The document contains solutions to 3 chemistry problems: 1) A 50g rock sample with 80ppm copper contains 4 mg of copper. 2) A 2g seawater sample with 850ng silicon has a silicon concentration of 1.7 ppm. 3) With the ocean's average salinity of 35 ppt and mass of 1.4x1021 kg, it contains 4.9x1020 kg of salt.

1. 1a How many milligrams of copper are there in a 50g rock
sample of 80ppm copper?
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2. 1a • Work out this proportion in grams:

3. 1a • Work out this proportion in grams:
80ppm = 80μg per g

4. 1a • Work out this proportion in grams:
80ppm = 80μg per g
• Multiply by the mass of the sample:

5. 1a • Work out this proportion in grams:
80ppm = 80μg per g
• Multiply by the mass of the sample:
80μg x 50 = 4000μg

6. 1a • Work out this proportion in grams:
80ppm = 80μg per g
• Multiply by the mass of the sample:
80μg x 50 = 4000μg
• Convert micrograms to milligrams:

7. 1a • Work out this proportion in grams:
80ppm = 80μg per g
• Multiply by the mass of the sample:
80μg x 50 = 4000μg
• Convert micrograms to milligrams:
4000
1000
= ퟒ퐦퐠

8. 1b A 2g sample of seawater contains 850ng silicon. What is
the silicon concentration in ppm?

9. 1b • Convert to μg per g to find the ppm of 1g:

10. 1b • Convert to μg per g to find the ppm of 1g:
850ng = 0.85μg

11. 1b • Convert to μg per g to find the ppm of 1g:
850ng = 0.85μg
0.85μg in 1g = 0.85ppm

12. 1b • Convert to μg per g to find the ppm of 1g:
850ng = 0.85μg
0.85μg in 1g = 0.85ppm
• Multiply by the mass of the sample:

13. 1b • Convert to μg per g to find the ppm of 1g:
850ng = 0.85μg
0.85μg in 1g = 0.85ppm
• Multiply by the mass of the sample:
0.85μg in 2g = 2 x 0.85 = ퟏ. ퟕ퐩퐩퐦

14. 1c Salinity is a unitless measurement representing grams of
salt per 1000g of seawater (i.e. ppt of salt). Considering
the ocean has an average salinity of 35, and contains
roughly 1.4 x 1021kg of water, how much salt is there in
the ocean in kg?

15. 1c • Convert this to kg of salt per kg of water:

16. 1c • Convert this to kg of salt per kg of water:
35ppt = 35mg per g = 35g per kg = 0.035kg per kg

17. 1c • Convert this to kg of salt per kg of water:
35ppt = 35mg per g = 35g per kg = 0.035kg per kg
• Multiply by the mass of the sample:

18. 1c • Convert this to kg of salt per kg of water:
35ppt = 35mg per g = 35g per kg = 0.035kg per kg
• Multiply by the mass of the sample:
0.035 x 1.4 x 1021 = ퟒ. ퟗ 퐱 ퟏퟎퟏퟗ퐤퐠