HSC Chemistry SOLUTIONS / Thoughts / Predictions (2 Viewers)

大きい男

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Hi lads and lasses,

when rounding up pH and pOH do u recommend rounding up to sig figs or decimal places? Because for the whole year my teacher has been telling us to round it up to one decimal places, but hsc Sample solutions suggest otherwise
When you take the log of something, the number of significant figures becomes the amount of decimal places of the answer. For example, -log(4.3E-3) ≈ 2.37.
 

Luke322

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But how would that be 3 sig figs like what he said?
-log (4.3*10^-3) = 2.367 = 2.36 to 3 sig figs. It it was pH, it would be to decimal places not sig figs i.e. 3 sig figs is 13.000 for pH not 13.0
 

Luke322

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Do we need to know about biopolymers? Thanks!
Not specifically I don't think (like we don't have to know specific biopolymer's structures), but it would be good to know just a few properties just in case
 

NN03

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1,2-Dichloropropane.gif
Hey guys. Would the hydrogen atom connected to the central carbon atom have 6 splits in its proton-NMR spectrum signal? Kinda confused about line splitting.
 

Mememeist3r

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Hey guys. Would the hydrogen atom connected to the central carbon atom have 6 splits in its proton-NMR spectrum signal? Kinda confused about line splitting.
I think it should.
1604807578244.png

The central hydrogen will see 5 neighboring hydrogens in unique environments. N + 1 rule will produce 6 peaks.
 

Luke322

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Does anybody have any tips on questions asking how many isomers of a compound there are. I always get them wrong haha
 

大きい男

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Does anybody have any tips on questions asking how many isomers of a compound there are. I always get them wrong haha
I always just draw them all and think about where the functional groups can move or possible different arrangements of the carbon chain.
 

Luke322

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I always just draw them all and think about where the functional groups can move or possible different arrangements of the carbon chain.
k thanks coz I always either get one higher or one lower than the answer haha, they're so time consuming
 

Rayser323

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I figured something was missing... So the second last step to the last one, that's where you multiply by molar mass...?1604825703182.png
 

Luke322

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I figured something was missing... So the second last step to the last one, that's where you multiply by molar mass...?View attachment 29469
yeah there's a missing step there coz they just go from moles to monomers without any in-between step. The writing is pretty bad also ngl
 

Luke322

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ok thanks for the clarification!
btw for those polymer questions where they ask you to calculate the molar mass of a condensation polymer, you have to subtract n-1 number of water molar masses, where n is number of monomers not n water's, because 2 monomers join to form 1 water, so there's 1 less water.
 

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