math (2 questions) logarithms and stuff

friedwontons May 17, 2018 4:11 am

ya so im stupid so im asking for help again, i think the first question is easier to understand if you took/have chemistry.
1) Siberian irises flourish when the concentration of hydrogen ions [H+] in the soil is not less than 1.58 x 10⁻⁸ mole per liter. What is the pH of the soil in which these irises will flourish?
ph=-log[H+]
okay so the answer according to the answer key i found online is 7.8013 OR LESS, i somehow managed to get that answer (probably because i was influenced by seeing the answer before solving). my concern is why is it 'OR LESS'? shouldn't it be 'OR MORE'? since the question said "not less than" which basically means more right??

2) Inequalites with logarithms: this is an example from my worksheet.
ln(4x-1)<2
ln(4x-1)<2
eˡⁿ⁽⁴ˣ⁻¹⁾<e²
0<4x-1<e²
1<4x<e²+1
¼<x<²(e²+1)
0.25<x<2.0973
on the fourth line, where did the '0<...' come from??

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Responses

ouch May 17, 2018 4:16 am

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whatthefuckwhatthefuckwhatthefuck
IS THAT THING? ew numbers and letters all combined, my worst enemy. and i actually thought chemistry was gonna be a piece of pie! may i ask what grade this is?

friedwontons May 17, 2018 4:18 am

whatthefuckwhatthefuckwhatthefuckwhatthefuckIS THAT THING? ew numbers and letters all combined, my worst enemy. and i actually thought chemistry was gonna be a piece of pie! may i ask what grade this is? ouch

chem is actually way easier for me than this, my teacher is just horrible. this is integrated math 2, aka California 10th grade (not honors)
p.s. i'm sorry if im scaring you with this HAHAHA just make sure you pay attention and dont skip class

1OvErDoSE01 May 17, 2018 4:19 am

I'm worried for the future now srry I can't be much help

KURO猫 May 17, 2018 4:19 am

ok wtf im dumb but good luck!

BananaSlayer May 17, 2018 4:27 am

1) The only answer they’re asking you is the pH so just stick with that 7,8013. Dont read answer keys before resolving the problem by it will frustrate you even more.
2) 0 is smaller or equal than 4x I should say. Honestly I’m not so sure about this

friedwontons May 17, 2018 4:33 am

1) The only answer they’re asking you is the pH so just stick with that 7,8013. Dont read answer keys before resolving the problem by it will frustrate you even more. 2) 0 is smaller or equal than 4x I should... BananaSlayer

thanks for replying, for the first one i found the pH but i don't if i should but more than 7.8013 or less than 7.8013 as the answer. i suck at word problems

BananaSlayer May 17, 2018 5:36 am

thanks for replying, for the first one i found the pH but i don't if i should but more than 7.8013 or less than 7.8013 as the answer. i suck at word problems friedwontons

Honestly I would put ph ~7,8013. That’s how usually works for me in college but idk how they evaluate you

ebjean May 17, 2018 6:33 am

I will be of no help with the 2nd ?, but for your question about why the answer for the first is that: Basically, an acid essentially gives up hydrogen. Therefore, the more acidic, ie the lower the ph, the greater the amount of hydrogen ions you'll find in the soil. Hope that explanation makes sense.

Anonymous May 17, 2018 7:05 am

1. pH is determined by the amount of "free" hydrogen ions [H+] such that the MORE [H+] something has, the LOWER the pH (as noted by your equation ph=-log[H+]). By saying "not less than", the question is actually saying, "at least or higher" so think of your final answer as saying "this soil needs this much [H+] or MORE," which translates to "this soil's pH needs to be this or LESS." Another note on significant figures since this is chem, note that the question gave this number, "1.58 x 10⁻⁸...," which comes out to 2 significant figures (2 places after the decimal point) so your final answer needs to follow the same convention meaning it should be pH</=7.80

Anonymous May 17, 2018 7:13 am

2. By law, a natural log cannot equal to a negative value (unless you include imaginary numbers, but that is a different story), hence adding the zero to the left to signify that.

friedwontons May 17, 2018 10:08 am

guys thank you so much!!! even tho my chem teacher taught acids and bases i missed three days of school that time, and then we started doing logs in math which is rly hard for me to fully grasp. again, thank you guys very much!! i have a better understanding of it now

math (2 questions) logarithms and stuff

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