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Unit 1 Section 1.2 – Slide Show #2

Unit 1: Water Systems on Earth

Section 1.2: Comparing Ocean Water and Fresh Water

Slide Show #2

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1.2 Comparing Ocean Water & Fresh Water

When distinguishing between ocean water and fresh water, one should consider:

• salinity• density• freezing point

(c) McGraw Hill Ryerson 2007

3(c) McGraw Hill Ryerson 2007

1.2 Comparing Ocean Water & Fresh Water(Salinity)

• The amount of salt dissolved in a specific amount of water is called salinity.

• Ocean water’s salinity = 200X greater than fresh water

Average salinity of oceans is 35 parts per thousand

This is the same as if you mixed 35 g of salt in 1 L of water.

See page 368 - 370

from the World Ocean Atlas 2001

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1.2 Comparing Ocean Water & Fresh Water(Salinity)

• Q: Oceans at the equator and poles have the highest salinity, while oceans near rivers have low salinity. Why do you think this is the case?

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1.2 Comparing Ocean Water & Fresh Water(Salinity)

• Oceans at the equator and poles have a higher salinity since removing water increases salinity. This loss of water is caused by evaporation near the equator (high temperatures) and freezing to ice at the poles (very low temperatures).

• On the other hand, ocean locations near rivers have low salinity, due to addition of fresh water – rivers flow into the oceans.

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1.2 Comparing Ocean Water & Fresh Water(Salinity)

(c) McGraw Hill Ryerson 2007

From the diagram on the left where is salinity the highest? Lowest?

Suggest a reason for the salinity differences.

7(c) McGraw Hill Ryerson 2007

Composition of Salt Water

• Where does the salt in the water come from? Salt water is composed of

minerals dissolved in rainwater during run-offs from the land occurring over millions of years.

Volcanic eruptions also release minerals from inside Earth.

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Composition of Sea Water

(c) McGraw Hill Ryerson 2007

• Sodium ions (Na+) and chloride ions (Cl-) are the most common solids in ocean water accounting for > 75% of all solids in ocean water mixed and joined in the ocean. NaCl is chemical name for salt

• Other ions are outlined below….

9(c) McGraw Hill Ryerson 2007

Density of Salt Water

Density is the amount of mass of a substance in a certain unit volume. Density = how tightly packed the molecules are in an

object Less dense matter always floats on top more dense matter

Explain why we float better in salt water than fresh water.

What does this tell you about the density of salt water compared to fresh?

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Density of salt water continued

Question Time?????When river water meets the ocean at the river’s

mouth the water doesn’t mix together immediately. Based upon your knowledge of density describe what likely happens to the two water sources initially.

(c) McGraw Hill Ryerson 2007

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Freezing Point

• Salt water has slightly different properties than fresh water Fresh water freezes at 0 ºC Salt water freezes at –1.9 ºC

What do you think might account for the difference in freezing point?

Why would Newfoundlanders use salt on icy roads while those in Labrador use sand?

(c) McGraw Hill Ryerson 2007

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1.2 How Ocean Water Differsfrom Fresh Water (Salinity)

• Assignment 1B: p.21 - #1, 3, 5, 6, 9, 10

• Complete the Core Lab ___ on p.___.