Phosphorus is present in seawater to the extent of 0.07 ppm by mass. Assuming that the phosphorus is present as dihydrogenphosphate, H2PO4-, calculate the correspond-ing molar concentration of H2PO4- in seawater.

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Understand that 0.07 ppm (parts per million) means 0.07 grams of phosphorus per 1,000,000 grams of seawater.

Calculate the mass of phosphorus in 1 liter of seawater, assuming the density of seawater is approximately 1 g/mL, which means 1 liter of seawater weighs about 1000 grams.

Determine the mass of phosphorus in 1 liter of seawater using the ppm value: (0.07 grams of phosphorus / 1,000,000 grams of seawater) * 1000 grams of seawater.

Convert the mass of phosphorus to moles using the molar mass of phosphorus (approximately 30.97 g/mol).

Assume all phosphorus is present as dihydrogen phosphate (H2PO4-), and use the moles of phosphorus to find the molar concentration of H2PO4- in seawater.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Parts Per Million (ppm)

Parts per million (ppm) is a unit of measurement used to describe the concentration of a substance in a solution. It indicates how many parts of a substance are present in one million parts of the total solution. In this context, 0.07 ppm means that there are 0.07 grams of phosphorus per one million grams of seawater, which is essential for calculating molar concentration.

Molar Concentration

Molar concentration, or molarity, is defined as the number of moles of solute per liter of solution. It is a crucial concept in chemistry for quantifying the concentration of a substance in a solution. To find the molar concentration of H2PO4- in seawater, one must convert the mass of phosphorus from ppm to moles and then relate it to the volume of seawater.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). For dihydrogen phosphate (H2PO4-), the molar mass is calculated by summing the atomic masses of its constituent elements: hydrogen, phosphorus, and oxygen. This value is essential for converting grams of phosphorus to moles, which is necessary for determining the molar concentration in seawater.

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