sci-fi's chem qst.s

[Mao]

understanding hazards, dangers and environmental impacts are a small part of both unit 3 and 4

but with that said, it's only a small part. if you pay attention to safety in pracs, and understand the very basics of acid rain (when you eventually learn about sulfuric acid), you don't need to spend much more effort on top of that.

[sci-fi]

Find the [H+] given that [OH-]=2.8 x 10-5

not sure of the [H+] in this qst. (is it 3.57 x 10-10M)




cheers.

[Mao]

[H⁺]*[OH^-]=10^-14 M²

[sci-fi]

6) A swimming pool has a volume of one million litres. How many grams of HCl would need to be added to that swimming pool to bring the pH down from 7 to 4? (assume the volume of the HCl is negligible)

edit:

5) Find the pH and pOH of a solution with a volume of 5.4L that contains 15grams of HCl and 25grams of HNO3 (nitric acid)?

[Collin Li]

Find the [H+] given that [OH-]=2.8 x 10-5

not sure of the [H+] in this qst. (is it 3.57 x 10-10M)

Yes, you're right, although you should have 2 significant figures.

6) A swimming pool has a volume of one million litres. How many grams of HCl would need to be added to that swimming pool to bring the pH down from 7 to 4? (assume the volume of the HCl is negligible)

[sci-fi]

thanks coblin,  champ.

[Collin Li]

5) Find the pH and pOH of a solution with a volume of 5.4L that contains 15grams of HCl and 25grams of HNO3 (nitric acid)?

Steps

1. Calculate the total amount of present by calculating the amount of and , and adding up all the protons released by them.



2. Now find the concentration of (divide by 5.4 L), and hence find the concentration of

Use these rules:

[sci-fi]

cheers, i dont understand pOH because its not in our textbook.

what exactly is pOH?

edit: power of hydroxide?

[Collin Li]

You just need to use these formulas:











The pOH is the exact same mathematical function, except applied to the concentration of hydroxide ions, rather than protons. I guess you could call it that (power of hydroxide).

Just try to use a bit of commonsense (don't be afraid to guess), when you're faced with some unknowns that look similar. One day, if you do Chemistry in first year university, you'll see . No rewards for guessing the formula for that!

[sci-fi]

ok. thanks coblin.

edit: just removed some questions because i understand the pOH now. :police: (fuuny emoticon; so i'll jst use it)  :police: :police: :police:

[sci-fi]

I understand that Chemistry Units 1/2 are the foundations to 3/4.. (derr..anyone can figure that out) but are the topics/area of studies in Chemistry 1/2 examinable in the 3/4 exams? Because for methods and spesh (i think), the units 1/2 or gen. math adv. are included in the 3/4's.


edit: for example. will i have to memorise and revise the entire book of units 1/2,,, the history. periodic arrangment of the subshells etc etc

[Collin Li]

Hmm... Don't worry about the history, but you should try to know the subshell arrangements (but honestly, you don't really need to know it for Units 3&4, but it pains me to tell someone not to bother with the more fundamental details of Chemistry).

You will find a lot of stoichiometry in Units 3&4. Understand redox and acid-base processes well.

[sci-fi]

thanks mate!! (yay no history)& subshell config