- Raman Ayan
- Mar 1, 2024
- 1 min read
Updated: Mar 2, 2024
Short Notes
Very Short Notes
Identify the error in the given statements. Circle the incorrect word and write the correct word in the blank.
Give Reasons
Answer the following Questions
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- Raman Ayan
- Feb 26, 2024
- 3 min read
Updated: Feb 28, 2024
Class 6
Fill in the Blanks
edit ________________ (Rainwater/Surface water) is the purest form of water. Answer : Rainwater
edit The density of water is maximum at ________________. Answer : 4°C
edit ________________ is the amount of heat energy required to raise the temperature of a liquid by 1°C. Answer : Specific heat capacity
edit Large amount of water is also given out by the leaves of plants during ________________. Answer : transpiration
edit Water helps in the excretion of waste from the body in the form of ________________, urine or while breathing. Answer : sweat
edit Water is very important for ________________ of seeds. Answer : germination
edit About ________________ of the fresh water is present in rivers, lakes, springs, ponds, etc. Answer : one-third
edit In ________________ state, water exists as snow or frost. Answer : solid
edit Water exists as ________________ or ________________ in gaseous state. Answer : water vapour, steam
edit The density of water is ________________ at 4 degree Celsius. Answer : maximum
edit Water regulates the body ________________ of plants and animals. Answer : temperature
edit Water acts as a ________________ in powerhouses which generate electricity. Answer : coolant
edit Solubility of a solute ________________ on increasing the temperature. Answer : increases
edit A solution is said to be ________________ when it can dissolve more of the solute at a particular temperature. Answer : unsaturated
edit ________________ is an infection in the small intestine caused by a bacterium. Answer : Cholera
edit The addition of unwanted and harmful substances to water is called ________________. Answer : water pollution
Fill in the blanks with anxwers
(a) Water is a universal; solvent.
(b) Rainwater is the purest form of natural water.
(c) Sand and dust are suspended impurities in water.
(d) Sea water has high concentration of salt (impurity).
(e) Water covers nearly 4 / 5 th of the surface of the earth.
(f) Evaporation of rain water leaves NO residue.
(g) Potash alum is the chemical added to water to remove the tiny suspended particles.
(h) A solution is a uniform mixture of a solute and a solvent.
(i) Ice, water and steam have different physical states but are chemically identical.
(j) Boiling kills most of the germs in water.
(k) The elements present in the molecules of water are hydrogen and oxygen.
1. Water is essential for running .......................... power plants.1 |
2. A sample of water which is fit for human .......................... is called potable water. |
3. A solution which cannot dissolve more of solute is called ............................. solution. |
4. Distilled water is ...................................... water. |
5. Fish die in ................................. ponds during summer season |
Answers
Fill in the blanks 1. hydroelectric |
2. consumption |
3. saturated |
4. pure |
5. shallow |
Class 8
1. Fill in the blanks:
(a) Water has maximum density and minimum volume at 4°C.
(b) Freezing mixture contains ice and salt.
(c) The solubility of a gas in water increases with rise in temperature and decreases with rise in pressure.
(d) Rain water is the purest form of natural water.
(e) Use of excessive fertilizers by farmers causes water pollution.
(f) Boiling removes the temporary hardness of water.
(g) Water turns the colour of anhydrous copper sulphate blue.
(h) Water turns the colour of anhydrous copper sulphate scum.
Class 9
Fill in the blanks:
Water forms about ________ of human body and almost ________ of some plants.
________ is used for drinking purpose.
A solution of iodine in alcohol known as ________.
Anhydrous substance lack their ________.
Concentrated ________ remove water of molecules from blue vitriol. It is a ________ agent.
Washing soda contains ________ molecules of water of crystallisation.
The higher the temperature of the air, the ________ the efflorescence.
Land and sea breeze are caused by ________ property of water. [specific heat capacity/latent heat of vaporisation]
________ gas is more soluble in water. [nitrogen/oxygen]
Air is the example of ________ solution.
