Kerala Syllabus Class 7 Basic Science: Chapter 02 Acids and Bases - Questions and Answers
Questions and Answers for Class 7 Basic Science (English Medium) ആസിഡുകളും ബേസുകളും | Text Books Solution Basic Science (English Medium) Chapter 02 Acids and Bases - Teaching Manual | Teachers Handbook
ഈ അധ്യായത്തിന്റെ Teachers Handbook, Teaching Manual എന്നിവ ഡൗൺലോഡ് ചെയ്യാനുള്ള ലിങ്ക് ചോദ്യോത്തരങ്ങളുടെ അവസാനം നൽകിയിട്ടുണ്ട്.
ഈ ബ്ലോഗ് ഉടമയുടെ രേഖാമൂലമുള്ള അനുമതിയില്ലാതെ ഈ ബ്ലോഗിൽ നൽകിയിരിക്കുന്ന ചോദ്യോത്തരങ്ങൾ, ഇതേരീതിയിലോ പി.ഡി.എഫ് രൂപത്തിലോ, മറ്റേതെങ്കിലും ഡിജിറ്റലോ, പ്രിന്റഡ് ഉൾപ്പെടെയുള്ള ഏതെങ്കിലും രൂപങ്ങളിലേക്കോ മാറ്റി മറ്റൊരു വെബ്സൈറ്റിലോ, ബ്ലോഗിലോ, യുട്യൂബ്, സോഷ്യൽ മീഡിയാ ഗ്രൂപ്പുകളിലോ ഉൾപ്പെടെ ഒരിടത്തും പ്രചരിപ്പിക്കാൻ പാടില്ലാത്തതാകുന്നു.
Std 7: Basic Science Chapter 02: Acids and Bases - Questions and Answers
♦ In the experiment mentioned in Jinu’s diary, the teacher must have added something to the second tumbler. Which among the following did the teacher add to turn the pink liquid into yellow? (Textbook Page No: 28)
Put a tick (✔) mark on the appropriate boxes, based on the experiment you have done.
• Ash suspension
• Lemon juice ✔
• Salt solution
• Vinegar ✔
• Tamarind water ✔
• Baking soda solution
♦ Do the substances that turned Pathimugam water into yellow have anything common in their taste?
Yes, they all have a sour taste. The sour taste is due to the presence of some acids in them.
♦ Take blue and red litmus papers from the school laboratory. Dip blue and red litmus papers in these liquids. Tabulate your observations in the Science Diary.
• Soap water
• Lemon juice
• Clear baking soda solution
• Clear lime water
• Vinegar
• Buttermilk
• Tamarind water
• Clear ash suspension
• Lemon juice
• Vinegar
• Buttermilk
• Tamarind water
♦ Which liquids turned red litmus into blue?
• Lime water
• Soap water
• Clear baking soda solution
• Clear ash suspension
♦ What are Acids?
Acids are substances that turn blue litmus into red.
♦ What are Bases
Substances that turn red litmus into blue are bases.
♦ What are Indicators?
Indicators are substances that help to identify acids and bases by changing their colour. Litmus paper is an indicator.
♦ In addition to the blue and red litmus papers name two other indicators that are commonly used in laboratories.
Phenolphthalein and Methyl Orange.
♦ Observe the change in colour when two or three drops of Phenolphthalein are added to various acids and bases. Similarly, add two or three drops of Methyl Orange in acids and bases and observe the change. Tabulate the colour change.
Methyl Orange
• Which substances can be used as indicators of bases?
Phenolphthalein
♦ All acids have ---------- taste.
sour
♦ All bases have ----------- taste.
alkaline
♦ Dip your fingers in each liquids in the Science Kit and rub the fingers as shown in the picture. (Textbook Page No: 32)
Which liquids feel slippery? List them.
• Soap water
• Baking soda solution
• Lime water
• Ash suspension
♦ Identify the common properties of acids and bases. Tabulate them.
| Acids | Bases |
| • Sour Taste • Turn blue litmus red | • Alkaline Taste • Turn red litmus blue • Slippery |
♦ Which among the following substances can turn blue litmus red? List them.
