Water Cycle & Evaporation - Hilary Sci 2.2, PDF

## Water Cycle ### 2.2 Water Cycle #### Flipped Classroom * Watch a video and answer the questions. #### A Processes of the Water Cycle * In Nature, water keeps changing between liquid water and water vapor. * Water goes round and round between the land, the sky and the sea. * The way water circu...

## Water Cycle ### 2.2 Water Cycle #### Flipped Classroom * Watch a video and answer the questions. #### A Processes of the Water Cycle * In Nature, water keeps changing between liquid water and water vapor. * Water goes round and round between the land, the sky and the sea. * The way water circulates in Nature is called the water cycle. * The figure below shows the main processes in the water cycle. #### Diagram: The Water Cycle * **Sun** * **Clouds (fresh water)** - The water droplets join together to form clouds. * **Water vapor** - Evaporation occurs when sunlight warms the surface of the water. * **Sea (salty water)** * **Condensation:** As the upper part of the sky is cooler, the water vapor cools down and condenses to form small water droplets. * **Evaporation:** Energy from the sun drives the water cycle. * **Precipitation:** Precipitation forms in the clouds when water vapor condenses and forms bigger and bigger water droplets. When the droplets are heavy enough, they fall as rain. * **Transportation:** Clouds may be carried to other places by wind. * **Rain (fresh water)** * **Snow (fresh Water** * **River (fresh water)** * **Lake (fresh water)** **Big Science Ideas** * **Change and constancy in the water cycle** * In the water cycle, water keeps changing between liquid water and water vapor. However, the total amount of water on Earth remains constant. ### 2.2 Practical: How Rain is Formed #### Aim * To simulate* the formation of rain. #### Apparatus and Material per Group * Large beaker (400 cm³) * Small beaker (100 cm³) * Clear plastic bag * Metal dish * Tongs * Towel * Preheated pebbles * Hot water * Red ink * Crushed ice * Dish soap #### Procedure 1. Apply a thin layer of dish soap on the upper, inner wall of a large beaker. This can prevent the formation of mist on the inner wall. 2. Gently put some preheated pebbles into the large beaker with a pair of tongs. 3. Add hot water to the large beaker until it just covers the pebbles. Add several drops of ink to the water. 4. Put a small beaker inside the large beaker to collect the ‘rain’ formed. 5. Put a bag of ice on a metal dish. Cover the large beaker with the dish. #### Observation * **What do you observe on the bottom of the metal dish?** - Liquid droplets are formed on the bottom of the metal dish. They join together and fall like rain. * **What color is the ‘rain’** - It is colorless. #### Discussion * **Which parts in the water cycle do the following parts in the set-up represent?** * **Water in the large beaker:** *Water in the sea, rivers and on land* * **Preheated pebbles:** *The Sun* * **Cold metal dish:** *The upper part of the sky* * **Explain how ‘rain’ is formed in the beaker.** - Water _____*evaporates*_____ to form water vapor. The vapor rises upwards. - When the vapor meets the cold metal dish, it cools down and _____*condenses*_____ to become water. When the drops of water are too heavy, they fall as ‘rain’. #### Big Science Ideas * **Model of the water cycle:** Scientists sometimes* use models to help explain, predict and study how real objects work. A model is a representation of a real system, object, or concept. For example, the set-up in Practical 2.2 is a model to help explain the water cycle. However, it has limitations. For example, it cannot simulate the sun as a source of energy. Besides, it cannot show clouds being carried to other places by the wind. ### 2.2 Key Point * The water cycle involves the following processes: * Evaporation * Condensation * Precipitation * Transportation ### 2.2 Quick Check * **Write ‘T’ for a true statement and ‘F’ for a false statement in the boxes provided.** * 1. Boiling is not involved in the water cycle. **F** * 2. Clouds are made up of water vapor. **T** ### B Rate of Evaporation * When we hang wet clothes for drying, we often unfold the clothes to make them dry more quickly. Why do wet clothes dry more quickly when they are unfolded? This is because the *rate of evaporation* of water is higher when the surface area exposed to air is larger. **Fig 2.13** Wet clothes dry more quickly when they are unfolded. * Besides the surface area exposed to air, what other factors affect the rate of evaporation of water? Let us examine this in Practical 2.3. ### 2.3 Practical: Factors Affecting Rate of Evaporation #### Aim * To investigate the factors affecting the rate of evaporation of water. #### Apparatus and Material per Class * Filter paper * Petri Dish * Dropper * Electronic balance * Stopwatch * Airtight container * Moisture absorbing pack * Hygrometer * Per Group: * Filter paper * Petri dish * Dropper * Electronic balance * Stopwatch * Heat pack * Hand-held Electric fan * Infrared thermometer #### Part I: Humidity * **Setting a question:** How does ______*humidity*_______ affect the rate of evaporation of water? * **Identifying variables:** * **Independent Variable:** The humidity * **Dependent Variable:** Mass of water evaporated * **Controlled Variables:** * Air speed * Amount of water added * Temperature * Exposed surface area to air * Type and size of filter paper #### Carrying out the experiment 1. Put two pieces of filter paper on two Petri dishes. Label the Petri dishes A and B. 2. Use a dropper to add three drops of water to each piece of filter paper. 3. Measure the mass of each set-up (M₁) with an electronic balance. 4. Put set-up A, a moisture absorbing pack and a hygrometer in an airtight container. The moisture absorbing pack lowers the humidity in the container. Put set-up B and a hygrometer in another airtight container. 