Class 10 Science
Chapter 3 Metals And Non Metals
Activity Solutions
Activity 3.1
Brief procedure:
Activity 3.1 asks us to check the appearance of some metals and see changes it after rubbing it with sandpaper.
Observation:
We see these metals look dull.
After rubbing with sandpaper all these materials shine.
Explanation:
Metals like iron, copper, magnesium, sodium are reactive metals. These metals react with oxygen and form their oxide on the outer layer. Metal oxides are dull in colour. As a result, the metal loses its lustrous property.
e.g. Iron forms a brown layer which we call rusting of iron; aluminium forms smoke colour aluminium oxide; copper forms a black and green layer with oxygen and sulphur etc.
When we rub the metals with sandpaper, its outer oxide layer is scraped out.
You may recall the burning of magnesium in chapter one. here we first clean the magnesium ribbon. It was because magnesium oxide interferes in burning. See: Why should a magnesium ribbon be cleaned before burning?
Interesting fact:
Silver, gold, platinum are very less reactive metals. They do not react with atmospheric air or water. As a result, their shine persists longer, and people use them as jewelry items.
Activity 3.2
Brief procedure:
Activity 3.2 asks us to cut various metals and note the observation.
Observation:
Metals are hard and can not be cut easily. Only magnesium is easily cut. Aluminium require more effort while iron is very hard to be cut by a knife.
Explanation:
Atoms of a metal are stongly connected to its neighbor atoms by a strong attractional force. This makes them hard and difficult to be cut.
Inference/conclusion:
This experiment demonstrates metals have strong inter moleculare force of attraction and are difficult to cut.
Extras
In case of aluminium the there is a shiny layer below the outer layer.
This happens because the outer layer of metals reacts with the atmospheric oxygen to form metal oxides. Metal oxides do not have lustrous property. When we cut the metals using a knife its inner unoxidised layer come into view which shines.
Application:
Metal oxides are a bad conductor of electricity. The oxidation of metals in an electric component may lead to failure. So, we coat metals in circuit with unreactive metals like gold in costly computer parts. It saves them from oxidation.
Activity 3.3
Brief procedure:
Activity 3.3 asks us to strike a metal with a hammer and observe what happens.
Observation:
Metal become thin, and it’s surface area increases.
Explanation:
When we hit metal with a hammer or other hard objects metal spreads into a thin sheet. We call this property of metal Malleability.
Inference/conclusion:
This experiment shows that metals are malleable.
Application:
Blacksmith: A blacksmith ( Lohar) heats an iron rod in the furnace and then beats with a hammer until he gets the desired shape.
Steel sheet on the roof is also an application of this property.
Activity 3.4
Brief procedure:
Activity 3.4 asks us to list some metals which find its use in the wire.
Answer:
Aluminium, copper, nickel, chromium, gold, silver.
Application:
In normal homes, we use aluminium (white core) or copper wire (Golden colour). Now Aluminium wires are less common as copper wires are a better conductor of electricity.
An electric wire on pole still uses aluminium wire because the copper wire is very costly.
Nickel and chromium have lesser conductivity. They are mixed to form nichrome wire. Some wired electric heater consists of nichrome wire.
Apart from all these metals, precious metals like silver and gold also find use in the electronic industry as wire.
They have very high thermal and electrical conductivity. As a result, we use them as a coating in high-quality switches and plugs.
Some electric circuits also consist of silver or gold wires.
Activity 3.5
Brief procedure:
The activity asks us to heat a metal wire which is attached to a pin at its corner by a wax.
Observation:
The pin drops immidiately once we start heating the wiwires.
Explanation:
Metals are a good conductor of heat. Here, once we start heating, heat transfers to the area of wax. It melts the wax. So, the pin drop on the table.
Inference/conclusion:
This experiment demonstrates that metals are a good conductor of heat
Application:
Processor cooler in computers and laptops: In a computer and a laptop CPU is the most important chip. During data processing, it generates a lot of heat. To dissipate the heat, a CPU is connected to a copper or aluminium heat sink. Due to the thermal conductivity of metals heat transfers to the heat sink. A fan at the sink blows the hot air outside.
Cooking utensils: Cooking utensils consists of a metal or metal alloys. It receives heat from the gas stove and transfers heat to the food.
Facts:
Metals have free electrons in their valance shell. When we heat a metal, their electrons vibrate and transfer heat to another electron. As a result, metals are a good conductor of heat.