• Orange juice
• Rice soup
• Black tea
• Bilimbi (Irumban puli) juice
• Grape juice
• Tomato juice
• Coconut water
| In my opinion, liquids that can turn blue litmus red | Reason |
| • Orange juice • Bilimbi (Irumban puli) juice • Grape juice • Tomato juice | These have sour taste so they contain acids. Acids turn blue litmus red. |
♦ Acids that are found in food items.
| Food item | Main acid present |
| • Buttermilk, Curd • Vinegar • Lemon • Tamarind • Apple • Gooseberry • Tomato | • Lactic acid • Acetic acid • Citric acid • Tartaric acid • Malic acid • Ascorbic acid • Oxalic acid |
♦ How does milk turn acidic when it becomes curd?
A little curd is added to milk to turn it into curd. Curd contains a bacteria called Lactobacillus. The lactic acid that is produced when these bacteria nourish themselves with milk, gives curd its sour taste.
♦ Acids and bases used in laboratories.
| Acids | Bases |
| • Hydrochloric acid • Nitric acid • Sulphuric acid • Acetic acid | • Calcium hydroxide (Lime) • Sodium hydroxide (Caustic soda) • Potassium hydroxide (Caustic potash) |
♦ What precautions should we take to avoid accidents while handling chemicals?
• Avoid spilling on body parts
• Don't touch with hands
• Don't smell
• Don't taste
• Use a dropper while taking out acid from a bottle
• Use a holder while using a test tube
♦ What should we do if acid spills?
Strong acids can absorb water and liberate heat. They can cause burns if they get spilled on the body. Pouring cold water on the affected area for a long time is the first aid for this. If the burn is severe, the person should be taken to hospital.
♦ Take acids and bases in separate test tubes. Observe and tabulate the colour changes that occur when various indicators are added to them.
• Objective - Identify the gas produced when the acid reacted with metal.
• Materials required - Acetic acid, Magnesium, test tube
• Procedure - Fill a quarter of a test tube with vinegar (dilute acetic acid). Put three or four small strips of magnesium ribbon into it. Close the mouth of the test tube with your thumb for a while. Tilt the test tube slightly. Remove your thumb after bringing a burning matchstick to the mouth of the test tube.
• Observation - A colourless and odourless gas evolved from the test tube. The gas burned up with a pop sound in the presence of fire.
• Inference - Acetic acid reacts with magnesium, and hydrogen gas is formed.
When acids react with metals, hydrogen is produced. Hydrogen is a flammable gas.
♦ General Properties of Acids
• Has sour taste
• Turns blue litmus red
• Reacts with metals to produce hydrogen
♦ Explain the reason for the following situations?
• Metal containers are not used to store pickles.
Pickles contain acids. Acids react with metals. This may cause health issues. So pickles are usually stored in glass jars.
• Earthen vessels are commonly used to cook dishes with curd and buttermilk.
Curd and buttermilk contain lactic acid. Lactic acid reacts with metallic vessels and causes corrosion. This will cause health problems. So Earthen vessels are suitable for cooking dishes with curd and buttermilk.
♦ What are the uses of vinegar at home?
• In pickles
• In cooking
• For preservation and food processing
• To remove stains from upholstery and carpets
• To remove labels and stickers by dissolving adhesives
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♦ Some acids and their uses are listed in the table below. Complete the list
| Acids | Uses |
| • Acetic acid | • Pickle making, cooking, Food processing |
| • Formic acid | • For thickening latex |
| • Citric acid | • To make drinks |
| • Sulphuric acid | • In motor vehicle batteries and for manufacturing chemical fertilisers |
| • Nitric acid | • To make chemical fertilizers, paints and dyes |
| • Tannic acid | • To make leather and Ink |
| • Carbonic acid | • In soft drinks and soda water |
♦ Uses of Bases
| Bases | Uses |
| • Calcium hydroxide | • Glass manufacturing, to reduce the acidity of soil |
| • Sodium hydroxide | • To make soap, paper and rayon |
| • Potassium hydroxide | • To make soft soap |
| • Aluminium hydroxide, Magnesium hydroxide | • In medicines |
♦ Analyse the table and find out the following.