The boiling point of water ________ due to the presence of dissolved impurities. [increases/decreases]
Water molecule has _______ bonding in it. [ionic, covalent]
(i) 65%, 95% (ii) Soft water (iii) tincture of iodine (iv) water of crystalisation (v) sulphuric acid, dehydrating (vi) ten (vii) higher (viii) specific heat capacity (ix) oxygen (x) gaseous (xi) increases (xii) covalent
A.L. Lavoisier, in the year (i) ________ showed that water is a compound of (ii) ________ and (iii) ________ atoms combined together in the ratio of (iv) ________.
Answers ;
(i) 1781, (ii) hydrogen, (iii) oxygen, (iv) 2 : 1
- Raman Ayan
- Feb 19, 2024
- 7 min read
Updated: Feb 21, 2024
Question: 1. State how hydrogen occurs in the free state. Name three compounds containing hydrogen in the combined state.
Answer: In Free state:
In traces : Hydrogen occurs in minute traces in the earth’s crust, atmosphere & in volcanic gases
In & around the sun : Hydrogen occurs in the interior of the sun which consists mainly of hydrogen, which is converted to energy released as heat & light.
The compounds containing hydrogen are: ammonia (NH3), hydrochloric acid (HCl), water(H2O)
Question: 2. Starting from zinc how would you obtain hydrogen using-
(a) Steam(b) A dilute acid(c) An alkali
[Give balanced equations for each & name the product formed in each case other than hydrogen]. Name a metal which will not react with the reactants above to give hydrogen.
Answer: (a) Steam : Zn reacts with steam to form zinc oxide and liberate hydrogen gas.
Zn + H2O ⟶ ZnO + H2 ↑
Lead (Pb) will not react with steam to give hydrogen.
(b) A dilute acid : Zn reacts with dil. sulphuric acid to form zinc sulphate and liberate hydrogen gas.
Zn + H2SO4 ⟶ ZnSO4 + H2 ↑
Copper (Cu) will not react with dilute acid to give hydrogen.
(c) An alkali : Zn reacts with sodium hydroxide to form sodium zincate and liberate hydrogen gas.
Zn + 2NaOH ⟶ Na2ZnO2 + H2 ↑
Silver (Hg) will not react with alkali to give hydrogen.
Question: 3. ‘Hydrogen is obtained by electrolysis of acidified water’. Answer the following pertaining to the preparation of hydrogen by electrolysis,
(a) The meaning of the term ‘electrolysis’ and ‘electrolyte’,
(b) Name the electrode –
1. through which the current enters the electrolyte.
2. at which hydrogen is liberated.
Answer: (a) Electrolysis — It is the process of decomposition of a chemical compound [electrolyte] in the fused [molten] or solution state by passage of an electric current resulting in the dissociation of the chemical compound into ions which are discharged as neutral atoms at the respective electrodes.
Electrolyte — A chemical compound which in the molten or solution state can conduct electric current & undergo chemical decomposition due to flow of current.
(b) The electrodes are:
1. Anode
2. Cathode
Question: 4. In the laboratory preparation of hydrogen from zinc & dilute hydro choloric acid – state a reason for
(a) Addition of traces of copper [II] sulphate to the reaction medium(b) Collecting the hydrogen by downward displacement of water and not air & collecting it after all the air in the apparatus is allowed to escape(c) Having the end of the thistle funnel dip below the level of the acid in the flask.
Answer: (a) Addition of traces of copper [II] sulphate to the reaction medium enhances the speed of the reaction.
(b) Hydrogen forms a highly explosive mixture with air. Hence, it is not collected by the downward displacement of air and collected only after all the air in the apparatus is allowed to escape. As it is almost insoluble in water, so it is collected by downward displacement of water.
(c) The lower end of the thistle funnel should dip below the level of the acid in the flask, otherwise hydrogen gas produced will escape through thistle funnel.
Question: 5. In the industrial method of preparation of hydrogen by the Bosch process – give
(a) Balanced equations for the first two main steps in the production of hydrogen(b) The reason for use of addition of a promoter to the catalyst in the final step(c) The name of the solution which absorbs the unreacted carbon monoxide.
Answer: (a) Balanced equations for first two main steps of Bosch process:
Step I — Production of water gas
Step II — Reduction of steam to hydrogen by carbon monoxide
(b) Promoter increases the efficiency of the catalyst.
(c) Ammoniacal cuprous chloride solution [CuCl].
Question: 6. State the following pertaining to the physical properties of hydrogen :
(a) Colour & odour(b) Solubility in water(c) Effect on moist blue litmus paper.
