CBSE Class 7 Science Advanced Chemistry Chemistry in Daily Life MCQs Set 01

Answer: (c) zinc

Explanation:
1. Iron is strong and is used as steel in bridges and towers.
2. Aluminium (as alloys), and copper, are strong and drawn into wires.
3. Zinc is brittle and does not show clear malleability or ductility, so it has the least tensile strength: zinc.

Teacher's Note:
1. Tensile strength tells how much pulling a metal can take before it breaks.
2. Zinc is the weak one in this list, which is also why it is not used for wires.

Answer: (d) magnesium

Explanation:
1. Brass is copper and zinc; bronze is copper, zinc and tin; magnalium is aluminium and magnesium.
2. Magnesium is a pure element (a metal), so magnesium is not an alloy.

Teacher's Note:
1. An alloy is a mixture of a metal with other metals, or sometimes a little non-metal.
2. Be careful: magnalium and magnesium sound alike but only one is an alloy.

Answer: (b) tin

Explanation:
1. Tinning means coating articles with tin.
2. So the element used is tin; it coats food cans and vessels of copper and iron.

Teacher's Note:
1. The name of the process often gives away the element.
2. Compare: galvanization uses zinc, tinning uses tin.

Answer: (b) iron and zinc

Explanation:
1. Galvanization is coating iron with zinc.
2. The two metals are iron and zinc.

Teacher's Note:
1. Zinc is more reactive than iron, so it protects the iron underneath.
2. Learn galvanization as iron + zinc.

Answer: (c) very light and possesses high tensile strength

Explanation:
1. Aircraft frames need a material that is light yet strong.
2. Duralumin (95% aluminium) is very light and has high tensile strength, so the reason is (c).
3. It is not a bad conductor, so (a) and (d) are wrong.

Teacher's Note:
1. Match the property to the job: aircraft means low weight with strength.
2. Do not pick 'all of the above' without checking every option.

Answer: (b) helium

Explanation:
1. The noble gases are helium, neon, argon, krypton, xenon and radon.
2. Only helium is in the list.

Teacher's Note:
1. Noble gases are inert (very unreactive).
2. Learn the six names in order of increasing atomic size.

Answer: (d) iron, chromium, carbon and nickel

Explanation:
1. Stainless steel is iron (83%), chromium (15%), carbon (1%) and nickel (1%).
2. So the answer is iron, chromium, carbon and nickel.

Teacher's Note:
1. Chromium is what stops stainless steel from rusting.
2. There is no copper in this alloy.

Answer: (d) sodium chloride, sodium iodide or potassium iodide

Explanation:
1. Table salt is sodium chloride with a small amount of sodium iodide or potassium iodide added.
2. Free iodine is not added, so the answer is (d).

Teacher's Note:
1. The added iodide prevents goitre.
2. Iodine (the element) is not mixed in, only its compounds.

Answer: (a) calcium carbonate

Explanation:
1. Limestone and marble are both calcium carbonate, \(\ce{CaCO3}\).
2. Calcium oxide is lime, and calcium sulphate is gypsum.
3. So the answer is calcium carbonate.

Teacher's Note:
1. Heating limestone gives lime and carbon dioxide.
2. Marble has the same chemical formula as limestone.

Answer: (c) silicon dioxide

Explanation:
1. Sand is a natural form of silicon dioxide, \(\ce{SiO2}\).
2. Sodium silicate is water glass and is a different compound.
3. So the answer is silicon dioxide.

Teacher's Note:
1. Sand is a compound, not the element silicon.
2. It is the raw material for glass and cement.

Answer: (d) copper

Explanation:
1. Cables need a metal with very high electrical conductivity.
2. Silver is best but costly; copper is the second best conductor.
3. So the most suitable metal here is copper.

Teacher's Note:
1. Aluminium is used for high-voltage overhead lines because it is light.
2. For cables, conductivity decides, and copper wins in this list.

Answer: (d) distillation

Explanation:
1. The steps are: evaporation of sea water, crude salt formation, dissolution in water, and recrystallization.
2. Distillation is not used, so the answer is distillation.

Teacher's Note:
1. Distillation would collect the water and not the salt.
2. Remember the order: evaporate, dissolve, recrystallize.

Answer: (b) poor electrical conductivity

Explanation:
1. Non-stick pans use silicone because it withstands heat, does not stick and resists chemicals.
2. Electrical conductivity has nothing to do with cooking, so poor electrical conductivity is the property not used.

Teacher's Note:
1. Ask which property a frying pan needs.
2. Poor conductivity is used for insulators, not pans.

Answer: (a) vegetable oil

Explanation:
1. Fats give the largest amount of energy per gram.
2. Vegetable oil is a fat, so the answer is vegetable oil.

