Page 37 - prim 5 booklet 2025 Summary hajar_Neat 3

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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