Using the NaCl-H2O phase diagram from Lecture 14.2, please answer the following

Question

Using the NaCl-H2O phase diagram from Lecture 14.2, please answer the following questions.

(b) The Dead Sea has a salinity of 33.7%. Assuming that this is the wt% of NaCl in water, how many phases are present in the Dead Sea and what are they? If the Atlantic Ocean is only 3.7 wt% NaCl on average, how many phases are present and what are they? Assume a temperature of 40 o F.

(c) The Titanic sank after hitting an iceberg. If the temperature was -2 o C that night, what was the salinity in the ocean in order to have the coexistence of ice and salt water?

Explanation / Answer

(b) Dead Sea: At 40 oC, at 33.7wt%, getting in a point is in the region containing boarderline of Brine and Brine+NaCl. So, 2 phase is present.

Atlantic Ocean: Getting a point at 3.7wt% at 40oC, we get only Brine. So, only 1 phase is present.

(c) At -2oC, for existance of both ice asn salt water, spotting the region, salinity will be in the range of 0-4wt%/2 = 2wt% of NaCl. Assuming 2wt%, means 2grams of NaCl in 100mL water or 2000mg NaCl in 0.1L

So, 0.1L has 2000mg

1L has NaCl = 20,000mg

So, salinity = salinity (ppt) = 0.0018066 Cl– (mg/L)

So, salinity = 0.0018066 x 20000 = 36.13

Have a nice day! :))

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