Z1xyw 5 Answer Key

[Melissa Alvarado]

Question5.

Sodium hydroxide is termed an alkali, while Ferric hydroxide is not because:

(a) Sodium hydroxide is a strong base, while Ferric hydroxide is a weak base.

(b) Sodium hydroxide is a base which is soluble in water while Ferric hydroxide is also a base but it is not soluble in water.

(c) Sodium hydroxide is a strong base while Ferric hydroxide is a strong acid.

(d) Sodium hydroxide and Ferric hydroxide both are strong base but the solubility of Sodium hydroxide in water is comparatively higher-than that of Ferric hydroxide.

Answer:

(b) Sodium hydroxide is a base which is soluble in water while Ferric hydroxide is also a base but it is not soluble in water.

(iv) Tubular part of nephron. When the filtrate containing useful substances as well as the waste substances passes through the tubule, then the useful substances like glucose, all amino acids, most salts and most water etc. are reabsorbed into the blood through blood capillaries surrounding the tubule. Only the waste substances urea, some unwanted salts and excess water remain behind in the tubule in the form of urine.

Question 24.

Two green plants are kept separately in oxygen free containers, one in the dark and other in sunlight. It was observed that plant kept in dark could not survive longer. Give reason for this observation.

Answer:

The plant which is kept in oxygen-free container in continuous sunlight will live longer because it will be able to produce oxygen required for its cellular respiration by the process of photosynthesis.

The plant which is also kept in oxygen-free container, but in the dark will not photo- synthesize and hence it will finally die due to non-availability of oxygen for its respiration.

Question 25.

(a) Observe the following diagram and answer the questions following it:

(i) Identify the defect of vision shown.

(ii) List its two causes.

(iii) Name the type of lens used for the correction of this defect.

OR

(b) The colour of clear sky from the earth appears blue but from the space it appears black. Why?

Answer:

(a) (i) Defect of vision shown is Myopia.

(ii) Causes:

1. Due to the elongation of the eye ball.

2. Due to decrease in the focal length of the eye lens and hence the eye lens becomes more convergent.

(iii) Concave lens of suitable focal length is used for the correction of Myopia.

OR

(b) Sky appears blue. The molecules of air and other fine particles in the atmosphere have a size smaller than the wavelength of visible light. So these particles scatter more effectively the light rays of shorter wavelength at the blue end than light of longer wavelengths at the red end. When the scattered blue light enters our eyes, it gives us the feeling of a blue sky.

Colour of Sky to an Astronaut. There is no atmosphere containing air in space to scatter sunlight. As there is no scattering of light in space, the scattered light does not reach the eyes and the sky appears dark (black) instead of blue to An astronaut in the outer space.

Question 26.

Use of several pesticides which results in excessive accumulation of pesticides in rivers or ponds, is a matter of deep concern. Justify this statement.

Answer:

At present time, water pollution by pesticides is a critical issue, especially in range of extensive agriculture where leaching of these harmful chemicals in water bodies like rivers or ponds cause toxic effects on aquatic animals and human health. The toxic substances may run off into streams and ground water. It may cause the death of aquatic animals. Some harmful chemicals like pesticides, when absorbed by the plants through soil and water, get transferred from first trophic to the last trophic level of the food chain.

As these chemicals are non-degradable, their concentration in the bodies of living organisms at each trophic level progressively increases. This increase in the concentration of harmful chemicals in the body of living organisms at each trophic level of a food chain is called biological magnification. The level of concentration of chemicals is maximum for human beings as they are at the highest trophic level.

Question 27.

(i) While electrolysing water before passing the current some drops of an acid are added. Why? Name the gases liberated at cathode and anode. Write the relationship between the volume of gas collected at anode and the volume of gas collected at cathode.

(ii) What is observed when silver chloride is exposed to sunlight? Give the type of reaction involved.

Answer:

(a) (i) While electrolysing water before passing the current some drops of an acid are added to make water a good conductor of electricity.

Hydrogen gas (H2) is liberated at cathode and Oxygen gas (O2) is liberated at anode. The ratio of volume of O2 (gas collected at anode) and the volume of H2 (gas collected at cathode) is 1 : 2 by volume.

