How Ocean Water Differs from Fresh Water

Transcription

1 How Ocean Water Differs from Fresh Water Textbook pages Section 10.2 Summary Before You Read If you have ever tasted ocean water, you know that it is salty. Where did all the salt come from? Write your ideas on the lines below. Mark the Text Identify the Main Idea ocean As you read this section, stop after every paragraph and put what you read into your own words. Highlight the main idea in each paragraph. Reading Check 1. Where does the salt in ocean water come from? water 96.5% sodium 30.6% chloride 55% magnesium 3.7% sulfate 7.7% calcium 1.2% salts potassium 1.1% 3.5% others 0.7% Percentage by mass of dissolved solids in ocean water Why is ocean water salty? Most of the water that falls to the ground does not stay where it falls. Some of the water falls into streams and rivers. Some of the water flows on the surface and then joins streams and rivers. And some water seeps into the ground. Many substances dissolve easily in water. Salt is one of these substances. As water moves over the ground and rocks, it picks up salt and other substances. Sooner or later, the moving water finds its way into the ocean. When it does, the salt and other substances that were carried by the water also enter the ocean. This process has been going on for millions of years. Volcanoes on the ocean floor add salt and other substances directly into the water. Volcanoes on land send out substances high into the air. Some of this matter falls right into the ocean. Some of it falls to Earth s surface and is carried to the ocean by water as the water flows over the ground. 152 MHR How Ocean Water Differs from Fresh Water 2006 McGraw-Hill Ryerson Limited

2 Section 10.2 Summary What is salinity? The amount of salt that is dissolved in water is called salinity. Ocean water has a lot of salt in it, so ocean water has a high salinity. River water has much less salt in it than ocean water does, so river water has a much lower salinity. There are many kinds of salt that add to the salinity of the ocean. One kind is called sodium chloride. It is the same kind of salt that we add to food. About 85 percent of the salt in the ocean is sodium chloride. continued Do all parts of the ocean have the same salinity? Ocean water is saltier near the North and South Poles because when the water freezes, it leaves salt behind. Ocean water is very salty near the equator because when water evaporates it leaves the salt behind. Ocean water near continents is less salty than in the middle of the ocean because fresh water from rivers dilutes the ocean water. Does ocean water have the same density as fresh water? Density is the amount of mass in a given volume of a material. Ocean water has a higher density than fresh water because ocean water has more salt in it. If you measured the mass of 1 L of ocean water and 1 L of fresh water, what do you think you would find? For these same volumes, the mass of the ocean water would be greater than the mass of the fresh water. In other words, the density of the ocean water would be greater. Ocean water has a lower freezing point than fresh water. This means that ocean water freezes (becomes solid) at a lower temperature than fresh water does. Reading Check 2. Why is ocean water more dense than fresh water? 2006 McGraw-Hill Ryerson Limited How Ocean Water Differs from Fresh Water MHR 153

3 Ocean water Vocabulary density dissolve equator greater land less mass more North and South Poles ocean floor salinity sodium chloride volume Cloze Activity Use the terms in the vocabulary box to fill in the blanks. Use each term only once. You do not need to use all the terms. 1. Many substances, such as salt, easily in water. 2. Volcanoes on the add salt and other substances right into the water. 3. Volcanoes on send out substances high into the air. 4. The amount of salt that is dissolved in water is called. 5. Ocean water is saltier near the because when the water freezes, it leaves salt behind. 6. Ocean water is very salty near the because when water evaporates it leaves the salt behind. 7. Ocean water near continents is salty than in the middle of the ocean because fresh water from rivers dilutes the ocean water. 8. More than 85 percent of the salt in the ocean is made from. 9. The amount of mass in a given volume of a material is called. 10. Ocean water has a density than fresh water because ocean water has more salt in it. 154 MHR How Ocean Water Differs from Fresh Water 2006 McGraw-Hill Ryerson Limited

4 Comprehension Salt water Answer the questions in the spaces provided. 1. What happens to the water that falls to the ground? 2. How does the water on land add salt to the ocean? 3. How do volcanoes add salt to the oceans? 4. Why are some parts of the ocean saltier than other parts? 5. What is density? 6. Which is denser, ocean water or fresh water? 7. Which has a higher freezing point, ocean water or fresh water? 2006 McGraw-Hill Ryerson Limited How Ocean Water Differs from Fresh Water MHR 155

5 Dissolved solids Analyzing Information List the dissolved solids in water in order from the smallest percentage to the largest percentage. ocean water 96.5% sodium 30.6% chloride 55% magnesium 3.7% sulfate 7.7% salts 3.5% calcium 1.2% potassium 1.1% others 0.7% Percentage by mass of dissolved solids in ocean water 1. smallest percentage largest percentage 8. What percentage of the total mass of dissolved solids is sodium chloride? Show your work below. 9. What percentage of the total mass are dissolved solids other than sodium chloride? Show your work below. 156 MHR How Ocean Water Differs from Fresh Water 2006 McGraw-Hill Ryerson Limited

6 Assessment How ocean water differs from fresh water Term Match the Term on the left with the best Descriptor on the right. Each Descriptor may be used only once. 1. density 2. salinity Descriptor Circle the letter of the best answer. 3. Where do dissolved solids in the ocean come from? I. water on the ground II. III. A. amount of water dissolved in salt B. amount of salt dissolved in water C. amount of mass in a given volume of material D. amount of volume in a given mass of material volcanoes on the ocean floor volcanoes on land A. I and II only B. I and III only C. II and III only D. I, II, and III 4. Which of these statements is true? A. Salinity is the same everywhere in the ocean. B. Salinity is higher near the equator and the North and South Poles C. Salinity is higher near the continents. D. Salinity is higher where rivers enter the ocean. 5. How do the freezing points of ocean water and fresh water compare? A. they are the same B. ocean water has a lower freezing point C. fresh water has a lower freezing point D. ocean water does not freeze 6. How does the salinity of ocean water and fresh water compare? A. ocean water has a higher salinity B. fresh water has a higher salinity C. they are the same D. fresh water has no salinity 7. How does the density of ocean water and fresh water compare? A. ocean water has a higher density B. fresh water has a higher density C. they are the same 8. How does the mass of 1 L of ocean water and 1 L of fresh water compare? A. ocean water has a greater mass B. fresh water has a greater mass C. they are the same 9. What percentage of the salt in the ocean is sodium chloride? A. 30.6% B. 55% C. 85.6% D. 100% 2006 McGraw-Hill Ryerson Limited How Ocean Water Differs from Fresh Water MHR 157