[Slayerword]

Hi all, this is my first post. I am not expecting quick responses. This is not to copy down and hand up. I wish to understand how to solve these.

Shellfish are particularly good at concentrating heavy metals in seawater. A sample from scallops was analysed for cadmium using atomic absorption spectroscopy and the following results were obtained:

Concentration          Absorbance
0                               0.00
2                               0.10
4                               0.20
6                               0.30
8                               0.40
10                             0.50


a) Construct a Calibration Curve. (I've done this)
b) One of the scallops was removed from its shell and chopped finely in a food processor. A 2.0g portion was heated on a hotplate with 10ml nitric acid. The mixture was then analysed using AAS.

A sample of scallops gave an absorbance of 0.42. Determine:
i) The concentration of cadmium in the 10ml solution (in ppm) - (From the graph, I got around 8.2ppm)
ii) The amount of cadmium in the 10mL sample of scallop (How would i work this out? Isn't the scallop in grams?  )
iii) The amount of cadmium in the 2g sample of scallop
iv) Express the amount of cadmium (in mg) in the 2g sample of scallop as a concentration in parts per million.

Cheers, hope someone can explain this well!. Questions were adapted from a textbook...

[Borek]

2g of scallop were digested in 10 mL of nitric acid, my guess is that they really ask about amount of cadmium in this solution (which will be identical to the amount in 2g of tissue). If that's what they are looking for, wording is lousy and can be confusing.

[Slayerword]

2g of scallop were digested in 10 mL of nitric acid, my guess is that they really ask about amount of cadmium in this solution (which will be identical to the amount in 2g of tissue). If that's what they are looking for, wording is lousy and can be confusing.

I was thinking about that... but doesn't nitric acid produce cadmium too? I'm confused, I'll ask some of my peers. Cheers for your input though.

[Borek]

Nitric acid doesn't "produce" cadmium. It cab be contaminated with cadmium, but it probably isn't - or at least you are not told it is, so you don't have to worry about it.