Terrible calculator syntax

Terrible calculator syntax

by T Boyd -
Number of replies: 2

Hi I am very frustrated trying to figure out how to work with Logs, exponents, scientific notation, and radicals. Could someone please point me to the error in this "correct answer formula" for a calculated question in Moodle quiz?

-(log(sqrt({H}e(-15))))

I'm trying to do this calculation:

pH = -log(√(Kw))

I just tried the "math equation editor" and it seems very cumbersome and awkward. And I don't think it will work with the version of Moodle my school district is using.

I also tried it with the pow(x,y) function but it didn't produce the right answers. I've almost torn out the last of my hair...

Please help!

Thanks,

  Troy

 

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In reply to T Boyd

Re: Terrible calculator syntax

by T Boyd -

The only formula I got to "work" gives me this response, which is mathematically incorrect.

-(log(sqrt(4.27E-15))) = 16.544  , I set the 4.27 as my variable {H}

Is the Moodle calculator broken? I have tried this very calculation in three different calculators, and I can't make any of them give me this answer. All the calculators I tried give the same answer: 7.185, which is correct and logical.

Hmm...

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In reply to T Boyd

Re: Terrible calculator syntax

by Pierre Pichet -

pH = -log(√(Kw))

Let's interpret this using the available info on calculated question.

Correct Answer Formula= {base}*{height} So you need the * between values (or / + -) then you want log and as you are doing some chemistry log10.

you need squareroot which is sqrt

you Kw seems to be the water constant dissociation i.e  1.0e-14  which is how to write numbers as 1,0*10-14 .

Let's suppose that it is variable ( at different temperature ) so we use variable {x}

So we get log10(sqrt({x}*1e-14))

Try it and it will give you the correct result.


If {x} = 9.7 

log10(sqrt({x}*1e-14))
 you will get 
log10(sqrt(9.7*1e-14)) = -6.5
Min: -7.1572755461536---Max: -5.8559527195801
Réponse correcte : -6.5 dans les limites de la valeur réelle -6.5066141328669

with log10(pow({x}*1e-14,-0.5))
you will get 
log10(pow(9.7*1e-14,-0.5)) = 6.51
Min: 6.4415479915381---Max: 6.5716802741956
Réponse correcte : 6.51 dans les limites de la valeur réelle 6.5066141328669
 
Pierre
 
P.S. As you I did not find it the first time I used calculated question 
 

 

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