YADNYA e-Learning

Monday, March 1, 2021

7th Std Science 15 Materials we Use l Question and Answer

YADNYA e-Learning

Science Studies - 7th Standard

15. Materials we Use

Question And Answer

1. Fill appropriate terms in the blanks.

(white cement, soap, detergent, wearing of bones, tooth decay, hard, soft, Portland, fatty acid)

(a) The substance that helps water to remove dirt from the surface of materials is called detergent.

(b) Fluoride is used in toothpaste to prevent tooth decay.

(d) Synthetic detergents can be used in hard water as well.

(e) For construction purposes Portland cement is the most commonly used cement.

2. Write answers to the following questions.

(a) How does the use of a detergent help to clean soiled clothes ?

Ans: Detergent is a cleansing agent that combines with the impurities to make them more soluble and therefore wipe them away. A molecule of detergent consists of two ends. One of its ends is attracted towards the water while the other holds on to the dirt. This results in the mixing of dirt and water. Due to the ability to get attached to both oil and water, detergent molecule spreads easily. This property of a substance expanding on a surface is known as surface activity and the substance is known as surfactant. One of the effects of surface activity is lather formation.This action of detergent molecule results in the removal of dirt and stains from the clothes.

(b) How will you check with the help of soap powder whether water is hard ?

Ans: Soap can be used to check wether sample of water is hard or soft. Soaps do not give lather with hard water instead form scum whereas they give lather with soft water. If we do not get lather in water while using soap, we can say it is hard water.

Ans: The important ingredients of a toothpaste are abrasives, water and fluoride. Abrasives such as calcium carbonate and calcium hydrogen phosphates help to remove the dirt on teeth and also helps to polish them. Fluoride is the most common active ingredients used to prevent decay of our teeth. It helps in strengthening of bones and the enamel which covers the teeth.

(d) What are the ingredients of cement ?

Ans: The ingredients of cement are lime (CaO), clay, silica along with some other oxides of aluminium, iron and magnesium. Gypsum (CaSO4, 2H2O) is usually added to regulate the setting rate of cement.

(e) What will happen if cement is not used in making concrete ?

Ans: Concrete is a mixture of cement, water, sand and gravel. Cement helps in making the structures strong and leak proof. If cement is not mixed in concrete, the structures made using concrete will not be strong and leakproof and thus will have the chances of falling down.

(f) Make a list of detergents that you use.

Ans: The detergents which we use in our daily lives are-

· Clinic Plus, Dove etc. for washing hair

· soaps like Dettol, Dove, Lifeboy etc. for bathing

· detergents like Surf excel, Tide etc. for washing clothes

(g) What should be expected from a detergent for delicate garments ?

Ans: A delicate detergent should clean the clothes effectively without affecting the quality of the clothes. It should have the ability to remove all kinds of stains without causing any harm to the clothes.

(h) What is meant by ‘surface activity’ ? Name three chemicals responsible for the surface activity of various detergents.

Ans: Surface activity of a substance is the property by virtue of which it can spread on a surface. For example, soap water easily spreads on the any kind of surface and thus is used for cleaning purpose. Chemicals responsible for the surface activity of various detergents are alkylbenzene sulphonate, alcohol ethoxysulphates and alkyl sulphates.

3. What are the similarities and differences between -

(a) Natural detergents and man-made detergents

Ans:

Natural detergents	Man-made detergents
Natural detergents refer to the substances which are naturally available and can be used as detergents.	Man made detergents are detergents which have been made by humans for their use.
Examples of natural detergents include soap nut (ritha) and soap pod (shikhakai).	Example of man made detergent is soap.

(b) Soap and synthetic detergent

Ans:

Soap	Synthetic detergent
Soaps are sodium salt of fatty acids (soft soap) or potassium salts of fatty acids (hard soap).	Synthetic detergents are made up of raw materials like fats or kerosene.
They can be used only with soft water.	They can be used with both soft and hard water.

Ans:

Bath soap	Soap for washing clothes
It is a type of soft soap and used for bathing purposes.	It is a type of hard soap and is used for washing clothes.
Soft soaps are sodium salt of fatty acids.	Hard soaps are potassium salts of fatty acids.

(d) Modern cement and Ans:

Ans:

Modern cement	Ancient cement
It was developed by a British sceintist, John Smeaton.	It was developed by the Romans during the Roman empire.
It is made up of materials like lime (CaO), clay, silica along with some other oxides of aluminium, iron and magnesium and gypsum (CaSO4, 2H2O).	It was prepared by mixig volcanic ash in moistened lime.

4. Explain why -

(a) Soap cannot be used in hard water.

Ans: Soaps cannot be used in hard water because they lose their cleansing property when used with it. Soaps do not form lather with hard water and instead forms scum, as a result of which it loses its cleansing property.

(b) Oil does not mix in water. However, oil and water become homogeneous if a sufficient quantity of detergent is added.

