AAS question :(

[9_7]

The mercury level in oyster is determined by dissolving 2g sample of oyster in 50mL sulfuric acid. This solution is then diluted to 400mL and a 10mL sample of the diluted solution is detected by AAS. The absorbance gave a reading of 0.45. from the calibration curve, this reading corresponded to a concerntration of 0.05ppm. Find the amount of mercury(g) in the 2g oyster sample.

Could someone please help with explanations!! thank you

[dzames]

Hey there!

Don't worry too much about the AAS part of this question, it's really just there as a topic. This questions is just asking you to figure out some concentrations and work out some dilutions.

First off, you know that your 10mL sample has a concentration of 0.05ppm. This means there is 0.05 units in 1 million units. Because of the nature of our question, we will treat units as grams and mL (they're equivalent). So we have 0.05g in 1 million mL. Awesome.

Remember that when we took this 10mL sample, we didnt change the concentration from the 400ml solution. So the 400ml solution also has a concentration of 0.05 g in 1 million mL. So how much mercury is in this 400mL? Well lets look at the mL bit. To get from 1 million mL to 400 mL, we have to divide by 2500. So lets do the same to the masses! 0.05 / 2500 gives us 2.0 x 10^-5 g. Thats how much mercury is in our 400mL solution. But remember, we only diluted one solution to reach that 400mL solution. So the mass hasn't changed! So the amount of mercury in our 2g oyster is 2.0 x 10^-5g. Sounds reasonable too - there shouldn't be too much!

[thecreeker]

just a quick question
wouldn't 2x10^-5 be multiplied by 8 to account for the dilution factor?
I didn't quite get what you mean by only diluted one solution
thanks

[barydos]

just a quick question
wouldn't 2x10^-5 be multiplied by 8 to account for the dilution factor?
I didn't quite get what you mean by only diluted one solution
thanks

The original sample was diluted just once. And dilution doesn't affect the amount of the mercury (it just means water was added). So the answer can be taken directly from the previous step.