemicals like CFCs, which made industries switch to HCFCs as they seemed less damaging than CFCs. However, they were also bad for ozone, hence there is a fluctuation in ozone concentration. Then came along halons and stuff, which were also bad. So the fluctuations were probably from certain bans on CFCs. I think seasonal fluctuations may have something to do with the climate, like summer has more UV rays?

[anotherworld2b]

I was wondering if anyone had any tips on how to identify which intermolecular forces are present in hydrocarbons

[MisterNeo]

I was wondering if anyone had any tips on how to identify which intermolecular forces are present in hydrocarbons

The general rule is that all carbon-hydrogen only molecules have only dispersion forces, whereas anything with -OH have hydrogen bonding and dipoles because hydroxyl groups are polar. 

[limtou]

Hello! Somehow I managed to get an answer not in the options given? Please help me out, thanks

[MisterNeo]

Hello! Somehow I managed to get an answer not in the options given? Please help me out, thanks

Did you get 29.13mL?
I think the question is incorrect since they multiplied the mass by density instead of dividing by density.
I'm guessing that their "correct answer" would have been C but that's not the case.
Which paper is this from? 

[limtou]

Did you get 29.13mL?
I think the question is incorrect since they multiplied the mass by density instead of dividing by density.
I'm guessing that their "correct answer" would have been C but that's not the case.
Which paper is this from? 

Oh yay that's what I got Was confused for a second.
It's from a recent Ruse paper

[winstondarmawan]

Hello! Does anyone have a Shipwrecks chemical equation cheat sheet they wish to share?

EDIT: Also for experimental design to test the rate of corrosion of iron and steel, would it be more valid to leave the nails in water exposed to air throughout the experiment or initially aerate the water and cap with oil? TIA

[anotherworld2b]

Oh I see now

The general rule is that all carbon-hydrogen only molecules have only dispersion forces, whereas anything with -OH have hydrogen bonding and dipoles because hydroxyl groups are polar.