Ans: Oil and water are two immiscible liquids which means both of them repel each other. But when we add a detegent to a solution conatining water and oil, the mixture becomes homogeneuos. This happens because of the detergent molecule. The detergent molecules have two ends. One of its end holds on to a water molecule and the other end holds on to the oil molecule. These opposing forces helps in dissolving the oil in water and thus making a homogeneous mixture.

Ans: Synthetic detergents are superior to soap because synthetic detergents work both in soft water and hard water. In contrast, soaps work only in soft water and they are not effective in hard water.

(d) Often coloured spots are formed on clothes during washing.

Ans: The laundry, skin care, beauty and personal hygiene products which we use commonly can cause stains and color changes in our clothes. Toothpaste, perspiration, facial soap, deodorants, hair sprays, strong perfumes with alcohol and even rain are often the cause of stains on garments. All these stains may eventually dry up not causing any visible stain however, age and exposure to heat will cause them to reappear.

(e) Tobacco masheri should not be used for cleaning teeth.

Ans: Tobacco has various kinds of negative effects on our body. It should not be used for cleaning teeths becuase it can harm th soft and hard tissues of our mouth. Use of tobacco poses serious risks like oral cancer, gum disease, poor healing after surgery, receding gums, and tooth decay.

7th Std Science 14 Elements, Compounds and Mixtures l Question and Answer

YADNYA e-Learning

Science Studies - 7th Standard

14. Elements, Compounds and Mixtures

Question And Answer

1. Who are my companions ?

2. Write the names of elements from the following symbols : Zn,

Cd, Xe, Br, Ti, Cu, Fe, Si, Ir, Pt.

Ans: Zn- Zink

Cd- Cadmium

Xe- Xenon

Br- Bromine

Ti- Titanium

Cu- Copper/Cuprus

Fe- Iron/ Ferrum

Si- Silicon

Ir- Iridium

Pt- Platinum

3. What are the molecular formulae of the following compounds ?

Ans: Hydrochloric acid- HCl

Sulphuric acid- H2SO4

Sodium chloride- NaCl

Glucose- C6H12O6

Methane- CH4

3. Give scientific reasons.

(a) Buttermilk is churned to get butter.

Ans: Churning is one of the method of separation. The

particles of butter are all spread out in the buttermilk. By

stirring they aggregate due to centrifugal force and form one

solid lump. To separate the butter, the buttermilk is

therefore churned.

(b) In chromatography, the ingredients of a mixture rise up to a

limited height when water rises up to the upper end of the paper.

Ans: In chromatography method two mutually opposite

properties of substances are used. These are:

1) The solubility of the substance in the solvent that moves

up.

2) The ability of the substance to stick to the stationary filter

paper. These properties are different for different substances.

Since water is a solvent, it rises rapidly across the

chromatography filter paper. But the solutes will not rise

with that speed. Therefore the ingredients of a mixture riseup to a limited height when water rises up to the upper end

of the paper.

summer.

Ans: A wet cloth is wrapped around water containers in

summers to keep the container and the water inside it cools.

The water present in the cloth evapourates and along with

that water the heat also evapourates thus keeping the

container and water cool.

5. Explain the difference.

(a) Metals and non-metals

Ans:

(b) Mixtures and compounds

Ans:

(d) Separation by distillation and by separating funnel

Ans:

6. Write answers to the following questions in your own words.

(a) How are the components of mixtures separated by simple

methods ?

Ans: There are various methods to separate the mixtures.

Some of these are used in our daily life such as straining,

shifting, picking, sorting, winnowing, combing with a magnet

and sublimation.

1) Straining- To separate insoluble substances from the

solution, we use the method of straining.

2) Shifting- Shifting is done to separate solids of various sizes.

The larger particles and the smaller particles can be

separated by shifting.

3) Picking and Sorting- By this method a substances that are

needed or do not needed are separated out.

4) Winnowing- The substances which are lighter in weight

and those that are unwanted are removed from the mixture.

The grains in the farm are particularly cleaned by the

process of winnowing.

5) Combing with a magnet- If there is adulteration of

semolina with iron, the magnet is combed through it for removing these iron particles. The mixture that contains iron

particles is specially combed with a magnet.

(b) Which elements (metals and non-metals), compounds and

mixtures do we use in our day-to-day life ?

Ans: Metals- Iron, Gold, Silver, Copper

Non-metals- Carbon, Oxygen, Hydrogen, Nitrogen

Compounds- Sugar, Salt, Oil

Mixtures- Soap, Alloy like steel, Brass, 22 Carat Gold

centrifugation?

Ans: Use of centrifuge machine is never done in our common

house-hold work. By using method of centrifugation the

particles of smaller size are separated due to centrifugal

force. Based on this principle, we use stirrer for making

buttermilk from yogurt. The stirrer helps to separate

particles of butter from the suspension of the buttermilk.

Due to centrifugal force, the particles of butter aggregate and

are thus easily removed.

(d) Where are the methods of separation by distillation and by

centrifugation ?

