CLASSIFICATION OF SUBSTANCES Q/A

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Classification of Substances

EXERCISES
1. Write the answers to the following questions.
(a) How are properties of substances determined?
(b) Explain the differences between compounds and mixtures
(c) Why is an alloy a mixture?
(d) Why are substances classified?

2. Fill in the blanks.
(a) In a compound the ………………. do not retain their properties.
(b) In a …………… properties of constituents are retained.
(c) The chemical symbol of calcium is …………………… .
(d) The molecular formula for carbon dioxide is ……………………
(e) The compound sodium chloride is made from the combination of the elements ……….. and ………
(f) In the compounds H2O, NaOH and H2O2 ………….. are the common elements.

3. Given below are some compounds and the number of atoms of their constituent elements in each of their molecules. Write their molecular formulas.
Compound
Number of atoms of
constituent elements
formula
(a) Potassium hydroxide              
(b) Hydrogen peroxide
(c) Iron chloride
(d) Ammonium chloride
(e) Copper sulphate
(f) Magnesium oxide
K:1, O:1, H:1
H:2, O:2
Fe:1, Cl:2
N:1, H:4, Cl:1
Cu:1, S:1, O:4
Mg:1, O:1
KOH
…………………………
…………………………
…………………………
…………………………
…………………………


4. Match the following.
      Group ‘A’                            Group ‘B’
(a) Sodium                                 1. MgO
(b) Potassium                             2. FeS
(c) Iron sulphate                        3. Na
(d) Sugar                                   4. K
(e) Magnesium oxide                  5. C12H22O11
                                                 6. CO2 
ANSWERS
1. Write the answers to the following questions.
(a) How are properties of substances determined?
ANS:      1) The properties of substances are determined according to their atomic structure and atomic number.
                2) Example: Substances classified as elements, compounds, mixtures also as metals and non metals

(b) Explain the differences between compounds and mixtures
ANS:
Compounds
Mixtures
1. Compound is formed by combination
of two or more elements in fixed
proportion of weight
2. A new substance is formed when two
elements combine to form compound
3. Properties of compound are different
from its constituent elements
4. constituent elements are separated
using chemical processes
example:- H2O , CO2, MgO etc
1. A mixture is formed by mixing of
two or more substances in any proportion

2. A new substance is not formed in a
mixture
3. Constituent elements retain their
properties in a mixture.
4. constituent elements are separated
using physical processes.
Example:- steel, air, milk etc


(c) Why is an alloy a mixture?
ANS:      1) When two more substances are mixed together a mixture is formed. Alloy is a mixture of metals
                2) Proportion of constituents in the mixture is not fixed.
                3) In an alloy two or more elements are mixed together.
                4) When they are mixed their chemical properties are changed though there is no chemical reaction.
                5) Hence an alloy is a mixture. Example – Steel (alloy of iron and carbon), Brass(zinc and copper)

(d) Why are substances classified?
ANS:      1) Putting substances into groups based on their properties is called classification of substances.
                2) Due to classification, studying them becomes easier and convenient.
                3) Example: Substances classified as elements, compounds, mixtures also as metals and non metals

2. Fill in the blanks.
(a) In a compound the elements do not retain their properties.
(b) In a mixture properties of constituents are retained.
(c) The chemical symbol of calcium is Ca.
(d) The molecular formula for carbon dioxide is CO2
(e) The compound sodium chloride is made from the combination of the elements Sodium (Na) and Chloride (Cl).
(f) In the compounds H2O, NaOH and H2O2 hydrogen (H) are the common elements.

