Answer :
Final answer:
The scale for the concentration of 221 for PbCl₂ in water is unclear without additional context. The usual scales for concentration are ppm, ppb, ppt, and ppq, and none of these directly align with the value of 221 given the conversion from molarity to these units. (option a)
Explanation:
If the maximum concentration of PbCl₂ in water is 0.01 molarity at 298 Kelvin and its maximum concentration is 221, we must determine the scale referred to by the value of 221. When talking about concentrations, the scales usually involve parts per million (ppm), parts per billion (ppb), parts per trillion (ppt), or parts per quadrillion (ppq). Let's examine what each of these terms represents:
- 1 ppm means 1 part per 1,000,000 parts
- 1 ppb means 1 part per 1,000,000,000 parts
- 1 ppt means 1 part per 1,000,000,000,000 parts
- 1 ppq means 1 part per 1,000,000,000,000,000 parts
To express a molarity of 0.01M as a part per scale, we first need to know the weight of 1 mole of PbCl₂, which is the sum of the atomic weights of lead (207.2 g/mol) and twice that of chlorine (35.45 g/mol). This gives us:
PbCl₂ molar mass = 207.2 g/mol + 2 × 35.45 g/mol = 278.1 g/mol
Thus, a 0.01 molar solution of PbCl₂ means that there is 0.01 moles of PbCl₂, or 0.01 × 278.1 g, which is approximately 2.781 g of PbCl₂ in 1 liter of water.
To convert this to a 'parts per' scale, we take into account the density of water, which is approximately 1 g/mL or 1000 g/L. Therefore, we have 2.781 g in 1,000,000 mL of water. This corresponds to 2.781 parts in a million parts by weight, which can also be expressed as 2781 parts in a billion (ppb). Since the given concentration is 221, and it doesn't match our calculated value in ppm or ppb, it cannot represent ppm or ppb. Therefore, without further context or information, it is unclear what scale the 221 is referring to and whether it involves ppm, ppb, ppt, or ppq.
Hence, the answer is option a
