Allied solutions simplified middle school chemistry class 8 Solutions for Chapter 7 hydrogen

Q1) State how hydrogen occurs in the free state. Name three compounds containing hydrogen in the combined state.

Q2) Starting from zinc how would you obtain hydrogen using

(a)Steam

(b) A dilute acid

(c) An alkali

( Give balanced equations for each and name the product formed in each case other than hydrogen) Name a metal which will not react with the reactants above to give hydrogen.

Q3) 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 .

Q4) In the laboratory preparation of hydrogen from zinc & dilute hydrochloric 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.

Q5)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 promoter to the catalyst in the final step

(c) The name of the solution which absorbs the unreacted carbon monoxide.

Q6) State the following pertaining to the physical properties of hydrogen

(a) Colour & odour

(b) Solubility in water

(c) Effect on moist blue litmus paper

Q7) Draw neat labelled diagrams for two experiments to prove that hydrogen is lighter than air.

Q8)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

Q9)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.

Q10) State a reason why, when hydrogen is passed over heated copper oxide, the resultant product formed, differs in colour from the original reactant.

Q11) 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.

Q12) Give a test to differentiate between two gas jars - one containing pure hydrogen and the other hydrogen - air mixture.

Q13)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 - _____ of oxygen to a substance or ____ of hydrogen from a substance. Reduction on the other hand involves ____ of hydrogen to a substance or _____ of oxygen from a substance’.

Q14) With reference to the equation: Cl_2+H_2S→2HCl+S pertaining to a redox reaction - select the correct answer in each case -

(a) Chlorine is oxidised/reduced to HCl

(b) Hydrogen sulphide is oxidised/reduced to sulphur since the reaction involves addition/removal of hydrogen.

(c) Chlorine acts as an oxidising/reducing agent.

Q1) 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.

Q2) 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.

Q3) 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.

Q4) Select the correct answer from the choice in the bracket to complete each sentence.

1. The acid _______ [ dilute H_2SO_4, dilute HNO_3, dilute 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_2,\ CO,\ C ]

3. A foul smelling gas formed when hydrogen reacts with a molten non-metal, is ________ [[Hydrogen chloride, hydrogen sulphide, ammonia]]

4. The product formed on combustion of hydrogen in air is _______ [[ water gas, water, producer gas ]].

5. The gas which has now replaced hydrogen in air balloons is _______ [[ argon, helium, neon ]]

Q5) Match the statements in List I with the appropriate answer in List II