• Which is the base used to make soap?
Sodium hydroxide, Potassium hydroxide
• Which are the bases used in medicines?
Aluminium hydroxide, Magnesium hydroxide
♦ Write the Method of preparation of Soap
Materials required (To make 20 soaps):
Caustic soda 180 grams, coconut oil 1 Kilogram, water 350 millilitres, Sodium silicate 100 grams, stone powder 100 grams, colour and perfume.
Method of preparation
Take water in a steel bowl and dissolve caustic soda in it. A large amount of
heat is liberated when caustic soda dissolves in water. After the solution cools
down, slowly pour it in a flat vessel containing coconut oil. Stir it well while
pouring. Then add sodium silicate and stone powder one by one to increase the hardness and quantity of the soap. Colour and perfume can be added to the soap to make it more attractive and fragrant. Stir the mixture continuously till it gets thickened. Pour the thick mixture into the mould. After solidification, remove the soap from the mould. It can be used after two weeks.
♦ Which are the coloured parts of plants that you know? List them.
• Red spinach
• Blue coloured Clitoria (Sanghupushpam)
• Red cabbage
• Beetroot
• Turmeric
• Grape juice
• Pathimugam
♦ Prepare either paper strips rubbed with each of the above vegetables, their juices or the coloured liquids obtained by boiling them in water. Test them with the acids available at home. Repeat the experiment with the bases also available at home. Write down the observations.
| Part of plant | Natural colour | Colour in acid | Colour in base |
|---|---|---|---|
| Sanghupushpam | Blue | Pink | Light green |
| Red cabbage | Purple red | Reddish pink | Bluish green |
| Beetroot | Dark pink | Violet | Greenish yellow |
| Turmeric | Yellow | Yellow | Red |
| Grape juice | Purple | Red | Greenish yellow |
| Pathimugam | Pink | Yellow | Pink |
Let’s Assess
1. Which among the following can be used as an indicator of acid?
a. Turmeric
b. Pathimugam
c. Red litmus paper
d. Phenolphthalein
Answer: b. Pathimugam
2. Which acid is used in automobile batteries?
a. Hydrochloric acid
b. Nitric acid
c. Sulphuric acid
d. Formic acid
Answer: c. Sulphuric acid
3. Among the liquids in the three beakers placed on the table, the first one is water, the second is an acid and the third is a base. Is it right to identify them by touching, tasting or smelling? Why? Suggest a method to identify each of them.
Answer: No, touching, tasting, and smelling chemicals is dangerous. We can identify acids and bases by using litmus paper. Acids turn blue litmus red, and bases turn red litmus blue. If both the litmus do not change their colour the liquid will be water.
4. In the laboratory metalic caps are not used for glass bottles containing acids. Explain the reason for this.
Acids react with metals and corrode metals. So metallic caps are not used for glass bottles containing acids.
5. Examine the statements given below. Classify them on the basis of
properties of acids and bases.
a. Has sour taste
b. Turns to pink when phenolphthalein is added
c. Slippery
d. Turns to pink when methyl orange is added
e. Turns the colour of Pathimugam water into yellow
f. Red litmus turns blue
g. Reacts with metals to produce hydrogen
h. Has alkaline taste
Answer:
• Properties of acids
a. Has sour taste
d. Turns to pink when methyl orange is added
e. Turns the colour of Pathimugam water into yellow
g. Reacts with metals to produce hydrogen
• Properties of bases
b. Turns to pink when phenolphthalein is added
c. Slippery
f. Red litmus turns blue
h. Has alkaline taste
6. You have learnt about various indicators to identify acids and bases.
Complete the table below.
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