5. Leave both containers for 30 minutes. Record the humidity in each container. Measure the mass of each set-up again (M₂). Find the mass of water evaporated in each set-up by calculating the difference in the mass of the set-up before and after the experiment. #### Recording the Results |Set-Up | Mass of Set-Up at the beginning (M₁) (g) | Mass of Set-Up after 30 minutes (M₂) (g) | Mass of water evaporated (g) | |---|---|---|---| | Set-Up A (Humidity: ) | | | | | Set-Up B (Humidity: ) | | | | #### Drawing a conclusion: * The rate of evaporation of water is ______ *(higher/lower)* _______ when the humidity is higher. #### Part II Temperature * **Setting a question:** How does _________ *temperature*__________ affect the rate of evaporation of water? * **Identifying variables:** * **Independent Variable:** Temperature * **Dependent Variable:** Mass of water evaporated * **Controlled Variables:** * Air speed * Amount of water added * Humidity * Exposed surface area to air * Type and size of filter paper #### Carrying out the experiment: 1. Put two pieces of filter paper on two Petri dishes. Label the Petri dishes C and D. 2. Use a dropper to add three drops of water to each piece of filter paper. 3. Measure the mass of each set-up (M₃) with an electronic balance. 4. Place an unopened heat pack under set-up C and an opened heat pack under set-up D. 5. Use an infrared thermometer to measure the temperatures of set-ups C and D. Record the temperatures of both pieces of filter paper. 6. Leave both set-ups in air for 30 minutes. Measure the mass of each set-up again (M₄). Find the mass of water evaporated in each set-up by calculating the difference in the mass of the set-up before and after the experiment. #### Recording the results |Set-Up | Mass of Set-Up at the beginning (M₃) (g) | Mass of Set-Up after 30 minutes (M₄) (g) | Mass of water evaporated (g) | |---|---|---|---| | Set-Up C (Temperature: ) | | | | | Set-Up D (Temperature: ) | | | | #### Drawing a conclusion: * The rate of evaporation of water is ______ *(higher/lower)* _______ when the ________ *temperature*________ is higher. #### Part III: Air speed * **Setting a question:** How does _______ *air speed* ________ affect the rate of evaporation of water? * **Identifying Variables:** * **Independent Variable:** Air speed * **Dependent Variable:** Mass of water evaporated * **Controlled Variables:** * Humidity * Temperature * Amount of water added * Exposed surface area to air * Type and size of filter paper #### Carrying out the experiment: 1. Write down the steps of the experiment in the space below. Draw a labelled diagram of your set-up. 2. Show your set-up to your teacher. Carry out the experiment after getting approval from your teacher. #### Recording the results: Record your results in the space below. #### Drawing a conclusion: #### Big Science Ideas * **Doing experiments to collect evidence:** We made observations and collected data in Practical 2.3. They provided evidence for our conclusion about how different factors affect the rate of evaporation. #### Did you know? * **Diatomite bath mat:** Have you ever used a diatomite bath mat (Fig 2.14)? The mat can absorb water in seconds and is quick-drying. Do you know how it works? Diatomite is the fossilized remains of a kind of algae. It has many tiny pores (Fig 2.15). When water comes into contact with diatomite, it gets into the tiny pores. As the total surface area of the pores is very large, water evaporates very quickly. This makes diatomite dry in a short time. #### Key Point * The rate of evaporation of water is higher when: * The surface area exposed to air is ______ *(larger/smaller)*______. * The humidity is ______ *(higher/lower)* ______. * The temperature is ______ *(higher/lower)* ______. * The air speed is ______ *(higher/lower)* ______. #### Did you know? * We mention on page 90 that alcohol evaporates more quickly than water. Can you think of a fair test to find out if this is really the case? ### 2.2 Quick Check * **In which of the following conditions will wet clothes dry slowly?** * (1) Folding the clothes * (2) Low humidity * (3) Exposing to sunlight * **The following containers hold the same amount of water and are left under the sun. After several hours, which container would have the least amount of water?** *(Diagram of 4 containers).* ### Section Summary 2.2 * **The water cycle involves the following processes:** * **Evaporation:** Water in the sea, rivers and on land evaporates and becomes water vapor. * **Precipitation:** Water droplets in the cloud fall as rain. * **Condensation:** The water vapor cools down and condenses, forming clouds. * **Transportation:** Clouds may be carried to other places by the wind. * **The rate of evaporation of water is higher when:** * The surface area exposed to air is larger. * The humidity is lower. * The temperature is higher. * The air speed is higher. ### Section Exercise 2.2 #### Level 1 * **Questions 1 to 3: Refer to the information below. Write ‘T’ for a true statement and ‘F’ for a false statement in the boxes provided.** * *Joe prepares the set-up on the right. The set-up is placed under the sun. After several hours, liquid P is collected in the glass.* *(Diagram showing a large bowl with water, a smaller glass bowl inside that, with a plastic sheet on top, and an eraser on top of that)* * **1.** The formation of liquid P involves boiling and condensation. **F** *p. 95* * **2.** Liquid P is colorless. **T** *p. 95* * **3.** Liquid P can be collected in the glass more quickly when the colored water is heated. *p. 95* #### Level 2 * **4.** Grace finds that it takes a long time to dry her hair without using a hairdryer. * a) Give TWO reasons to explain why wet hair dries more quickly under hot hair from a hairdryer. *(2 marks)* * b) Grace usually separates her hair with her fingers when using the hairdryer. Explain why. *(1 mark)* *(Diagram of a woman with a hairdryer)* *p. 101*