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October 28, 2025, 02:50:01 pm
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Author Topic: Random Question Thread.  (Read 13202 times)  Share 

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d0minicz

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Random Question Thread.
« on: March 25, 2009, 08:51:24 pm »
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Hi if i have 18.5ppm and i want to convert it to mg/g would it be 18.5mg /kg --> 0.0185mg / g ?
also for the question the manufacturer's claim is "not more than 200mg/g" for that substance
just need verification because it seems a bit weird
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TrueTears

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Re: Random Question Thread.
« Reply #1 on: March 25, 2009, 08:57:16 pm »
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Quote from: d0minicz on March 25, 2009, 08:51:24 pm
Hi if i have 18.5ppm and i want to convert it to mg/g would it be 18.5mg /kg --> 0.0185mg / g ?
also for the question the manufacturer's claim is "not more than 200mg/g" for that substance
just need verification because it seems a bit weird
Yes 18.5 ppm = 0.0185 mg/g
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d0minicz

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Re: Random Question Thread.
« Reply #2 on: March 25, 2009, 10:21:50 pm »
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Hey I'm a bit confused with complementary colours.
So if a solution is blue, we use orange light to analyse right?
Can someone explain why, in terms of how the solutions gets this colour , ie. whats transmitted etc? I have a fair idea just need to verify in detail . . .

thank you =]
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TrueTears

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Re: Random Question Thread.
« Reply #3 on: March 25, 2009, 10:26:19 pm »
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Yes that's right, UV-Visible spectroscopy is all about complementary colours.

So we perceive something to be blue because it ABSORBS orange light (the complement of blue), since that solutions absorbs all the orange, blue is the only colour which reaches our eyes.
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d0minicz

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Re: Random Question Thread.
« Reply #4 on: March 26, 2009, 05:37:35 pm »
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A 1.000g sample was dissolved in 1000mL. A 20mL sample of this was taken. Concentration of phosphorous in this sample is 13ppm.
How would i go about finding the percentage by mass of phosphorous in the sample?

thanks.
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TrueTears

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Re: Random Question Thread.
« Reply #5 on: March 26, 2009, 05:47:57 pm »
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so that means in 20 mL ( ) sample there will be mg of Phosphorous.

now mol of Phosphorous in 20 mL

Now concentration of P =

Now in 1000mL the concentration is the same so mol of P in 1000 mL

so g

so % of P = %

« Last Edit: March 26, 2009, 05:50:56 pm by TrueTears »
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hard

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Re: Random Question Thread.
« Reply #6 on: March 26, 2009, 06:24:25 pm »
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we're already doing chemistry revision for mid yr exams and all ive learnt his yr for chem was the word stoichiometry.
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jackinthepatch

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Re: Random Question Thread.
« Reply #7 on: March 26, 2009, 06:28:36 pm »
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Yeah I'm fucked
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d0minicz

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Re: Random Question Thread.
« Reply #8 on: March 26, 2009, 06:31:40 pm »
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Same .
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d0minicz

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Re: Random Question Thread.
« Reply #9 on: March 26, 2009, 06:43:48 pm »
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If a sample containing magnesium was dissolved in 100mL, and found to have 5mg/L of magnesium, how would i find the mass of magnesium in grams?
thnkz
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jackinthepatch

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Re: Random Question Thread.
« Reply #10 on: March 26, 2009, 06:49:28 pm »
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If there are 5mg in 1L then in .1L you will have 5mg divided by 10.

This means you will have 0.5mg in 100mL. Multiply this by 100 and you get it in grams: 0.0005g.
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Over9000

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Re: Random Question Thread.
« Reply #11 on: March 26, 2009, 06:52:11 pm »
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Chem is alrite some topics are good (like organic chemistry) but wtf is up with chromotography, I slept through every lesson, I honestly dont know one thing about it
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IntoTheNewWorld

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Re: Random Question Thread.
« Reply #12 on: March 26, 2009, 06:52:34 pm »
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Here's how I would usually do these sorts of questions

Sample of magnesium : 100ml
                   0.005g : 1000ml (just converted concentration given into more suitable units)

Therefore sample of magnesium using (cross multiplication) 0.005g * 100ml / 1000ml = 0.0005g
« Last Edit: March 26, 2009, 07:31:15 pm by SmRandmAzn »
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jackinthepatch

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Re: Random Question Thread.
« Reply #13 on: March 26, 2009, 07:10:03 pm »
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Quote from: Over9000 on March 26, 2009, 06:52:11 pm
Chem is alrite some topics are good (like organic chemistry) but wtf is up with chromotography, I slept through every lesson, I honestly dont know one thing about it

Chromatography and spectroscopy can suck a fat one
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hard

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Re: Random Question Thread.
« Reply #14 on: March 26, 2009, 07:55:46 pm »
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Quote from: Over9000 on March 26, 2009, 06:52:11 pm
Chem is alrite some topics are good (like organic chemistry) but wtf is up with chromotography, I slept through every lesson, I honestly dont know one thing about it
that's what i was gonna say but i couldn't bee effd. +1

edit: what's worse is my teacher says it so badly.
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