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Why Frozen Seawater Is Not Very Salty

6th grade nonfiction passage about salt in sea ice: 227 words, six questions, an answer key and vocabulary.

6th grade nonfiction salt in sea ice 227 words

Why Frozen Seawater Is Not Very Salty

If you freeze a glass of salty water, the ice that forms is less salty than the water it came from. The same thing happens in the cold polar oceans. Sea ice is made of frozen seawater, yet it holds much less salt than the sea beneath it.

The reason lies in how ice crystals grow. As water freezes, its molecules lock into a neat pattern, and salt does not fit well into that pattern. Most of the salt is pushed out and stays in the liquid water nearby. Some of it is trapped in tiny pockets of very salty water, called brine, inside the ice. Salt also lowers the temperature at which water freezes, so seawater must get a little colder than fresh water before it turns to ice.

The salt that is pushed out has a big effect. Water with extra salt is heavier, so the cold, salty water sinks below the new ice. This sinking helps to stir the ocean and carry water from the surface toward the deep.

Sea ice also changes as it grows older. Over time the pockets of brine can drain through narrow channels and drip back into the sea. Ice that has survived for years can be fresh enough that explorers have melted it for drinking water, while ice that has just formed is still too salty to drink.

Questions

  1. How does sea ice compare with the seawater beneath it? in the text

  2. What happens to most of the salt when seawater freezes? in the text

  3. What is brine in this passage? in the text

  4. Why does the water under new ice sink? in the text

  5. How does the sinking of salty water help the ocean? in the text

  6. Why is older sea ice less salty than brand new ice? think about it

Words to know

crystals
tiny solid shapes with a neat repeating pattern
molecules
the tiny pieces that make up water and other things
brine
very salty water
channels
narrow paths that liquid can flow along
polar
near the very top or bottom of the Earth
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One passage, three levels

The same topic and facts written three ways, so a mixed class can read and talk about one text. Each group’s sheet shows only a shape; the key says which is which.

● Easier · 185 words · Flesch-Kincaid grade 4

If you freeze a glass of salty water, the ice is less salty than the water. The same thing happens in the cold polar seas. Sea ice is frozen seawater, but it has much less salt than the sea under it.

Here is why. When water freezes, its tiny parts lock into a neat pattern. Salt does not fit well in that pattern. Most of the salt is pushed out and stays in the water nearby. Some is trapped in tiny pockets of very salty water, called brine, inside the ice. Salt also makes water freeze at a colder temperature than fresh water.

The salt that is pushed out is important. Salty water is heavy, so the cold, salty water sinks below the new ice. This sinking helps to stir the ocean. It moves water from the top down toward the deep.

Sea ice changes as it gets older. The pockets of brine can drain through narrow paths and drip back into the sea. Old ice can be fresh enough that explorers have melted it for drinking water. New ice is too salty to drink.

▲ This passage · 227 words · Flesch-Kincaid grade 6.4

If you freeze a glass of salty water, the ice that forms is less salty than the water it came from. The same thing happens in the cold polar oceans. Sea ice is made of frozen seawater, yet it holds much less salt than the sea beneath it.

The reason lies in how ice crystals grow. As water freezes, its molecules lock into a neat pattern, and salt does not fit well into that pattern. Most of the salt is pushed out and stays in the liquid water nearby. Some of it is trapped in tiny pockets of very salty water, called brine, inside the ice. Salt also lowers the temperature at which water freezes, so seawater must get a little colder than fresh water before it turns to ice.

The salt that is pushed out has a big effect. Water with extra salt is heavier, so the cold, salty water sinks below the new ice. This sinking helps to stir the ocean and carry water from the surface toward the deep.

Sea ice also changes as it grows older. Over time the pockets of brine can drain through narrow channels and drip back into the sea. Ice that has survived for years can be fresh enough that explorers have melted it for drinking water, while ice that has just formed is still too salty to drink.

■ Harder · 237 words · Flesch-Kincaid grade 8.9

If you freeze a glass of salty water, the ice that forms is noticeably less salty than the water it came from. The same phenomenon occurs in the frigid polar oceans. Sea ice is composed of frozen seawater, yet it contains far less salt than the sea that lies beneath it.

The explanation lies in the way ice crystals grow. As water freezes, its molecules lock together into a tidy pattern, and salt does not fit comfortably into that arrangement. Most of the salt is therefore pushed out and remains in the liquid water nearby, although some of it becomes trapped in tiny pockets of extremely salty water, called brine, inside the ice. Salt also lowers the temperature at which water freezes, so seawater must become slightly colder than fresh water before it turns to ice.

The salt that is expelled has an enormous effect. Water containing extra salt is heavier, so the cold, salty water sinks below the newly formed ice. This sinking helps to stir the ocean and carries water from the surface down toward the depths.

Sea ice also changes as it grows older. Over time, the pockets of brine can drain through narrow channels and trickle back into the sea. Ice that has survived for several years can become fresh enough that explorers have melted it for drinking water, whereas ice that has only just formed is still far too salty to drink.

Download as one PDF

How to use it

  1. Press Read it big (or B) to put the text on the projector, or Full screen (F) to fill the whole screen.
  2. Ask the questions one at a time and use Show answer when the class has decided. A shows or hides every answer.
  3. Print student copy for the class, or Print with answers for yourself.

Ideas for class

  • Before reading, put crystals, molecules, brine, channels and polar on the board with their meanings from the Words to know section and have students predict what the text will be about.
  • Read it aloud once while students follow along, then have them reread it alone or with a partner. At a calm 100 words a minute it takes about 2 minutes to read aloud.
  • Use the Read it big button (or B) to put the text on the projector, and Show answer on one question at a time so the class commits to an answer first.
  • Question 6 asks the reader to infer. Ask students to point to the words in the passage that led them to their answer.
  • Ask students to write one question the passage did not answer, then look for the answer in a book or on a classroom screen.
  • Print the student copy for independent work and keep the answer-key copy for yourself.

Related

Questions

What reading level is "Why Frozen Seawater Is Not Very Salty"?

It was written for 6th grade. It has 227 words and works out to a Flesch-Kincaid grade level of about 6.4. That is a formula's estimate from sentence length and syllables, and it is not a Lexile or a guided reading level, so check it against your students.

What do the questions ask?

There are six. 5 ask for something the text says directly and 1 ask the reader to work something out from clues. Each has an answer in the key, and the answers are written as a teacher would accept them, not as the only possible wording.

How long does it take to read?

About 2 minutes read aloud at 100 words a minute. For a one-minute fluency check, paste it into the fluency timer and use the word count.

Can I print it?

Yes. Print student copy gives the passage, the questions with lines to write on, and the word meanings. Print with answers gives the same page with the answers filled in. Both are made in your browser.

Is this passage from a published book?

No. It was written for Peabody Teach, so there is no book to buy and no login to read it.

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