Answer:
(a) Colour & odour — colourless and odourless
(b) Solubility in water — Very slightly soluble in water
(c) Effect on moist blue litmus paper — neutral to litmus
Question: 7. Draw neat labelled diagrams for two different experiments to prove that – hydrogen is lighter than air.
Answer: Hydrogen is lighter than air:
To show that H2 is lighter than air :
Air from jar B being heavier runs down in jar A and H2 runs to jar B as it is lighter than air and burns with ‘pop’ sound in jar B if a burning splinter is brought there. Question: 8. Starting from hydrogen gas how would you obtain
(a) A neutral liquid(b) A basic gas(c) A metal by reduction of its heated oxide.
[The metal formed is above iron in the activity series]
Answer:(a) Hydrogen burns quietly in oxygen with a pale blue flame and water is formed.
2H2 + O2 ⟶ 2H2O
(b) Three volumes of hydrogen, reacts with one volume of nitrogen to form ammonia which is a basic gas.
(c) Hydrogen reduces oxides of less active metals e.g. zinc to form the reduced metal & water.
ZnO + H2 ⟶ Zn + H2O
Question: 9. Using a burning candle and a jar of hydrogen – how would you prove experimentally that (a) Hydrogen is a combustible gas (b) Hydrogen does not support combustion.
Answer: Experiment : Take a jar filled with hydrogen with inverted mouth downwards and introduce a burning candle near the mouth of jar.
Observation : The gas burns at the mouth of the jar while the burning candle is extinguished when pushed inside the jar.
Conclusion :
Hydrogen is combustible & hence burns at the mouth of the jar.
It does not support combustion and extinguishes a burning candle when pushed inside
Question: 10. State a reason why, when hydrogen is passed over heated copper oxide, the resultant product formed, differs in colour from the original reactant.
Answer: As hydrogen is a strong reducing agent hence it reduces heated copper (II) oxide to copper. Therefore, the original black copper (II) oxide changes to reddish brown copper.
Question: 11. With reference to the uses of hydrogen, give reasons for the following :
(a) Hydrogen is not used in air balloons(b) A mixture of hydrogen & oxygen on burning, find application in welding & cutting metals(c) Reaction of hydrogen with nitrogen under specific conditions finds industrial utility.
Answer: (a) Hydrogen is lighter than air but it is a highly combustible gas. It forms an explosive mixture with air (due to the oxygen present in it). Hence, it is not used in air balloons.
(b) A mixture of hydrogen & oxygen on burning produces heat [temperatures upto 2800°C]. Such high temperature flames are used for welding & cutting metals.
(c) Hydrogen combines with nitrogen at 450°C and in the presence of catalyst iron to give ammonia. Ammonia is used in the manufacture of urea, fertilizers, nitric acid, explosives, etc.
Question: 12. Give a test to differentiate between two gas jars – one containing pure hydrogen and the other hydrogen-air mixture.
Answer: When a burning splinter is brought near the mouth of the gas jar containing pure hydrogen, it burns quietly with a pale blue flame whereas the other jar containing hydrogen-air mixture burns with a pop sound.
Question: 13. With reference to oxidation & reduction reaction – complete the statement given by filling in the blanks with only the words (a) Addition (b) Removal.
‘Oxidation is a chemical reaction involving addition of oxygen to a substance or removal of hydrogen from a substance. Reduction on the other hand involves addition of hydrogen to a substance or removal of oxygen from a substance.
Question: 14. With reference to the equation :
Cl2 + H2S → 2HCl + S
pertaining to a redox reaction – select the correct answer in each case –
(a) Chlorine is reduced (oxidised/reduced) to HCl.(b) Hydrogen sulphide is oxidised (oxidised/reduced) to sulphur since the reaction involves removal (addition/removal) of hydrogen.(c) Chlorine acts as an oxidising (oxidising/reducing) agent.