3. Given below are some compounds and the number of atoms of their constituent elements in each of their molecules. Write their molecular formulas.
Compound
Number of atoms of
constituent elements
formula
(a) Potassium hydroxide              
(b) Hydrogen peroxide
(c) Iron chloride
(d) Ammonium chloride
(e) Copper sulphate
(f) Magnesium oxide
K:1, O:1, H:1
H:2, O:2
Fe:1, Cl:2
N:1, H:4, Cl:1
Cu:1, S:1, O:4
Mg:1, O:1
KOH
H2O2
FeCl2
NH4Cl
CuSO4
MgO


4. Match the following.
                Group ‘A’                           Group ‘B’
(a) Sodium                                         3. Na
(b) Potassium                                     4. K
(c) Iron sulphate                                2. FeS
(d) Sugar                                           5. C12H22O11
(e) Magnesium oxide                             1. MgO

PROPAGATION OF SOUND Q/A

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 1. Answer the following
(a) Give a simple experiment to show that a medium is necessary for the propagation of sound.
(b) How is sound produced in drums?
(c) What is a noise?
2. Give reasons:
(a) A table player tightens or loosens the bands tying down the membrane.
(b) We hear thunder long after we have seen the flash of lightning.
(c) A surface is necessary for an echo to be heard.
3. Match the column
Group ‘A’                      Group ‘B’
(a) Reflection of sound                  1. The pegs on the sitar.
(b) Pollution of sound                    2. Water
(c) Medium of sound                     3. Echo point
(d) Frequency of sound                  4. Noise
4. Fill in the blanks
(a) A flautist can place figures on the proper holes and produce vibrations of the …………
(b) Sound is heard more clearly …………… as compared to air.
(c) In drums, …………….. vibrates to produce sound.
(d) The speed of light is …………………… times that of the sound.
(e) When temperature increases the speed of sound ……………….


1. Answer the following
(a) Give a simple experiment to show that a medium is necessary for the propagation of sound.
Ans:      Aim – To verify that a medium is necessary for the propagation of sound.
Requirements – 1) Take a round bottomed flask with some water in it and close it with a two holed rubber stopper. 2) Take a two holed rubber stopper and pass a glass rod or wire through one hole. 3)Tie a bell to one end of the rod and fit the stopper to the flask. 4) Pass a glass tube through another hole and attach a piece of rubber tubing fitted with a clamp to close it.
Experiment – 1) Open the clamp and heat the flask till water boils and steam comes out through the rubber tube. 2) Stop heating the flask and clamp the rubber tube shut. 3) Allow the flask to cool.
Observation – 1) The steam inside cools and condenses. 2) We cannot hear the ringing of the bell because after steam condenses, there is no medium left inside to carry the sound out of the flask. 3) When we open the clamp and allow outside air to enter inside, that air acts as medium and hence we hear the sound of the bell.
Figure – 
Conclusion – The medium is necessary for the propagation of sound.
(b) How is sound produced in drums?
Ans:
1)   A drum is a percussion instrument having a stretched membrane tied very tightly over it.
       2) The tension in the membrane can be varied.
3) When the membrane is struck, the tensed membrane starts vibrating which results in sound.
4) The desired frequency can be obtained by adjusting the tension in the membrane.

(c) What is a noise?
Ans:     
1) Noise is an unwanted sound
2) Noise follows no rules; frequencies change constantly, loudness changes irregularly.
       3) Nothing can be understood if there is noise.
       4) Noise pollution is a social problem.
       Example : Noise of traffic.

2. Give reasons:
(a) A tabla player tightens or loosens the bands tying down the membrane.
Ans:
1) A tabla is a percussion instrument having a stretched membrane tied very tightly over it.
       2) The tension in the membrane can be varied.
3) When the membrane is struck, the tensed membrane starts vibrating which results in sound.
4) The desired frequency can be obtained by adjusting the tension in the membrane.
5) Hence a tabla player tightens the bands tying down the membrane.

(b) We hear thunder long after we have seen the flash of lightning.
Ans:     
1) The speed of sound in air is about 340 metres per second (340 m/s)
       2) Light travels at about 3 x 108  m/sec.
3) That is, light travels at a speed which is about 106   times, or a million times, that of sound.
4) Therefore, though thunder and lightning occur at the same time, the flash of lighting travels faster than sound of thunder.
5) Hence we hear thunder long after we have seen the flash of lightning.

