# HSC Chemistry SOLUTIONS / Thoughts / Predictions (1 Viewer)

#### 大きい男

##### Active Member

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

##### Well-Known Member
I’m not sure I know what you mean. Can you explain what ‘-log(4.3E-3)‘ means?
that means -log (4.3*10^-3)

#### Luke322

##### Well-Known Member
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

#### BlueGirl18

##### New Member
Do we need to know about biopolymers? Thanks!

#### Luke322

##### Well-Known Member
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

##### New Member

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

##### New Member
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.

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

#### NN03

##### New Member
I think it should.
View attachment 29461

The central hydrogen will see 5 neighboring hydrogens in unique environments. N + 1 rule will produce 6 peaks.
Cool thanks mate. Hope the questions tomorrow don't get too complicated with NMR.

#### Luke322

##### Well-Known Member
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

##### Active Member
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

##### Well-Known Member
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

#### Luke322

##### Well-Known Member
There might be a mistake in the question because they haven't told you the molar mass of the sample or the moles so it would be impossible to find the number of monomers

#### Rayser323

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

#### Luke322

##### Well-Known Member
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

#### Rayser323

##### New Member
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
ok thanks for the clarification!

#### Luke322

##### Well-Known Member
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.

#### hscisbotshit

##### New Member
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
im pretty sure when they got number of moles they multiplied that by avagadros constant (6.022*10^23). i have no idea why they used that constant tho