MCQ
Question: 1. Give balanced equations for the following conversions :
1. Zinc to sodium zincate – using an alkali.
2. Acidic water to hydrogen – by electrolysis.
3. Water gas to hydrogen – industrially
4. Iron [[III]] oxide to iron – using hydrogen.
5. Nitrogen to a basic gas – using hydrogen.
Answer: 1. Zn + 2NaOH ⟶ Na2ZnO2 + H2 ↑
2. 2H2O ⇌ 2H2 + O2
4. Fe2O3 + 3H2 ⟶ 2Fe + 3H2O
5. N2 + 3H2 ⇌ 2NH3
Question: 2. Give reasons for the following :
1. Copper does not displace hydrogen from dilute hydrochloric acid, but zinc does.
2. In the preparation of hydrogen by electrolysis of water – the distilled water used is acidified.
3. In the laboratory preparation of hydrogen from zinc and dilute hydrochloric acid – the zinc used granulated zinc.
4. In the Bosch process – the final gaseous products are passed through caustic potash [[KOH]] solution.
5. The reaction of chlorine with hydrogen sulphide is deemed a redox reaction.
Answer:
1. In the metal reactivity series, copper (Cu) is below hydrogen but zinc (Zn) is above hydrogen. Hence, copper does not displace hydrogen from dilute hydrochloric acid, but zinc does.
2. Pure water is almost a non-electrolyte and will not normally conduct electricity. It consists almost entirely of molecules. It can be electrolytically decomposed by addition of traces of dil. H2SO4 which dissociates as: H+1 and SO4-2 and help in dissociating water into H+ and OH– ions.
3. Granulated zinc contains traces of impurities, which has a slight catalyzing effect on the reaction and speeds it up.
4. CO2 is removed by dissolving mixture in caustic potash solution.
2KOH + CO2 ⟶ K2CO3 + H2O
5. Hydrogen sulphide reacts with chlorine as per the below equation:
H2S + Cl2 ⟶ 2HCl + SHere, H2S is oxidised to S and Cl2 is reduced to HCl, at the same time. Hence, it is a redox reaction.
Question: 3. Select the correct answer from A, B, C, D or E for each statement given below :
A: Nickel B: Sodium C: Iron D: Iron [III] oxide E: Magnesium oxide
1. A metal which reacts with water to give a metallic hydroxide & liberate hydrogen.
2. The metallic compound used as a catalyst in the Bosch process.
3. The metal used as a catalyst in hydrogenation of oils.
4. The metal which reacts with steam liberating hydrogen & the reaction is reversible.
5. The metallic compound formed when a metal above aluminium in the activity series reacts with steam.
Answer:
1. A metal which reacts with water to give a metallic hydroxide & liberate hydrogen. | B: Sodium |
2. The metallic compound used as a catalyst in the Bosch process. | D: Iron [III] oxide |
3. The metal used as a catalyst in hydrogenation of oils. | Chemistry |
4. The metal which reacts with steam liberating hydrogen & the reaction is reversible. | Dalal New Simplified |
5. The metallic compound formed when a metal above aluminium in the activity series reacts with steam. | Hydrogen |
Question: 4. Select the correct answer from the choice in bracket to complete each sentence.
1. The acid …dil.HNO3… [dil.H2SO4 , dil.HNO3, dil.HCl] is not used in the laboratory preparation of hydrogen, using zinc and an acid.
2. In Bosch process the catalytic reduction of steam to hydrogen is carried out by …CO… [CO2 , CO, C].
3. A foul smelling gas formed when hydrogen reacts with a molten non-metal, is …hydrogen sulphide… [hydrogen chloride, hydrogen sulphide, ammonia].
4. The product formed on combustion of hydrogen in air is …water… [water gas, water, producer gas].
5. The gas which has now replaced hydrogen in air balloons is …helium… [argon, helium, neon].
Question: 5. Match the statements in List I with the appropriate answer in List II.
List I | List II |
1. An atom of hydrogen | A: Chromic oxide |
2. A strong oxidising agent | B: Ammonia |
3. A promoter used in Bosch process | C: Iron |
4. A chemical used in the manufacture of fertilizers | D: One electron |
5. The catalyst used in production of a basic gas from nitrogen | E: Dilute nitric acid |
Answer:
List I | List II |
1. An atom of hydrogen | A: One electron |
2. A strong oxidising agent | B: Dilute nitric acid |
3. A promoter used in Bosch process | C: Chromic oxide |
4. A chemical used in the manufacture of fertilizers | D: Ammonia |
5. The catalyst used in production of a basic gas from nitrogen | E: Iron |
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