Post your chemistry questions here. (2 Viewers)

Alkanes

Active Member
Joined
May 20, 2010
Messages
1,417
Gender
Male
HSC
2012
Ca + 2H2O -----> H2 + Ca(OH)2

n = 0.1 L x 3.16 x 10^-2
= 0.00316 moles

V(H2) = 0.00158 mol x 24.79 L/mol
= 0.0389 L

I think its right.
 
Joined
Apr 5, 2011
Messages
165
Location
I'm right here guys
Gender
Female
HSC
2011
Q: A 5g tablet contains sodium carbonate. The tablet was crushed then reacted with 20mL, 0.1M HCl. The excess acid was titrated against 0.1M NaOH needing 5mL. Calculate % of sodium carbonate in the tablet

Free rep whoever comes with correct answer!
 

RANK 1

Active Member
Joined
Mar 16, 2011
Messages
1,369
Location
the hyperplane
Gender
Male
HSC
2011
Q: A 5g tablet contains sodium carbonate. The tablet was crushed then reacted with 20mL, 0.1M HCl. The excess acid was titrated against 0.1M NaOH needing 5mL. Calculate % of sodium carbonate in the tablet

Free rep whoever comes with correct answer!
1.58985%

2% (1 s.f)
 

snorelacks

Member
Joined
Aug 6, 2011
Messages
53
Gender
Female
HSC
2011
Still a bit confused with titration questions.
25.0mL of 0.12M standard barium hydroxide solution was titrated with nitric acid. The results are recorded as below
Titration 1 : 20.4mL
Titration 2 : 18.1mL
Titration 3 : 18.2mL
Titration 4 : 18.1mL

Calculate the concentration of nitric acid.
I basically understand the whole question, but still am confused as to when I have to add the two volumes of known solutions together? (for the last step to find the concentration)
 

RANK 1

Active Member
Joined
Mar 16, 2011
Messages
1,369
Location
the hyperplane
Gender
Male
HSC
2011
Still a bit confused with titration questions.
25.0mL of 0.12M standard barium hydroxide solution was titrated with nitric acid. The results are recorded as below
Titration 1 : 20.4mL
Titration 2 : 18.1mL
Titration 3 : 18.2mL
Titration 4 : 18.1mL

Calculate the concentration of nitric acid.
I basically understand the whole question, but still am confused as to when I have to add the two volumes of known solutions together? (for the last step to find the concentration)
excluding the rough titre, the average is 0.018333...L

Ba(OH)2 + 2HNO3 ---> 2H2O + Ba(OH)2

therefore CBa(OH)2VBa(OH)2=1/2CHNO3VHNO3 as the stoichiometry is 1:2

[0.12][O.O25] = [1/2]C[0.018333..]
[1/2]C = [0.12][0.025]/[0.018333..]
[1/2]C = 0.165441176
C = 0.330882352 mol/L
C = 0.331 mol/L (3 s.f)
 

RANK 1

Active Member
Joined
Mar 16, 2011
Messages
1,369
Location
the hyperplane
Gender
Male
HSC
2011
I think this one you need to disregard the first titration and take the average of the last 3. So firstly find the number of moles which you should get 0.003 moles.

C = 0.003 mol / [(18.1+18.2+18.1)/3/1000)]
= 5.4 x 10^5 mol/L

I think
its definitely not 5.4 x 10^5 mol/L
 

Alkanes

Active Member
Joined
May 20, 2010
Messages
1,417
Gender
Male
HSC
2012
Ahh shit silly me.. Forgot to write an equation hence why the mole ratios fked up.. =(

So it would be C = 0.006 / 0.018333
= 0.330882 mol/L
= 0.33 mol/L (2sf)

Also wouldn't it be 2 sf not 3?
 
Last edited:

Alkanes

Active Member
Joined
May 20, 2010
Messages
1,417
Gender
Male
HSC
2012
Don't you take into account from 0.12 M ?
 

apollo1

Banned
Joined
Sep 19, 2011
Messages
938
Gender
Male
HSC
2011
can someone explain to me the stupid significant figures thing in chemistry. pisses me off.

Also heres a question:

Screen shot 2011-10-07 at 4.46.16 PM.jpg

explanation plz with answer. :)
 

Alkanes

Active Member
Joined
May 20, 2010
Messages
1,417
Gender
Male
HSC
2012
can someone explain to me the stupid significant figures thing in chemistry. pisses me off.

Also heres a question:

View attachment 23145

explanation plz with answer. :)

Your final answer should only posses the lowest sig figs from the data. So for example you're given 0.1555 g (4sf) of magnesium and oxygen 15.1g 3 (sf). Find the mass of magnesium oxide. You answer should be only 3 sf. xx.x g or 0.xxx g
 
Last edited:

umz93

Member
Joined
Mar 4, 2010
Messages
350
Gender
Male
HSC
2011
Can someone please explain oxidation/reduction states to me.
 

Reikira

Member
Joined
Mar 8, 2010
Messages
68
Gender
Male
HSC
2012
Q: Using TWO examples, analyse how the features of catchment areas will determine the water treatment necessary to make the water safe to drink.
 

RANK 1

Active Member
Joined
Mar 16, 2011
Messages
1,369
Location
the hyperplane
Gender
Male
HSC
2011
Q: Using TWO examples, analyse how the features of catchment areas will determine the water treatment necessary to make the water safe to drink.
i did this question yesterday, ill answer it after diiner
 

RANK 1

Active Member
Joined
Mar 16, 2011
Messages
1,369
Location
the hyperplane
Gender
Male
HSC
2011
Can someone please explain oxidation/reduction states to me.
oxidation/reduction states refers to the charge an atom has or the number of extra or reduced electrons an atom has on the outer valence shell.
 

RANK 1

Active Member
Joined
Mar 16, 2011
Messages
1,369
Location
the hyperplane
Gender
Male
HSC
2011
Q: Using TWO examples, analyse how the features of catchment areas will determine the water treatment necessary to make the water safe to drink.
'Features of catchment areas that determine if water treatment is necessary include proximity to farmland, sewage and mines. Farmlands and sewage areas release effluents into the water, causing the water to have to be treated before consuming. Bacteria, such as E.coli from feces also need to be treated before the water is safe to consume, chlorination would be a suitable treatment. Screening and filtering may also be necessary to remove particles from sewage run offs.

mines are a potential source of harmful heavy metals which could leak into the waterways. an example of a harmful heavy metal is lead, which is bioaccumulative, affects enzyme production, hemoglobin production in humans and can kill if the body absorbs too much lead. water near mines would need to be treated with ion selective membranes such as PTFE.'
 

Users Who Are Viewing This Thread (Users: 0, Guests: 2)

Top