Page 37 - prim 5 booklet 2025 Summary
P. 37

Delta Modern Language Schools
Science department
Grade 5
1st term 2024 -2025

Evidences that describe chemical changes:-

1- Unexpected change in color.   Mixing iodine with cornstarch.(producing a new

substance with dark blue color)

2- Formation of gas bubbles.     When mixing vinegar with baking soda, (gas bubbles

appear).

3- Formation of strong odor.     Leaving a cup of milk out of the fridge. (You see

chunks in the milk and smell a bad odor).

                                 Desalination

    Although about 70% of the Earth’s surface is covered by oceans, but we can’t drink the
    water of oceans and seas because it is a mixture of water, salt, other minerals, gases, living
    and dead organisms. We can use desalination processes to drink this water.

• Desalination: It is a process of removing salt from water.

➢ We can separate fresh drinkable water from the mixture of ocean’s water by:-

1-Filtration:-

- It removes any large material such as seaweed, shells and fish.
- Water, salts, minerals and gases would pass through filters, that

  make water still undrinkable.

2-Evaporation:-

- When boiling the filtered water, water vapor rises up leaving salts and other minerals.
- When cooling the water vapor, it is turned into liquid water and it is safe to drink it.

 Problems of desalination:-

 ➢ It requires a lot of energy.
 ➢ It is very expensive process.
 ➢ It may lead to environmental problems such as:-
 - Small marine organisms can be hurt due to sucking of water
 into the desalination plants.
 - The water that contains a very big amount of salt that is pumped back to oceans after
 desalination can be dangerous to the marine life.

   Note:- Egypt has over 80 desalination plants.

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