VCE Chemistry Question Thread

[f0od]

would anyone be able to help me out with some volumetric analysis questions please?

1. During a practical class, the ammonia content of a window cleaning solution was determined using volumetric analysis. 20mL of cleaner was pipetted into a volumetric flask and the volume made up to 250mL  using distilled water. A 25mL aliquot of this diluted cleaner solution required 24.35mL of 0.187M hydrochloric acid for neutralisation. Methyl orange was used to indicate the endpoint. Calculate the concentration (in mol L-1) of ammonia in the window cleaner.

2. Nitric acid may be used for etching designs on copper objects. A commercially available nitric acid has a concentration of 15M. What volume of this concentrated acid is needed to prepare 500mL of a 2.5M solution used in copper etching?

Thank you in advance!

[Yertle the Turtle]

would anyone be able to help me out with some volumetric analysis questions please?

1. During a practical class, the ammonia content of a window cleaning solution was determined using volumetric analysis. 20mL of cleaner was pipetted into a volumetric flask and the volume made up to 250mL  using distilled water. A 25mL aliquot of this diluted cleaner solution required 24.35mL of 0.187M hydrochloric acid for neutralisation. Methyl orange was used to indicate the endpoint. Calculate the concentration (in mol L-1) of ammonia in the window cleaner.

2. Nitric acid may be used for etching designs on copper objects. A commercially available nitric acid has a concentration of 15M. What volume of this concentrated acid is needed to prepare 500mL of a 2.5M solution used in copper etching?

Thank you in advance!

1. First you would find the number of moles of HCl that neutralised the solution using n=cV, and then write out the neutralisation reaction to find the mole ratio between HCl and NH₃, which helps you find the number of moles of NH₃ in the diluted solution. Then find the concentration and use the formula c1V1=c2V2 to find the initial concentration in the window cleaner, where V1=20mL and V2=250mL.

2. You would again use the formula c1V1=c2V2 where c1=15, c2=2.5, V1=? and V2=0.5.

Hope this helps!

[f0od]

1. First you would find the number of moles of HCl that neutralised the solution using n=cV, and then write out the neutralisation reaction to find the mole ratio between HCl and NH₃, which helps you find the number of moles of NH₃ in the diluted solution. Then find the concentration and use the formula c1V1=c2V2 to find the initial concentration in the window cleaner, where V1=20mL and V2=250mL.

2. You would again use the formula c1V1=c2V2 where c1=15, c2=2.5, V1=? and V2=0.5.

Hope this helps!

thank you heaps! i got the same numerical figures, but i was a decimal point off in both answers? i'm not sure if i did some working wrong, or if the answers are wrong (because they are handwritten, so the teacher may have messed it up? but i think i got them wrong aha)

for 1. i got 0.228M while the answer is 2.28M and for 2. i got 0.083L while the answer is 0.83L

is there any chance you would be able to confirm these for me? else i will ask my teacher when we get back to school! sorry for bothering you, but thank you so much again!

[Yertle the Turtle]

thank you heaps! i got the same numerical figures, but i was a decimal point off in both answers? i'm not sure if i did some working wrong, or if the answers are wrong (because they are handwritten, so the teacher may have messed it up? but i think i got them wrong aha)

for 1. i got 0.228M while the answer is 2.28M and for 2. i got 0.083L while the answer is 0.83L

is there any chance you would be able to confirm these for me? else i will ask my teacher when we get back to school! sorry for bothering you, but thank you so much again!

I found both of the proper answers to be correct. My guess is that you forgot to translate all the volumes from mL into L. If not, send me a PM and I'll send you my full working out.

[lorennnz]

How do you name amines?

My teacher taught us that VCAA prefers using the IUPAC system and that we should use amino- prefix. But I told her IUPAC uses an -amine suffix (at least that's what the textbook said) but she keeps on saying we have to use amino-. Help please! Thank you

[Yertle the Turtle]

How do you name amines?

My teacher taught us that VCAA prefers using the IUPAC system and that we should use amino- prefix. But I told her IUPAC uses an -amine suffix (at least that's what the textbook said) but she keeps on saying we have to use amino-. Help please! Thank you

You are correct, in the IUPAC nomenclature system, the amine group is a suffix, such as butan-1-amine. Do not use amino- prefix. There is a naming priority table in the Heinemann textbook that shows which functional group is most important, refer to this when naming molecules.

[Bri MT]

How do you name amines?

My teacher taught us that VCAA prefers using the IUPAC system and that we should use amino- prefix. But I told her IUPAC uses an -amine suffix (at least that's what the textbook said) but she keeps on saying we have to use amino-. Help please! Thank you

The amino prefix can be used if the molecule has a higher priority fictional group (as the high priority one will be designated in the suffix) .

[Azim.m]

Why is biodiesel more viscous than diesel?
Is it to do with the fact that methyl esters are a longer carbon chain than diesel and the presence of the ester bond that allows for the formation of dipole dipole attractions?

[neenah]

Hey can anyone help me with this question? I don't understand how to do it or how they got the answer? Thanks!

"2HI(g)   H2(g) + I2(g)
An equilibrium mixture in a 2.0 L vessel at this temperature contains
0.220 mol of H2 and 0.110 mol of I2.
c. A third mixture consisted of 1.0 mol of HI, 0.24 mol of H2 and 0.32 molof I2 in a 2.0 L container at 330°C. Decide if the mixture is at equilibrium and, if not, predict the direction the reaction will shift to reach equilibrium."

[Lear]

Are question on polymers and polymerisation still relevant and able to be assessed?

[lazaward]

When doing earlier exams off vcaa, what is no longer in the study design? Especially the change from 2016 study design to the current study design

[Guideme]

is the Kinetic Molecular Theory part of the study design and  will it be tested in the exam?

Just curious since it wasnt in my SAC
Thank You

[passbleh24]

I just have a question about rounding and significant figures.
I went through the 2010 Chem Exam 1 and 1e is really confusing me.
I have attached VCAA's working out.

1. I got 3.81*% is this more or less correct than the 3.82% without the " * " ? I do not understand why there are 2 answers.
2. My full was 3.812% which is to 4 significant figures where as VCAA's answer has it to 3 significant figures. I based this on the 80.50g of sample that was used.

Thank you any input!!

[Mattjbr2]

I just have a question about rounding and significant figures.
I went through the 2010 Chem Exam 1 and 1e is really confusing me.
I have attached VCAA's working out.

1. I got 3.81*% is this more or less correct than the 3.82% without the " * " ? I do not understand why there are 2 answers.
2. My full was 3.812% which is to 4 significant figures where as VCAA's answer has it to 3 significant figures. I based this on the 80.50g of sample that was used.

Thank you any input!!

Iron is given to 3 sig.fig. in the data book. Therefore your answer should be 3 sig.fig. The answer is 3.81% if you use 3.07g or 3.82% if you use 3.0745g. I prefer 3.07 and 3.81% because of the accuracy thing. I'm leaning towards them accepting either, and I think that's what they meant when they bolded both numbers.

[passbleh24]

Iron is given to 3 sig.fig. in the data book. Therefore your answer should be 3 sig.fig. The answer is 3.81% if you use 3.07g or 3.82% if you use 3.0745g. I prefer 3.07 and 3.81% because of the accuracy thing. I'm leaning towards them accepting either, and I think that's what they meant when they bolded both numbers.

Thank you soo much, that makes a lot more sense.