Gases & Metal and Non-Metal
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Lesson – 16.
Gases.
Exercise.
2) Give reason.
(a) Carbon dioxide can be collected in an open glass jar.
Answer: Because, carbon dioxide is heavier than air so it stays at the bottom of glass jar.
(b) The bottle of liquid ammonia should be placed in cold water or ice for some time before opening its lid.
Answer: Because when placed in cold water or ice for some time the molecules of ammonia gets contracted. If not done while opening the lid the liquid ammonia will come out of the bottle at a high pressure and gets poured in our mouth, eye or in clothes.
3) Answer the following questions.
(a) Describe the laboratory preparation of carbon dioxide with labelled diagram.
fig: Lab preparation of carbon dioxide.
procedure:
- collect all the required apparatus and chemicals for this gas.
- keep pieces of limestone or marble pieces in woulf’s bottle.
- Connect all the apparatus as shown in the figure by making everything
air tight.
- pour dilute HCl through thistle funnel into woulf’s bottle till it covers the limestone or marble.
- Allow the gas pass through the delivery tube.
- HCl + limestone reacts with dilute HCl and effervescence of CO2 gas can be seen which is collected in the gas jar by upward displacement of air.
(b) study the given figure and answer the following questions:
(i) Which gas is being collected into the gas jar?
Answer: Carbon dioxide (CO2)
(ii) Write a balanced chemical reaction for preparation of this gas.
(iii) Which litmus paper is used to identify the gas?
Answer: moist blue litmus paper.
(iv) Why is this gas collected in the gas jar kept straight upright?
Answer: Because, CO2 is heavier than air, so it can be collected by upward displacement of air.
(c) Write 3 properties of carbon dioxide gas.
Answer: Three properties of carbon dioxide gas are:
- It is 1.5 times heavier than air.
- Slightly soluble in water.
- neither combustible nor is supporter of combustion.
(d) Write any four uses of carbon dioxide gas.
Answer: Following are the four uses of carbon dioxide gas:
- used for the preparation of carbonated drinks.
- Used to prepare Urea (NH2CONH2), washing soda (Na2CO3) and baking soda (NaHCO3).
- Used in bakery products.
- green plants use carbon dioxide for photosynthesis.
- Used to prepare dry ice – used as coolant.
(e) Describe the laboratory preparation of ammonia gas with a labelled diagram.
fig: Lab preparation of ammonia.
Procedure:
- collect all the apparatus and chemicals required for the laboratory preparation of ammonia gas.
- Take a mixture of ammonium chloride and slaked lime (Ca(OH)2) in the ratio of 2:1 in a round bottomed flask.
- Add a little water for making a paste.
- connect all the apparatus as shown in the figure making air tight.
- Gently heat the mixture to generate ammonia gas.
- Lime tower filled with calcium oxide (CaO) is used to obtain dry and pure ammonia. This gas is quite soluble in water so it is not obtained by displacement of water. It is collected by the downward displacement of air as it is lighter than air.
(f) Study the given figure and answer the following questions.
(i) Which gas is being collected in the gas jar?
Answer: Ammonia gas (NH3).
(ii) Write the balanced chemical equation for the preparation of this gas.
(iii) Which litmus paper is used to identify this gas?
Answer: moist red litmus paper.
(iv) Why the hard glass test tube is slightly inclined?
Answer: To pass the gas properly the hard glass test-tube is slightly inclined.
(v) What is the use of lime tower?
Answer: The use of lime is to absorb all the moisture or water and form pure ammonia gas.
(g) Write any four uses of ammonia gas.
Answer: It’s four uses are:
- Liquid ammonia is used as refrigerant.
- Used in blue printing of maps.
- used to make fertilizers.
- Used as reagent in laboratories.
(h) What happens in the following processes. Write with a balanced chemical reaction.
(i) Carbon dioxide is passed through lime water for some time.
The lime water turns milky white due to the formation of insoluble calcium carbonate.
(ii) Carbon dioxide is passed through lime water for long time.
The milky white colour disappears due to the formation of soluble calcium bicarbonate.
