2a How many grams are there in 3 moles of H2O?

2a • Calculate how many grams are in one mole by multiplying

the number of atoms of each element by their mass:

2a • Calculate how many grams are in one mole by multiplying

the number of atoms of each element by their mass:

1 mole = 2 x 1.0079 + 1 x 15.999 = 18.015g

2a • Calculate how many grams are in one mole by multiplying

the number of atoms of each element by their mass:

1 mole = 2 x 1.0079 + 1 x 15.999 = 18.015g

• Multiply this by the number of moles in the sample:

2a • Calculate how many grams are in one mole by multiplying

the number of atoms of each element by their mass:

1 mole = 2 x 1.0079 + 1 x 15.999 = 18.015g

• Multiply this by the number of moles in the sample:

3 x 18.015 = 𝟓𝟒. 𝟎𝟒𝟒𝟒𝐠

2b Calculate the number of moles of calcium in a 1kg rock

sample, if the rock is 411 ppm calcium.

2b • Convert ppm to g per kg:

2b • Convert ppm to g per kg:

441ppm = 441μg per g

2b • Convert ppm to g per kg:

441ppm = 441μg per g

441,000μg per kg = 0.441g per kg

2b • Convert ppm to g per kg:

441ppm = 441μg per g

441,000μg per kg = 0.441g per kg

• Divide by the mass of one mole of calcium:

2b • Convert ppm to g per kg:

441ppm = 441μg per g

441,000μg per kg = 0.441g per kg

• Divide by the mass of one mole of calcium:

1 mole Ca = 40.078g

2b • Convert ppm to g per kg:

441ppm = 441μg per g

441,000μg per kg = 0.441g per kg

• Divide by the mass of one mole of calcium:

1 mole Ca = 40.078g

0.441

40.078= 𝟎. 𝟎𝟏𝟐𝐦𝐨𝐥 𝐂𝐚

2c Seawater contains around 10.8 ppt (parts per

thousand) sodium. What is this in mol/kg Na?

2c • Convert ppt to g per kg:

2c • Convert ppt to g per kg:

10.8ppt = 10.8g per kg

2c • Convert ppt to g per kg:

10.8ppt = 10.8g per kg

• Divide by the mass of sodium:

2c • Convert ppt to g per kg:

10.8ppt = 10.8g per kg

• Divide by the mass of sodium:

1 mole Na = 22.99g

2c • Convert ppt to g per kg:

10.8ppt = 10.8g per kg

• Divide by the mass of sodium:

1 mole Na = 22.99g

10.8

22.99= 𝟎. 𝟒𝟕𝐦𝐨𝐥𝐤𝐠−𝟏 𝐍𝐚

2d If all river water contained 45 ppb PO43-, and flowed

into the ocean at 3.6 x 1016 kg/year, what would be

the flux of PO43- into the ocean in mol/yr? (Hint: First

convert PO43- from ppb to molkg-1.)

2d • Convert from ppb to moles per kg:

2d • Convert from ppb to moles per kg:

45ppb = 45ng per g = 45μg per kg

2d • Convert from ppb to moles per kg:

45ppb = 45ng per g = 45μg per kg

1 mole PO43− = 30.974 + 4 15.999 = 94.97g

2d • Convert from ppb to moles per kg:

45ppb = 45ng per g = 45μg per kg

1 mole PO43− = 30.974 + 4 15.999 = 94.97g

45 x 10−6gkg−1

94.97g= 4.74 x 10−7molkg−1

2d • Convert from ppb to moles per kg:

45ppb = 45ng per g = 45μg per kg

1 mole PO43− = 30.974 + 4 15.999 = 94.97g

45 x 10−6gkg−1

94.97g= 4.74 x 10−7molkg−1

• Multiply by the flux of water:

2d • Convert from ppb to moles per kg:

45ppb = 45ng per g = 45μg per kg

1 mole PO43− = 30.974 + 4 15.999 = 94.97g

45 x 10−6gkg−1

94.97g= 4.74 x 10−7molkg−1

• Multiply by the flux of water:

4.74 x 10−7molkg−1 x 3.6 x 1016kgyr−1 = 𝟏. 𝟕𝟏 𝐱 𝟏𝟎𝟏𝟎𝐦𝐨𝐥𝐲𝐫−𝟏 𝐏𝐎𝟒𝟑−