Help with some questions from CSSA 2009 (Questions provided) (1 Viewer)

[bayan92]

I did this paper at home so I need some help with a few things. :uhhuh:

• Question 19 c) Name the isotope that which undergoes beta decay to form thorium-227.
  
• Question 21
  A student weighted out a solid sample from a reagent bottle labeled NaOH. The <o></o>sample was dissolved in a volumetric flask using deionised water. This primary standard was then used in a series of titrations to determine the concentration <o></o>of a sample of vinegar. <o></o>
  
  b)<!--[endif]--> Evaluate the appropriateness of the student’s procedure. 3

THANKS!

 

[untouchablecuz]

I did this paper at home so I need some help with a few things. :uhhuh:

• Question 19 c) Name the isotope that which undergoes beta decay to form thorium-227.
  
• Question 21
  A student weighted out a solid sample from a reagent bottle labeled NaOH. The <o></o>sample was dissolved in a volumetric flask using deionised water. This primary standard was then used in a series of titrations to determine the concentration <o></o>of a sample of vinegar. <o></o>
  
  b)<!--[endif]--> Evaluate the appropriateness of the student’s procedure. 3

THANKS!

for 19. c) work backwards

we know when beta decay occurs an electron is emmited



X=277+0=277
Y=90+(-1)=89

element with atomic number of 89 is actinium

.'. the isotope is actinium-277

21. b) they have correctly weighed and dissolved a certain amount of NaOH to create a primary standard of a known quantity. in doing this, they have used de-ionised water which further increases the purity of the standard. however, one issue with the procedure is the use of NaOH. NaOH absorbs moisture from the atmosphere, altering its true molecular weight. this introduces accuracies into the the value for the concentration of the standard. generally, the students procedure is extremely appropriate, with only a technical flaw in the standard.

 

[Fortify]

for 19. c) work backwards

we know when beta decay occurs an electron is emmited



X=277+0=277
Y=90+(-1)=89

element with atomic number of 89 is actinium

.'. the isotope is actinium-277

21. b) they have correctly weighed and dissolved a certain amount of NaOH to create a primary standard of a known quantity. in doing this, they have used de-ionised water which further increases the purity of the standard. however, one issue with the procedure is the use of NaOH. NaOH absorbs moisture from the atmosphere, altering its true molecular weight. this introduces accuracies into the the value for the concentration of the standard. generally, the students procedure is extremely appropriate, with only a technical flaw in the standard.

^ That and..

NaOH is hygroscopic.

 

[untouchablecuz]

ah

so thats the word

 

[bayan92]

ah

so thats the word

What section of the syllabus is this from - like the NaOH properties?

 

[Fortify]

What section of the syllabus is this from - like the NaOH properties?

Standard Solution Dotpoint.

 

[bayan92]

Standard Solution Dotpoint.

Thanks

 

[shawty-snappin]

no, the hygroscropic thing would not be a factor, since the question says its standardised NaOH solution.

 

[Aerath]

I did this paper at home so I need some help with a few things. :uhhuh:

• Question 19 c) Name the isotope that which undergoes beta decay to form thorium-227.
  
• Question 21
  A student weighted out a solid sample from a reagent bottle labeled NaOH. The <o></o>sample was dissolved in a volumetric flask using deionised water. This primary standard was then used in a series of titrations to determine the concentration <o></o>of a sample of vinegar. <o></o>
  
  b)<!--[endif]--> Evaluate the appropriateness of the student’s procedure. 3

THANKS!

no, the hygroscropic thing would not be a factor, since the question says its standardised NaOH solution.

I can't find where it says standardised in the question....

 

[shawty-snappin]

ah ok i see, its because its a prepared solution, not pre standardised. Then yes, the rinsing and hygroscropic errors would be a major factor.

 

[arjungamer123]

for 19. c) work backwards

we know when beta decay occurs an electron is emmited



X=277+0=277
Y=90+(-1)=89

element with atomic number of 89 is actinium

.'. the isotope is actinium-277

21. b) they have correctly weighed and dissolved a certain amount of NaOH to create a primary standard of a known quantity. in doing this, they have used de-ionised water which further increases the purity of the standard. however, one issue with the procedure is the use of NaOH. NaOH absorbs moisture from the atmosphere, altering its true molecular weight. this introduces accuracies into the the value for the concentration of the standard. generally, the students procedure is extremely appropriate, with only a technical flaw in the standard.

That's wrong right there.

1) Ionic substances don't form molecules
2) You can't change the molecular weight of something unless you add new atoms or subatomic particles to it.
3) Hygroscopic is a better way to describe NaOH's deliquescent properties- and this changes the mass that you measure for dissolution in the deionised water- making the concentration of the standard solution inaccurate, and thus making your titration inaccurate. So I guess what I'm saying is that the procedure is very inappropriate. (It's drilled into us that you CANNOT use NaOH as a primary standard.)

 

[harry4]

so hygroscopic is whwre it 'absorbs', for want of a better word, water from the atmosphere

 

[Fortify]

so hygroscopic is whwre it 'absorbs', for want of a better word, water from the atmosphere

yepp . so therefore there's error in weight