Activity 3.6
Brief procedure:
Activity 3.6 asks us to connect a metal wire with a bulb in series and see what happens to the bulb.
Observation:
The bulb glows as bright as earlier.
Explanation:
Metals have free electrons in their valance shells. These free electrons move from one position to another. As a result, metals are a good conductor of electricity. When we connect a build to the battery by metal wires, electricity passes from the battery to the bulb. As a result, the bulb starts glowing.
Inference/conclusion:
This experiment demonstrates that metal wires are a good conductor of electricity.
Application:
In making wires at home, in making electric circuit board etc.
Some Facts:
When someone is electrocuted, we do not use a metal stick but we use a wooden or plastic stick. Metal stick or rods are good conductors of electricity. If someone tries to save an electrocuted person by that stick, he himself will get electrocuted.
Activity 3.7
Brief procedure:
Activity 3.7 asks us to compare the properties of metals discussed in earlier activities with some common non-metals.
Answer:
In activities from 3.1 to 3.6, we studied various properties of metals. They are:
1. Lusture 2. Hardness 3.Malleability 4. Ductility 5. Electric conductivity 6. Heat conductivity.
Metals generally carry all these properties except a few like mercury which is soft (liquid), Sodium and lithium which are not hard. Most non-metals have contrasting features with few exceptions like coal and graphite and diamond which are hard. Below table summarises the properties of some common non-metals.
Activity 3.8
Brief procedure:
Activity 3.8 asks us to react oxides of metal and non-metals with water and check if it is acidic or basic in nature.
Observation:
We get metal oxide by burning the metal in the presence of oxygen. Metal oxide reacts with water to give a base. It turns the red litmus paper blue.
Similarly, the burning of non-metal produces its oxide. The solution of oxides of non-metal with water turns the blue litmus paper into the red.
Explanation:
Magnesium
Magnesium burns in air to form its oxide. See activity 1.1.
2Mg(s) + O2(g) ———–> 2MgO(s)
Magnesium oxide reacts with water and forms Magnesium Hydroxide.
MgO(S) + H2O(l) ———–> Mg(OH)2 (aq)
Magnesium hydroxide is a strong base. It makes the solution alkaline. So, the PH paper turns blue.
Application:
Many antacid syrups contain metal oxides like magnesium oxide and aluminium oxides. These metal oxides form respective metal hydroxide in the stomach and neutralises the acidity.
Sulphur:
Sulphur is a reactive non-metal; it burns to produce its oxide.
S(s) +O2(g) ————-> SO2(g)
Sulphur dioxide dissolves in water and forms sulphurous acid.
SO2(g) + H2O(l) ———–> H2SO3 (aq)
Sulphurous acid is a weak acid. Its 0.1N solution gives the PH of 1.5 which turns the blue litmus red.
Activity 3.9
Brief procedure:
Activity 3.9 asks us to burn various metals and observe their flame.
Observation:
Not all metals burn easily, Copper and aluminium take time to burn.
Flame colour:
Sodium: Yellow
Magnesium: White
Aluminium: Silver white
Copper :blue flame
Solubility:
Highly reactive metals like sodium and potassium reacts with water and form soluble hydroxide. But most other metals are not so reactive. So they are not soluble in water.
Only some metal oxides that from metal hydroxide with water, are soluble in water. Else they are insoluble. Beryllium and magnesium are exceptions as they are slightly soluble in water.
Metal oxide + H2O(l) ———> Metal Hydroxide.
Explanation:
Metals are highly reactive elements. They react with oxygen readily to form metal oxides. Highly reactive metals like lithium, sodium, potassium, beryllium, magnesium react spontaneously. Other metals like Aluminum, copper take time to burn. It produces a specific flame colour. Many times flame colour is used to find the constituent of the substance.
Metal + O2(g) ———> Metal oxide(s)
Inference/conclusion:
Metals on the heating burn to produce its oxides. During this process, they produce characteristic flames.
Activity 3.10
Brief procedure:
Activity 3.10 asks us to react to various metals with water and observe the reaction.
Observation:
Reaction with cold water:
Metals like sodium and potassium vigorously react with water to form its oxide and hydrogen gas. Their reaction is so violent that hydrogen gas catches fire immediately.
