No calculator on gen Chem question

[Xdentallos]

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ok so how are we supposed to do this kind of math in our head, I took a picture of how to solve a problem in the gen Chem section but the math is time consuming without calculator and at one point it divides by decimals and the answer choices weren't in formula form they were straight worked out math answers.

Can't show the picture but is the the math that were supposedly supposed to do in our head

.6 = n * (.0821) (300)

.6 = n * (24) ---> how the heck "24" mentally, all I managed to do was estimate 10% of 300 which is 30

And it gets worse

6* 10 ^-1/24= .25 * 10^-1

So I have to do 6/24 and .0821* 30 in my head under a time crunch? Do I use long division like in high school or is there a trick to use?

 

[meeshii00]

For 0.0820*300 I would first just round 0.0820 to 0.08 and then change it to 8 x10^-2. Then you can multiply (8x10^-2)(300) = 2400 x10^-2 which can be rewritten as 24. So 0.0820*30 is roughly 24. I'm not entirely sure how to do the second one.
Have you watched Chad's video? He helps a lot with figuring out shortcuts.

 

[Xdentallos]

No I haven't watch them but I need to.

That was very helpful thank you. Just ran into having to do this in my head -log 9x 10^-4 and somehow in my head I'm suppose to do a negative log calculation and get 3 as the answer... Going to look up his videos now

Just found the shortcut for doing logs in your head.

 

[meeshii00]

I definitely recommend using Chad's videos when you're studying for the DATs. He has a video where he explains how to quickly and easily solve log problems.

 

[fittycent]

I definitely recommend using Chad's videos when you're studying for the DATs. He has a video where he explains how to quickly and easily solve log problems.

For real, it blows my mind how quickly I can solve those now. After doing the quizzes (a bunch of times...) I can look at any number (e.g., 2.5 x 10^-10 or 7.2 x 10^-10) and, within five seconds, know what the [H+] or [OH-] would be -- and probably within 10 seconds know the pH or pOH. It's practically reflex at this point. Hopefully it'll help, by giving more time to work out other, less prototypical questions.

 

[Xdentallos]

For real, it blows my mind how quickly I can solve those now. After doing the quizzes (a bunch of times...) I can look at any number (e.g., 2.5 x 10^-10 or 7.2 x 10^-10) and, within five seconds, know what the [H+] or [OH-] would be -- and probably within 10 seconds know the pH or pOH. It's practically reflex at this point. Hopefully it'll help, by giving more time to work out other, less prototypical questions.

What is the legitimate website to purchase chads videos? There's coursesaver and mindsmoothie but mindsmoothie does work anymore and someone asked on his Facebook if he's still associated with coursesaver so idk where to buy them for sure

 

[Dr. Dan]

I bought them from coursesaver and it worked perfectly/its legitimate. Definitely worth every penny.

 

[embrojam]

Yup, coursesaver is legit and it hosts the videos people have been using for years. However, Chad has himself a new website, chadsvideos.com that has a new set of videos, all for free. I have used the new videos and they're great (and FREE) so check them out as well.