Reliability of sulfate prac. (1 Viewer)

[ND]

What did you write about the reliability of that prac? I thought it said validity first, and filled up the lines, then realised it said reliability... What did you write about it? I think it would be pretty reliable, although the result would be completely wrong...

 

[crazylilmonkee]

i said it wasnt..
cos of the way the expt was carried out
and then talked bout validity haha

 

[vegeta_316]

I wrote stuff how you need good quality filter paper to make sure all of BaSO4 is caught in the filter paper cause the BaSO4 is a fine ppt and not getting all of the ppt could effect the overall calculation % composition of Sulfate in fertiliser.
I also talked about how long the filter paper with the ppt is dried. If it is not dried long enough than the BaSO4 ppt could have a greater mass then what it should, which would thus effect % composition.

 

[ND]

That's all validity, not reliability.

 

[Survivor39]

Use the electronic balance to weigh!

 

[skool_angel]

of i 4got about how BaCl is a fine ppt and it will go through the filter paper

 

[vegeta_316]

What's the difference between validity and reliability?? I looked it up in a thesaurus and reliability is a synonym for validity.

 

[underthesun]

pss, he didn't heat it and let it cool softly, since crystallisation would be slowest with largest crystals, hence easy to filter off. He didn't also add it slowly, which again, means fast crystallisation.

Additionally, he didn't filter off all the insolubles at the beginning, after putting the lawn stuff. That means, the white precipitate would not be purely precipitate, that is, it's corrupted by very evil objects. Then, this means, inaccurate.

 

[Constip8edSkunk]

meh the description was pretty dodgy cuz they gave no details what so ever, so i said depending on validity of various *undescribed* aspects of experiment, results can be reliable or unreliable, eg filtering etc, ie if its valid thn its reliable.... also said that it can b improved if more than 1 sample was tested...

but it was like a 3 sentence sketch of the procedure.... pretty hard to judge...

 

[Frigid]

i wrote something along the lines of:

the reliability of the above experiment is dependent on three factors: the number of repetitions conducted, the validity of the procedure and the available margin for error.

the chemistry of the sulfate prac is valid, because we can assume the solubility of BaSO4 is ~0%. therefore, all the ppt will be BaSO4. however, if practice, the procedure is impractical and not valid, because it is impossible to attain an accurate answer without losing ppt mass during filtration; other anions such as CO3 can corrupt the result; the final mass of ppt is dependent on the amount of drying of the sample.

since the procedure is not valid, the margin of error is great and repetitions were not conducted, the above experiment is not reliable.

once again:

 

[vegeta_316]

Well I'm sure I'll get some marks for what I wrote.

 

[ND]

Originally posted by vegeta_316
What's the difference between validity and reliability?? I looked it up in a thesaurus and reliability is a synonym for validity.

To quote spice girl:

accuracy is a measure of validity

precision is a measure of reliability

i leeched this off the prelim notes i have, but basically you have two types of errors: systematic errors and random errors..

systematic error is how far off your average reading is from the true value. it's affected by how your experiment is designed. poorly designed experiments tend to have higher systematic errors, no matter how much you repeat it.

random errors is how far off each individual reading is from the average reading (also measured in terms of standard deviation). this is usually from poor technique such as spilling, incorrect reading, etc. You usuallu repeat the experiment to minimise the effect of random errors.

accuracy is a measure of how small the systematic error is

reliability is a measure of how small the random errors are.

As you can see, reliability and validity are two different things.

 

[vegeta_316]

Man that takes some absorbing.

I can assume only a minority of people will see this difference and thus attain full marks. They are words that can be hard to tell the difference from at first glance.

 

[eeyore]

Originally posted by vegeta_316
What's the difference between validity and reliability?? I looked it up in a thesaurus and reliability is a synonym for validity.

They're different in chemistry though. Validity is stuff you can do to improve the actual prac, eg. to make sure that you're testing only the variable you're testing for.
Reliable is more like how reasonable your results are I think?

 

[braindrainedAsh]

Yeah everything I wrote about was validity... then I went shit and wrote a sentence at the end that said "The reliability of the prac could be improved by repeating it several times"

lol... pretty lame.

 

[keepin_sanity]

Reliability: is how consistant the experiment is ie. do you get the same results over and over again by following the same method?

Validity: refers to whether the method is testing what it is SUPPOSED to be testing eg. the experiment in the exam wasnt VALID because it is likely that carbonate ions were present in the lawn fertiliser which would also form precipitate with the Barium ions and the student did nothing to remove these before adding the barium. Therefore the method is not actually testing the amount of sulfate in lawn fertiliser.


Thats what my teacher says anyway...meh.
I dont care ... chemistry was my last exam!!!!!!!!!!!!!!!! YAY!!!!

 

[Frigid]

Originally posted by keepin_sanity
Reliability: is how consistant the experiment is ie. do you get the same results over and over again by following the same method?

that's all well and good, but as i said before, in the scope of the sulfate prac, there isn't much to be said of reliability:
yes, it's very reliable; reliable for repeated INACCURATE results!!!

everyone repeat with me: gravimetric analysis suxxorz.

 

[ballerinabarbie]

what about leaving the reaction for enough time for the Sulfate to fully precipitate (i remember my teacher saying something about that...)

 

[Carla2003]

I think vegeta_316 will get marks too. At least I hope so because it seems almost exact to what i wrote.
The syllabus dot point says reliability, while my teacher said to treat it as validity, so I think it must not matter too much between them.

 

[ND]

Originally posted by Frigid

that's all well and good, but as i said before, in the scope of the sulfate prac, there isn't much to be said of reliability:
yes, it's very reliable; reliable for repeated INACCURATE results!!!

Yep that's pretty much what i wrote (after all the validity crap), haha.