Ans: 1) Distillation- Distillation is the separation method

used to separate impurities or dissolved salts from the

solution. By this method, the solute and solvent are

separated. For removing salt from sea water, distillation

method is used. This helps in making portable water from

sea water.

2)Using separating funnel- When two liquids in a mixture

which are immiscible with each other are to be separated,

the method using separating funnel is used. This method can

be used separation of mixture of kerosene and water.

(e) Which precaution will you take while using the methods of

distillation and separation by separating funnel ?

Ans: In the method of distillation, the entire apparatus

should be properly set up. The distillation flask should be

carefully heated. The condenser tube should be properly

cooled. In the separating funnel experiment care should be

taken to well manipulate the stopcock. The malfunctioning

stopcock many a times releases the liquids inadvertently.

The separation of lower phase liquid should be done with

precision by opening and closing and stopcock.

7th Std Science 2 Plants : Structure and Function l Question and Answer

YADNYA e-Learning

Science Studies - 7th Standard

2. Plants : Structure and Function

1. Give examples of 3 plants that have :

(a) spiny fruits

Ans: Star Apple, Jackfruit, Castor, Sweet berries

(b) spiny stem

Ans: Cactus, Bamboo, Silk floss tree

Ans: Rose, Daisy, Marigold

(d) yellow flowers

Ans: Sunflower, Golden shower tree, Rose

(e) leaves which close at night

Ans: Mimosa, Gulmohar, Amla

(f) single-seeded fruits

Ans: Mango, Grapes, Date

(g) many-seeded fruits

Ans: Papaya, Jackfruit, Pomegranate

2. Observe any one flower and its various parts and describe it in your own words.

Ans: Various parts of flowers are described as follows:

1) Calyx : In the bud condition the petals are covered by leaf-like parts called sepals which are green in colour. They form the calyx.

2) Corolla : This is made up of colourful parts called petals. Its shape, colour and smell of the corolla of various flowers are different.

3) Androecium : This is the male reproductive part of the flower. It consists of stamens. Each stamen is made up of anther and filament.

4) Gynoecium : This is the female reproductive part of the flower. This is made up of carpels. A carpel consists of stigma, style and ovary.

3. What are the similarities and differences between?

(a) jowar and moong

Ans:

Similarities: Jowar and Moong both are angiosperms.

Difference Between:

Jowar	Moong
It has fibrous roots.	It has tap roots.
It is monocotyledonous seed.	It is dicotyledonous seed.

(b) onion and coriander

Ans:

Similarities: onion and coriander both are use for cooking

Difference Between:

onion	coriander
It has fibrous roots.	It has tap roots but
It is monocotyledonous seed.	It is dicotyledonous seed.

Ans:

Similarities: Leaves of banana and mango have medicinal use also

Difference Between:

leaves of banana	leaves of mango
It has parallel venation	It ha reticulated venation
It is large in size	It is small in size

(d) coconut tree and jowar stalk plant

Ans:

Similarities: coconut tree and jowar stalk plant both are auto trophic & both are monocotyledonous plant.

Difference Between:

coconut tree	jowar stalk plant
Coconut tree is tall	Jowar stalk plant is small
It has thick stem	It has thin stem

4. Explain the following images in your own words.

Ans:

Diagram A: In diagram A it is maize seed. It is a monocotyledonous seed. It does not divide into two equal parts. It has fibrous root system.

Diagram B: In diagram B it is bean seed. It is a dicotyledonous seed and it divide in to two equal parts. It has tap root system.

5. Describe the functions of various parts of a plant.

Ans: The roots, stem, leaves, flowers, fruits etc are different parts of plant. There functions are as follows:

Root: i) Anchoring and supporting the plant

ii) absorption of water and minerals

iii) Aerial roots absorb moisture from air, stilt roots give additional support, Runner roots help in vegetative propagation, Breathing roots are help to breath for plant, some underground roots store food materials etc.

Stem: i) To hold all the branches of the plant

ii) To perform function of photosynthesis as in cactus

iii) To transport water and food

iv) Stem perform functions such as food storage, reproduction, support etc.

Leaves: i) Production of food by performing photosynthesis

ii) Transpiration means giving out excess of water

iii) Leaves also perform functions like reproduction, food storage, support etc.

Flower: Reproduction

Fruits: Protection of seed and storage of food materials.

6. Certain properties are mentioned below. Find a leaf corresponding to each property and describe those plants.

leaves with smooth surface:

Ans: Banana leaf has smooth surface. It is large in size. It has parallel venation.

leaves with rough surface:

Ans:Hibiscus leaf has rough surface. It has reticulate venation. It is small in size.

fleshy leaf:

Ans: Water hyacinth has fleshy, glossy and smooth leaves. They are green in colour.

spines on leaf:

Ans: Opuntia is a desert plant Leaf is thick, fleshy and having spines on it. It is also called Prickly pear

7. Find the plant parts.