2Na(s) + 2H2O(l) ———-> 2NaOH(aq) + H2(g)
2K(s) + 2H2O(l) ———-> 2KOH(aq) + H2(g)
Reaction with hot water:
Calcium is less reactive than sodium and potassium with cold water. They react spontaneously and emit hydrogen bubbles. But, the reaction is not so violent and hydrogen gas does not catch fire.
Ca(s) + 2H2O(l) ———-> Ca(OH)2(aq) + H2(g)
Metals like iron, zinc and aluminium do not react with cold or hot water. They react with steam to form corresponding hydroxide and hydrogen gas.
2Al(s) + 6H2O(l) ———-> 2Al(OH)3(aq) + 3H2(g)
No reaction:
Metals like lead, copper, silver and gold do not react with any form of water.
Order of reactivity with water in descending order:
Na>K>Ca>Zn>Fe>Al
Inference/conclusion:
Metals react with water and form metal hydroxide. It produces hydrogen gas, which we can check by placing a match-stick near it.
Activity 3.11
Brief procedure:
Activity 3.11 asks us to react to various metals with dilute hydrochloric acid and observe the reaction.
Observation:
Metals react with dilute hydrochloric acid and form metal chlorides with the evolution of hydrogen gas.
Metal(s) + HCl(aq) ———–> Metal Chloride(aq) + H2(g)
E.g.
Ca(s) + 2HCl(aq) ————-> CaCl2(aq) + H2(g)
Order of reactivity:
Ca>Mg>Al>Zn>Fe>Pb>Cu
Reaction of metals with dilute hydrochloric acid
Temperature during the reaction:
Experiment done at room temperature (25˚C).
Calcium: 40˚C
Zinc: 34˚C
Iron: 30˚C
Copper: 25˚C
Inference/conclusion:
Metals react with acids to form their salt. The process is exothermic and hydrogen gas is also produced.
Activity 3.12
Brief procedure:
Activity 3.12 asks us to dip copper and iron nail into a salt solution of another metal and observe the reaction.
Observation:
More reactive metals displace with metals from other salt solution and form corresponding salts.
e.g., Iron in a copper sulphate solution.
Explanation:
Iron is more reactive than copper. It displaces copper from copper sulphate and forms ferrous sulphate. Copper sulphate solution is blue while ferrous sulphate is green. So the solution turns green from blue.
Fe(s) + CuSO4(aq) ———–> FeSO4(aq) + Cu(s)
Note: The diplacement depend on reactivity series. A metal can displace a salt if the metal is higher in reactivity series.
Reactivity Series of Metals.
Activity 3.13
Brief procedure:
Activity wants us to find the various properties of various salts like physical nature, melting point, solubility, conduction of electricity.
Salts of acids and bases are Hard; brittle; have a high melting point; soluble in water; insoluble in non-polar solvents like kerosene, benzene; conducts electricity.
Explanation:
Molecules of salt are closed together by the strong Ionic bond between anions and cations. This strong attraction gives a salt hard appearance, high melting and boiling point.
In water and other polar solvents, they form strong ionic bonds, so they are soluble in water. Non-polar solvents like organic solvents and kerosene do have polar bonds. A salt molecule, therefore, does not mix with such solvents. As a result, it sinks to the bottom.
In solution form molecules of salts are in ionic form. They move freely in the solution; therefore they conduct electricity.
Note:
For any doubt, think about sodium chloride and solve the question.
Activity 3.14
Brief procedure:
Activity 3.14 asks us to experiment with iron nails in various conditions.
A. Iron dipped in water B. Nail dipped in water with some oil floating on water. C. Iron nail with calcium chloride.
Observation:
Nails in test tube A got rusted in a few days. Nails in test tube B and C did not get rust.
Inference:
It shows water and air both are necessary to form rust.
Explanation:
Oxidation of iron metal with oxygen require high temperature. The other alternative is to use the hydration energy of water. The outer layer of iron nail reacts with oxygen in the presence of water to form its oxide.
4Fe(s) + 6H2O(l) + 3O2(g) ———-> 2Fe2O3*3H2O
Outer layer now scrapes off and give way to oxygen and moisture to the inner layer of iron. The process goes on until all iron convert into its oxide.
In the test tube, B oil prevents oxygen from dissolving in water. In the test tube C, calcium chloride acts as an absorbent and absorbs moisture present in it. So, Iron does not form rust in these test tubes.
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