Question 28.

(i) Suggest a safe procedure of diluting,a strong concentrated acid.

(ii) Name the salt formed when sulphuric acid is added to sodium hydroxide and write its pH.

(iii) Dry HCl gas does not change the colour of dry blue litmus paper. Why?

Answer:

(i) The dilution of a concentrated acid should always be done by adding concentrated acid to water gradually with stirring and not by adding water to concentrated acid because when a concentrated acid is added to water for preparing a dilute acid, then the heat is evolved gradually, and easily absorbed by the large amount of water.

Question 29.

(a) (i) How does Paramecium obtain its food?

(ii) List the role of each of the following in our digestive system:

(a) Hydrochloric acid

(b) Trypsin

(c) Muscular walls of stomach

(d) Salivary amylase

OR

(b) (i) What is double circulation?

(ii) Why is the separation of the right side and the left side of the heart useful? How does it help birds and mammals?

Answer:

(a) (i) Paramecium is a unicellular organism which lives in water. Paramecium uses its hair like structures called cilia to sweep the food particles from water and put them into its mouth.

(ii) Systemic circulation. The pathway of the blood from the heart to the : rest of the body and back to the heart is called systemic circulation. It is a large circulation. Left ventricle sends the blood into the aorta. Aorta divides into arteries, arterioles and capillaries and supplies oxygenated blood to various parts of the body. From there the deoxygenated blood is collected by venules, which join to form veins and finally vena cava and pours blood back into the right atrium.

(ii) (a) Humans have a four chambered heart which consists of two atria and two ventricles. In a four chambered heart, the left side and right side of the heart are completely separated to prevent the oxygenated blood from mixing with deoxygenated blood. Such a separation allows a highly efficient supply of oxygen to the body cells which is necessary for producing a lot of energy. This energy is useful for a warm blooded animal (like humans) which has high energy needs to maintain body temperature.

Question 32.

(a) (i) Why is an alternating current (AC) considered to be advantageous over direct current (DC) for the long distance transmission of electric power?

(ii) How is the type of current used in household supply different from the one given by a battery of dry cells?

(iii) How does an electric fuse prevent the electric circuit and the appliances from a possible damage due to short circuiting or overloading.

OR

(b) For the current carrying solenoid as shown, draw magnetic field lines and give reason to explain that out of the three points A, B and C, at which point the field strength is . maximum and at which point it is minimum?

Answer:

(a) (i) Alternating Current (AC) is considered to be advantageous over Direct Current (DC) because Alternating Current (AC) can be transmitted over long distances without much loss of electrical energy.

(ii) The current used in household supply is Alternating Current (AC) whereas the current given by a battery of dry cells is Direct Current (DC).

(iii) Overloading or short circuiting can be highly damaging to electrical appliances and buildings. So, fuse of proper rating must be used to avoid such damage. A fuse-wire will melt before the temperature of the heated circuit wire becomes too high and causes the circuit to break.

OR

(b) The magnetic field produced is directly proportional to the current passing in the wire and inversely proportional to the distance of the point from the current carrying conductor. Therefore as the distance of a point from the current carrying conductor increases, the strength of

the magnetic field becomes weaker. Out of the three given points A, B and C, Point A has the maximum magnetic field strength as it is at minimum distance from the current carrying conductor. Point C has the minimum magnetic field strength as it is at maximum distance from the current carrying conductor.

Question 33.

Write one difference between biodegradable and non-biodegradable wastes. List two impacts of each type of the accumulated waste on environment if not disposed off properly.

Answer:

Impact of biodegradable waste on the environment:

1. Biodegradable wastes are decomposed by the action of micro-organisms and may produce foul smell during the decomposition process.

2. Waste decomposition in landfills produces harmful methane gas which is a green house gas (100 to 120 times more powerful than CO2) that contributes to Global warming.

Impact of non-biodegradable waste on the environment:

1. Non-biodegradable waste does not decompose. These accumulate in the environment and cause biomagnification. As a result of this accumulation, they pollute soil and water.

2. Non-biodegradable wastes such as pesticides deplete soil fertility and so reduce the crop yield.

3. If these wastes are burnt, it causes air pollution.

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