(iii) A burning magnesium is inserted into the jar full of carbon dioxide gas.
It burns brightly and produces white powder of magnesium oxide (MgO) and black carbon powder.
(iv) The mixture of ammonium chloride and calcium hydroxide is heated.
Ammonia gas will be formed.
(v) Ammonia is mixed with water.
It forms ammonium hydroxide.
(vi) Ammonia reacts with hydrochloric acid.
It forms Ammonium chloride.
(iii) A burning magnesium is inserted into the jar full of carbon dioxide gas.
It burns brightly and produces white powder of magnesium oxide (MgO) and black carbon powder.
(iv) The mixture of ammonium chloride and calcium hydroxide is heated.
Ammonia gas will be formed.
(v) Ammonia is mixed with water.
It forms ammonium hydroxide.
(vi) Ammonia reacts with hydrochloric acid.
It forms Ammonium chloride.
Unit 17.
Metal and Non-metal.
Exercise.
2) Give reason:
(a) All ores are minerals but all minerals are not ores.
Answer: All ore are mineral because it’s natural occuring and has a definite composition. But not all minerals are ores because many minerals don’t have enough metal to extract profitably.
(b) Ores are oxidised after concentration.
Answer: Ores are oxidised after concentration because it is easier to extract metals from their oxides.
3) Difference between.
(a) Minerals and Ores
| Minerals | Ores |
|---|---|
| The elements and compounds which are found naturally are called minerals. | The minerals from which metals are extracted are called ores. |
| They are obtained from earth’s crust. | ores are obtained from minerals. |
(b) Roasting and Calcination
| Roasting | Calcination |
|---|---|
| The process of strongly heating the ores to their oxides by passing air or in presence of oxygen is called roasting. | The process of strongly heating the ore to their oxides in the absence of air or without passing oxygen is called calcination. |
| Roasting is done to convert sulphide ores to their oxide ores. | calcination is done to convert carbonate ores to their oxides. |
(c) Oxidation and Reduction
| Oxidation | Reduction |
|---|---|
| It is a process of changing concentration ores to metal ores. | It is the process of removing oxygen from their metal. |
| There are two process of oxidation. | There is only one process for reduction. |
4) Answer Question.
(a) What are the source of metals.
Answer: Ores are the source of metals.
(b) How is metallurgy a stepwise process?
Answer: metallurgy is the science and technology of extracting metals from their ores and refining them for use, involving a series of sequential steps. The general steps include:
(i) Grinding:
The process of crushing ores into the small fine particles using the machine roles is known as grinding.
(ii) Concentration:
Concentration is the process of removing impurities from the crushed ores.
(iii) Oxidation:
This is the process of converting ores or other metals into their oxides in the presence or absence of oxygen.
(iv) Reduction:
It is the process of removing oxides from the metal oxides.
(v) Refining:
The metals obtained after the Reduction may still contain some impurities so to obtain metals in pure state refining is done.
(c) make a list of ores of iron, copper, aluminium and silver.
Iron: Haematite (Fe2O3), magnetite (Fe3O4), Siderite.
Copper: Chalcopyrite (CuFeS2), Bornite (Cu5FeS4), Cuprite (Cu2O).
Aluminium: Bauxite (Al2O3·2H2O), cryolite (Na3AlF6).
Silver: Argentite (Ag2S), Horn silver (AgCl).
(d) How pure metals are obtained from electro-refining? Explain with an activity.
Answer:
Activity:
purifying impure copper by the method of electro-refining.
materials required:
voltameter, impure copper, pure copper plate, battery, copper-sulphate solution, or solution of any copper salts.
method:
Take the solution of copper sulphate in the voltameter. Connect impure copper to the positive terminal of the battery and the pure copper plate to the negative terminal of the battery. Thus by making copper an anode and pure copper as cathode. Now pass electricity into voltameter.
Observation:
The impure copper plate in anode erodes and pure copper gets deposited on the cathode.
Conclusion:
In this way, we can get the pure copper from its impure form by the process of electrolysis.
Discussion
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