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.
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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