Changes of the Matter

Changes of the Matter

Physical change:
It is a change in the shape of the matter without any change in its structure.

Examples of physical changes:
1- Crushing of sugar.
2- Changing of water into ice or vapour.
3- Melting of wax.
Chemical change:
It is a change in the structure of matter producing another substance or substances of different properties.

Examples of chemical changes:
1- Burning of sugar.
2- Burning of paper.
3- Iron rust.
Q1: Give reasons:
1- Melting of wax is an example of physical changes.
Because the appearance is changed but the structure did not change.

2- Burning of sugar is an example of chemical changes.
Because the structure is changed giving a new substance with new properties.

3- Chemical change has a change in properties of matter.
Because it leads to the formation of new substances that have new properties.

Q2: What happens in the following cases?
1- Putting a piece of iron wire in water for several days, then exposing it to air.
" A layer of iron rust is formed.

2- Putting a cube of sugar in a burning spoon and heating it strongly.
" Sugar is burned and changed to another substance that has different properties.

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Solution

Solution

The solution:
It is a homogeneous system that consists of a solvent (as water) and a solute (as table salt).

" A solution requires a solvent and a solute.
" Speed of dissolution increases by stirring and heating.
" The solution is a mixture, in which its components (the solute and solvent) can be separated by physical means.

Examples of solutions:
1- Table salt in water.
2- Sugar in water.


Q1: Give reason:
Salt solution in water is a mixture not a compound.
" Because its components can be separated easily by evaporation.

Q2: What happens in the following cases?

1- Stirring some of chalk powder in a beaker containing water.
" Chalk does not dissolve in water.

2- Exposing a solid surface to evolved water vapour.
" Water vapour is condensed .

Alkalis, acids and salts

Alkalis, acids and salts

A: Alkalis:
Properties of alkalis :
1- Alkalis turn the colour of red litmus paper into blue.
2- Dilute solutions of alkalis have the soft feel of soap.
3- Alkalis react with vegetable oils to form soap.

Examples of alkalis:
1- Caustic soda (sodium hydroxide).
2- Caustic potash (potassium hydroxide).
3- Ammonia solution (ammonium hydroxide).

B: Acids:
1- Acids change the colour of blue litmus paper to red.
2- Dilute acids have a sour taste.
3- Acids react with sodium carbonate or sodium bicarbonate and carbon dioxide gas evolves which makes lime water cloudy (turbid).

Examples of Acids:
1- Vinegar (dilute acetic acid).
2- Lemon juice (citric acid)
3- Hydrochloric acid.
4- Nitric acid.
5- Sulphuric acid.

C: Salts:
Salt solutions have neutral effect on red and blue litmus papers.

Examples of salts:
1- Sodium chloride (table salt).
2- Sodium carbonate.
3- Sodium bicarbonate.
4- Calcium carbonate (lime stone - chalk - marble).

Q1: Give reasons:
1- Vinegar changes the colour of blue litmus paper to red.
" Because vinegar is the acetic acid, which changes the blue litmus, paper to red.

1- On adding lemon juice to sodium carbonate, effervescence takes place and lime water becomes milky.
Because carbon dioxide gas evolves.

2- An alkaline solution can be tested using a red litmus paper.
Because the alkalis change the colour of red litmus to blue.

3- An acidic solution can be tested using a blue litmus paper.
Because the acids change the colour of blue litmus paper to red.

4- Carbon dioxide gas can be tested using lime water.
" Because carbon dioxide turns clear lime water to cloudy.

Q2: What happens in the following cases?
1- Adding caustic soda solution to vegetable oil with continuous stirring.
" Soap is formed.

2- If you put two litmus papers, one is red and the other is blue in a beaker containing table salt solution.
" The colour of the two litmus papers does not change.
3- On adding vinegar to a solution of sodium bicarbonate.
" Effervescence takes place and bubbles of carbon dioxide gas evolve.

4- If you put two litmus papers, one is red and the other is blue in a beaker containing caustic potash.
" The colour of red litmus paper changes to blue while the blue paper does not change.

5- On passing carbon dioxide gas in clear lime water.
" Lime water becomes cloudy (milky).

6- If put two litmus papers, one is red and the other is blue in a beaker containing lemon juice.
" The colour of blue litmus paper changes to red while the red one does not change.

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