Teacher's Note:
1. Glucose gives quick energy, but fat gives the most.
2. Fats are the energy store; carbohydrates are the instant source.

Answer: (a) cement mortar

Explanation:
1. Cement mortar (cement and sand, 1 : 4) is used for plastering and joining bricks.
2. Concrete and RCC are used for casting roofs, pillars and beams.
3. So the answer is cement mortar.

Teacher's Note:
1. Plastering needs a smooth thin paste, which is why gravel is not used.
2. Concrete has gravel in it, so it is not suited for plastering.

Answer: (d) All the above.

Explanation:
1. Thermoplastics soften on heating and can be remoulded again and again, with no chemical change.
2. Thermosetting plastics, once set, cannot be softened again.
3. All three statements are true, so the answer is all the above.

Teacher's Note:
1. Think of thermoplastic as reusable and thermosetting as set for ever.
2. Check each statement before choosing 'all the above'.

Answer: (a) glycerine

Explanation:
1. Vegetable oil + sodium hydroxide gives soap + glycerine.
2. Soap is the main product, and glycerine is the by-product.

Teacher's Note:
1. Sodium hydroxide and oil are the starting materials, not products.
2. The salt of the fatty acid is the soap itself.

Answer: (c) supercooled liquid

Explanation:
1. Molten glass is cooled slowly and its viscosity rises so much that it stops flowing.
2. In this chapter's description, glass is a supercooled liquid that only looks like a solid.

Teacher's Note:
1. The key idea is that glass has no sharp freezing point.
2. It looks solid because its viscosity becomes very high.

Answer: (b) 2413

Explanation:
1. Plaster of Paris \(\ce{CaSO4.1/2H2O}\) has 4.5 oxygen atoms per formula unit (4 + ½).
2. Glucose \(\ce{C6H12O6}\) has 6; sugar \(\ce{C12H22O11}\) has 11; starch \(\ce{(C6H10O5)_n}\) has 5n (many).
3. Order: 2, 4, 1, 3, so the answer is 2413.

Teacher's Note:
1. Count the oxygen atoms in each formula first.
2. Starch is a polymer, so it has the most.

Answer: (a) 2413

Explanation:
1. First the raw mixture is pulverized (2).
2. It is then heated to 1500 to 1600 °C (4), forming clinkers (1).
3. Finally gypsum is added (3).
4. The order is 2413.

Teacher's Note:
1. Clinkers form because of the heating, so heating comes before clinkers.
2. Gypsum is the last ingredient, added to the ground clinker.

Answer: (b) carbon, hydrogen and oxygen

Explanation:
1. Starch is a carbohydrate with formula \(\ce{(C6H10O5)_n}\).
2. It contains carbon, hydrogen and oxygen.

Teacher's Note:
1. All carbohydrates contain only C, H and O.
2. Nitrogen is present in proteins, not in starch.

Answer: (d) All the above.

Explanation:
1. An alloy is a uniform mixture of metals, and may include a little non-metal such as carbon.
2. Alloys are generally stronger and more corrosion resistant.
3. All three statements are true: all the above.

Teacher's Note:
1. Steel is an example of an alloy containing carbon.
2. Alloying improves properties; that is why it is done.

Answer: (d) sodium lauryl sulphate

Explanation:
1. Sodium stearate is a soap (sodium salt of a fatty acid).
2. Sodium chloride and sodium carbonate are not cleansing agents of this kind.
3. Sodium lauryl sulphate is a sodium salt of an alkyl hydrogen sulphate, so it is the detergent.

Teacher's Note:
1. Soaps come from fatty acids; detergents come from alkyl hydrogen sulphates.
2. Remember the name 'sodium lauryl sulphate'.

Answer: (c) cement, sand and water

Explanation:
1. Cement mortar is cement and sand (1 : 4) made into a thick paste with water.
2. So mortar is cement, sand and water.

Teacher's Note:
1. Gravel appears in concrete, not in mortar.
2. Mortar joins bricks and is used for plastering.

Answer: (d) all of these

Explanation:
1. Heating limestone gives quicklime.
2. Limestone is also a raw material of glass and of cement.
3. So the answer is all of these.

Teacher's Note:
1. Limestone is one of the most useful raw materials in industry.
2. All three uses are in this chapter.

Answer: (d) lithium iodide

Explanation:
1. Iodized salt is common salt with sodium iodide or potassium iodide.
2. Lithium iodide is not added, so the answer is lithium iodide.

Teacher's Note:
1. Only sodium and potassium iodides are added to salt.
2. Note that common salt itself is the main part of it.

Answer: (d) 1 : 1

Explanation:
1. The fusible alloy of lead and tin used for fuse wire has equal masses of the two metals.
2. So the ratio is 1 : 1.

