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At a high school level I suspect both would be marked correct. I've never heard of a rule for determining whether molecules hang around in multiples of the lowest common denominators - in this case P2O5. Its something you've just got to be told. http://home.clara.net/rod.beavon/oxides.htm

No, but its related to the Haber Process which is in the Syllabus.

What are stages 3 and 4 exactly? I'm only familiar with the oxidation stage and the absorption stage. Cheers

Great info, thanks. However a few hiccups The definition they give: "The term reliability refers to the consistency with which we can confirm the result (in this case the temperature change). " Only agrees with the interpretion that reliability is the spread of data or...

Possibly we are meant to interpret the BOS definition in these 2 ways. However, what happens if we decrease reliability by spreading the data out (use a "blunt" instrument) but at the same time increase the number of times we do the experiment. Have we increased the reliability? Somehow I...

Fair enough, thats one way to look at it :) However, how can someone make this interpretation and at the same time subscribe to the bull's eye model of things - where the size spread of data spread determines the reliability? If you are saying that the bull's eye model is wrong, or that...

If this is the case, then both answers A and B must be equally correct.

True. However if you take this interpretation it ignores the width of the spread itself. A large number of samples closely fitting a very wide bell-curve would rank as more reliable than a smaller number of samples done in an experiment which produced far tighter clustered results. This...

Correct, the BOS definition does not mention reliability as anything to do with how closely the data resembles a bell-curve.

The average of the sd values gets closer to 0.02 as you take more samples. Thats the converging of the estimator (sample sd) on the true population sd as sample number increases.

Sure, but the BOS definition of reliability is about the spread of the results produced by the experiment - not the results after removing the ones that suit. By the way there are no outliers which can be legitimately removed from this data, they are all within reasonable limits of...

Here's 100 results: (Sampling from normal distribution, mean =7.00, sd=0.02) sorry its so big :( pH SD <TABLE borderColor=#000000 cellSpacing=0 cellPadding=2 width=134 border=1><TBODY><TR><TD width="50%" height=16>7.04 </TD><TD width="50%" height=16> </TD></TR><TR><TD width="50%"...

Sure, but that's not reducing the spread of data (which the BOS definition calls for).

Here's data that Excel randomly generated (Tools-analysis-random number generation) from a population whose mean is 7.00 and standard deviation 0.02 - typical of a school pH measurement experiment. The right hand column tracks the standard deviation of the samples as more results are added...

Try this and see what happens to the standard deviation as you take more samples: http://www.ruf.rice.edu/~lane/stat_sim/sampling_dist/index.html

Well, thats half right. What I've actually said is that repetition may improve accuracy (if calibration etc are correct), and repetition will never improve reliability (through decreasing spread of data anyways).

If you are meaning that standard deviation should approach zero with increasing sample size (N), because N is in the denominator of: <DL><DD> </DD></DL>Well unfortunately the numerator is a variable which goes up with increasing N, so this cancels out the effect of going toward zero. I'll...

That's an interesting take on things nightshadow! However the BOS wouldn't like your definition of reliability (for first hand data) "the degree to which repeated observations and/or measurements taken under identical circumstances will yield the same results." -its only to do with spread...

As stated before, repetition does nothing to reduce the spread of data. As you take more samples the standard deviation of the samples fluctuates both up and down around a horizontal midline. If repetition decreased the spread in the data, the standard deviation amongst the samples would go...