(c) A surface is necessary for an echo to be heard.
Ans:     
1) For an echo to be heard, the sound should be reflected back from some surface.
2) In an echo, the sound is reflected from a flat surface and travels back in the direction from which it came.
3) At echo points the echo is heard only after the sound is reflected from some opposite mountains.
4) Therefore a surface is necessary for an echo to be heard.


3. Match the column
Group ‘A’                    Group ‘B’
(a) Reflection of sound                  3. Echo point
(b) Pollution of sound                    4. Noise
(c) Medium of sound                     2. Water
(d) Frequency of sound                  1. The pegs on the sitar.

4. Fill in the blanks
(a) A flautist can place figures on the proper holes and produce vibrations of the air column.
(b) Sound is heard more clearly through water as compared to air.
(c) In drums, membrane vibrates to produce sound.
(d) The speed of light is 106 or a million times that of the sound.
(e) When temperature increases the speed of sound increases.



SOUND - PRODUCTION OF SOUND

08:35
SOUND - PRODUCTION OF SOUND
1. Write answers to the following questions.
(a) Why do we hear musical notes when strings of a sitar are plucked?
(b) How does a bat find its way in the dark?
(c) What is the SONAR system based on?
(d) Why is the sound of the bell smothered when a hand is placed on it?

2. Fill in the blanks.
(a) Man can hear sounds of sound frequencies between 20 and …………… Hz.
(b) Amplitude and …………….. are not related.
(c) The period of oscillation depends upon the ………………. Of the pendulum.

3. Match the following
                Group ‘A’                                            Group ‘B’
                (a) frequency                                    1. ultrasonic sound
                (b) period of oscillation                     2. metre
                (c) amplitude                                     3. second
                (d) bat                                              4. hertz
                                                                       5. audible sound

4. True or false?
(a) Frequency increases if amplitude is increased.
(b) A bat uses the principle of radar system while flying at night.
(c) Ultrasonic sounds are produced in the sonar system.
ANSWERS
1. Write answers to the following questions.
(a) Why do we hear musical notes when strings of a sitar are plucked?
ANS:      1) Vibration of source is necessary for the production of the sound.
                2) When we pluck the strings of a sitar, they vibrate and we hear characteristic sound.
                3) These characteristics sounds are different musical notes.
                4) Therefore we hear musical notes when strings of a sitar are plucked.

(b) How does a bat find its way in the dark?
ANS:      1) The bats produce ultrasonic sounds while flying in the dark.
                2) That sound is reflected from objects in front of the bat.
                3) From the reflected sound the bat comes to know of the position of things in its surroundings.
                4) Thus it is said that, with the help of ultrasonic sound a bat ‘sees’ with its ears to find its way in the dark.

(c) What is the SONAR system based on?
ANS:      1) Sonar system is based on the ultrasonic sound.
                2) Sonar is a kind of radar system
                3) Ultrasonic sounds are produced and caused to be reflected.
                4) The radar system tells the position of the objects by getting the waves it produces reflected from targets in front.
                5) Sonar system is used to detect impurities inside the metal, also to measure the depth of the ocean floor etc

(d) Why is the sound of the bell smothered when a hand is placed on it?
ANS:      1) Vibration of source is necessary for the production of the sound.
                2) The sound of the bell is produced because vibrations of the bell.
                3) If we place our over the vibrating bell, the vibrations are interrupted.
                4) Therefore, the sound of the bell smothered when a hand is placed on it

2. Fill in the blanks.
(a) Man can hear sounds of sound frequencies between 20 and 20,000 Hz.
(b) Amplitude and frequency are not related.
(c) The period of oscillation depends upon the length of the pendulum.

3. Match the following
                Group ‘A’                                            Group ‘B’
                (a) frequency                                    4. hertz
                (b) period of oscillation                      3. second
                (c) amplitude                                     2. metre
                (d) bat                                              1. ultrasonic sound

4. True or false?
(a) Frequency increases if amplitude is increased.
Ans: False [Even if frequency is increased amplitude remains the same]
(b) A bat uses the principle of radar system while flying at night.
Ans: False [A bat uses ultrasonic sounds while flying at the night]
(c) Ultrasonic sounds are produced in the sonar system.
Ans: True




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