Teacher's Note:
1. Fusible means easily melted.
2. Equal masses of lead and tin give a low-melting fuse wire.

Answer: (b) vegetable oil

Explanation:
1. Fats give the maximum energy.
2. Vegetable oil is a fat, so the answer is vegetable oil.

Teacher's Note:
1. Starch and glucose are carbohydrates, and albumin is a protein.
2. Fat is the energy reservoir of the body.

Answer: (c) potassium hydroxide

Explanation:
1. Soft or liquid soap is made from vegetable oil and potassium hydroxide.
2. So the answer is potassium hydroxide.
3. Pumice stone is a filler for scouring soap, and alcohol is used for transparent soap.

Teacher's Note:
1. Hard soaps use sodium hydroxide, soft soaps use potassium hydroxide.
2. Link each soap to its raw material.

Answer: (d) silver

Explanation:
1. Silver iodide (and silver nitrate) is used to seed clouds for artificial rain.
2. So the metal is silver.

Teacher's Note:
1. Cloud seeding gives particles around which raindrops form.
2. Silver compounds are also used in photographic film.

Answer: (d) making electric transmission cables

Explanation:
1. Statues, utensils and shells use alloys such as brass or bronze.
2. Electric cables need very pure copper because impurities reduce conductivity.
3. So the answer is making electric transmission cables.

Teacher's Note:
1. Pure metal gives the best conductivity.
2. Alloys are chosen for strength, not for conduction.

Answer: (b) soft nature

Explanation:
1. Crucibles need heat and chemical resistance; electrodes need electrical conductivity.
2. Softness is useful in pencils, but not in these two applications.
3. So the property not used is soft nature.

Teacher's Note:
1. Use the property that matches each job.
2. Softness is what allows graphite to mark paper.

Answer: (c) A – c, B – d, C – e, D – a

Explanation:
1. A: cleaning metal surfaces uses hydrochloric acid, c.
2. B: the insecticide is blue vitriol \(\ce{CuSO4.5H2O}\), d.
3. C: the Taj Mahal is built of marble, calcium carbonate, e.
4. D: casting toys and statues uses plaster of Paris, a.
5. So the match is A – c, B – d, C – e, D – a.

Teacher's Note:
1. Take the entries one by one and strike them out.
2. Marble and limestone share the same formula.

Answer: (a) a solution of glucose

Explanation:
1. Glucose is the simplest carbohydrate and is absorbed quickly.
2. So a solution of glucose gives instant energy.

Teacher's Note:
1. This is why glucose is given to tired or dehydrated patients.
2. Milk gives energy too, but not so quickly.

Answer: (c) RCC

Explanation:
1. Pillars carry a heavy load.
2. RCC (concrete reinforced with structural steel) is the strongest and most durable, so the answer is RCC.

Teacher's Note:
1. Steel inside the concrete resists pulling forces.
2. Mortar and pure cement are too weak for pillars.

Answer: (d) bakelite

Explanation:
1. Polyethylene, nylon and terylene are thermoplastics.
2. Bakelite is thermosetting, so the answer is bakelite.

Teacher's Note:
1. Bakelite is used for switches and handles of cookware.
2. Learn the four thermosetting examples: urea-formaldehyde, polyurethane, melamine and bakelite.

Answer: (c) sodium lauryl sulphate

Explanation:
1. Soaps (sodium or potassium salts of fatty acids) form scum with hard water.
2. Sodium lauryl sulphate is a detergent and forms soluble compounds, so the answer is sodium lauryl sulphate.

Teacher's Note:
1. Detergents work in hard water; soaps do not.
2. Scum is the curdy precipitate of calcium and magnesium compounds.

Answer: (a) 2134

Explanation:
1. The raw materials are mixed first (2).
2. Cullet is added (1), then colouring pigments (3).
3. After melting and shaping, the glass is annealed (4).
4. The order is 2134.

Teacher's Note:
1. Annealing is always the last step.
2. Cullet helps melting, so it goes in before the melt is made.

Answer: (a) 25413

Explanation:
1. Sea water is evaporated (2) to give crude salt (5).
2. The crude salt is dissolved in water (4) and recrystallized (1).
3. Finally iodides are added (3).
4. The order is 25413.

Teacher's Note:
1. Purification comes before the addition of iodides.
2. Crude salt is the first solid obtained.

Answer: (b) 2134

Explanation:
1. Mix limestone and clay (2), then pulverize (1).
2. Heat to form clinkers (3).
3. Grind the clinkers and add gypsum (4).
4. The order is 2134.

Teacher's Note:
1. You cannot grind before you mix the raw materials.
2. Gypsum is added only at the end.