HSC Chemistry Question Thread

[Piza]

Let's say that a solution of vinegar has been diluted using a 1:6 ratio.
I have found the concentration of the diluted vinegar, but I need to find the concentration of the undiluted vinegar.
Would I multiply the concentration of the diluted vinegar by 6 or by 7 (from adding the ratio numbers)?

[Piza]

You would multiply the concentration of the diluted vinegar by 6 because it is 6/1. It is the opposite of diluting which multiplies by 1/6.
Hope this helps

I understand now, thank you for your answer!!

[Kle123]

Why is it always best for First Hand Investigations to be undertaken individually?

[Aaron12038488]

i have a question regarding my prelim assessment. (Metals and Water
identify a geological, physical, biological phenomenons.

[bananna]

Hi!

What would happen if acid was added to this equation in terms of equilibrium:

CO2(g) + H2O(l)   ⇌ H2CO3(aq)

And what would happen if a base is added?

What does increase/decrease the solubility of gas mean? Which way does it mean the equilibrium is shifted?

THANK YOU!!!

[MisterNeo]

Hi!

What would happen if acid was added to this equation in terms of equilibrium:

CO2(g) + H2O(l)   ⇌ H2CO3(aq)

And what would happen if a base is added?

What does increase/decrease the solubility of gas mean? Which way does it mean the equilibrium is shifted?

THANK YOU!!!

Adding acid: The equilibrium shifts to the left.
This is because there is an increased concentration of hydrogen ions and the system will shift to the left to counter it according to LCP.
Adding base: The equilibrium shifts to the right.
This is because the base neutralises the carbonic acid, thus pushing the system to the right to replace the missing acid.

The solubility of gases refers to the ability of gases to dissolve in water. In this equilibrium, a shift to the right increases the solubility of CO2, whereas a shift to the left makes more CO2 become gaseous out of aqueous state.
Hope this helps

[Annie657]

Is BOD5 calculated by DO5 - DO0 or the other way round for water testing? Ahh  I have my assesment today 

[Jyrgal]

Is BOD5 calculated by DO5 - DO0 or the other way round for water testing? Ahh  I have my assesment today 

You should be subtracting the level of dissolved oxygen from day (1) (im assuming ur DO0 is your original measurement) to the level of dissolved oxygen at the end of 5 days (DO5), not the other way around, cause dissolved oxygen on day 1 should be higher than day 5. It's also measured in ppm with a dissolved oxygen sensor. Any BOD of 1-5ppm is considered somewhat clean, any numbers above is polluted/has bacteria. Hope this helps, goodluck for your test

[sarah96037885]

Hey y'all!  So my book only has answers not explanation. Would be a real help! if yall can explain (You don't have to give the answers if you don't want (I already have them) but if you could lead me in the right direction)
1. Complete the following equation showing the main organic products. You do not have to balance the equation but all organic compounds should be shown in structural form. If no reaction occurs, write NR.
- propan-2-ol+KMnO4 →
- pent-2-ene+HOH and H+ →
- HO(CH2)3OH+HOOC(CH2)4COOH →
2. Show by means of equations how you could convert
- propan-1-ol to propanoic acid
- but-2-yne to 2,2,3-trichlorobutane
3. How could you distinguish experimentally between an alkane, an alkene and an alkyne ?
4. How could you distinguish experimentally between primary, secondary and tertiary alcohols?
5. Arrange the following in order of increasing boiling point and use bonding theory to explain your reasoning:
CH3(CH2)4CH3
C5H11OH
C4H9COOH
CH3C(CH3)2CH2CH3
C4H10
6. Calculate the percent composition of the elements in 3-chloro-2-methylbutanoic acid.
7. 5.00 g of methanol are mixed with 20.0 g of octanoic acid and allowed to react to form an ester. If the reaction has an average yield of 75.0%, what mass of product should be formed?

[jakesilove]

Why is it always best for First Hand Investigations to be undertaken individually?

Genuinely not sure about this one; perhaps it minimises the error that different people bring? Don't think this is an important thing to understand

[jakesilove]

i have a question regarding my prelim assessment. (Metals and Water
identify a geological, physical, biological phenomenons.

Hey! This is probably too broad a question; is it a dot point? You should easily be able to identify general phenomena; Geological includes techtonic plate shifts, physical includes gravity (?) and biological includes photosynthesis.

[Jyrgal]

hello! i was just flicking over textbooks, and according to bronsted-lowry acid/base theory, a strong/weak acid has a conjugate weak/strong base. Is ammonia and ammonium an exception to this? since both of them are considered 'weak' (medium?)

If so, how would you answer a question that asks "Using bronsted-lowry acid/base theory, describe what happens when ammonia is placed into water"

[MisterNeo]

hello! i was just flicking over textbooks, and according to bronsted-lowry acid/base theory, a strong/weak acid has a conjugate weak/strong base. Is ammonia and ammonium an exception to this? since both of them are considered 'weak' (medium?)

If so, how would you answer a question that asks "Using bronsted-lowry acid/base theory, describe what happens when ammonia is placed into water"

Hi!
A conjugate base/acid of an strong acid/base is very weak.
A conjugate base/acid of a weak acid/base is weak.
The conjugate acid of ammonia (a weak base) is the ammonium ion, which is mildly strong.
The conjugate acid of a strong base like sodium hydroxide is the sodium ion, which is very weak.

Ammonia in Water

Water is amphiprotic, meaning that it can be both an acid and a base, which is why water has donated a proton to ammonia to form the ammonium ion.

[Annie657]

You should be subtracting the level of dissolved oxygen from day (1) (im assuming ur DO0 is your original measurement) to the level of dissolved oxygen at the end of 5 days (DO5), not the other way around, cause dissolved oxygen on day 1 should be higher than day 5. It's also measured in ppm with a dissolved oxygen sensor. Any BOD of 1-5ppm is considered somewhat clean, any numbers above is polluted/has bacteria. Hope this helps, goodluck for your test

Thankyou so much! Hopefully I did ok, we had to do a winkler titration 😫

[Aaron12038488]

how would i go about this question. Describe the cause and effect relationship between the appropriate properties of water to earthquakes?