Reactions of metals - class-VIII

Zinc metal burns in air only on strong heating to form zinc oxide.

 An amphoteric oxide is an oxide that can act as either an acid or base in a reaction.
$Al _2O _3$ is an amphoteric oxide. When reacted with HCl, it acts as a base to form the salt $AlCl _3$. When reacted with NaOH, it acts as an acid to form $NaAlO _2$.
also, zinc oxide is an amphoteric oxide.

Magnesium is a metal that burns in oxygen with a bright light and the reaction can be written as:
$2Mg + O _{2} \rightarrow 2MgO$

The metal stored in kerosene oil is Sodium(Na).

$ Zn + H _{2}O \rightarrow ZnO + H _{2}$
          (steam)

The metals which react with cold water are; sodium, calcium and magnesium.

Copper, silver and gold are unreactive metals and do not react with water or mild acids. 

Gold is a noble metal which does not react with oxygen on heating.

All the alkali metals react vigorously with cold water. In each reaction, hydrogen gas is given off and the metal hydroxide is produced. The speed and violence of the reaction increases as you go down the group. This shows that the reactivity of thealkali metals increases as you go down group 1. And sodium is a group 1 element.

Metals react with water to form alkaline metallic hydroxides.
$Ca+{ H } _{ 2 }O\rightarrow Ca\left( OH \right) _{ 2 }\downarrow +{ H } _{ 2 }\uparrow $

All metal oxides loses oxygen and are therefore reduced. Metals always occur in their oxidized state in ores. In order to convert an ore to its elemental state, it is reduced.

Metals react with air (oxygen) to form metal oxides. Metals react with oxygen to form basic oxides or amphoteric oxides. 

Metals reacts with water to form a metal hydroxide or metal oxides and hydrogen gas.

When zinc reacts with steam it produces zinc oxide and releases hydrogen gas.

The metal $M$ is copper $(Cu)$ which reacts with oxygen when heated in the air to form black coloured copper(ll) oxide. The reaction can be written as:
$2Cu + O _{2} \rightarrow 2CuO$

Magnesium and zinc do not react with cold water. They form their respective oxides when reacted with hot water.
$   Mg        +          H _2O         \rightarrow           MgO         +       H _2  $
                            (hot water)

Sodium metal is very reactive. It reacts vigorously with oxygen and water. A lot of heat is generated in this reaction. Hence, it is stored in kerosene.

Metals like Na, K react violently with cold water to evolve hydrogen gas that catches fire. Ca on other hand, reacts less violently with cold water giving out hydrogen gas which does not catch fire.

Sodium metal is very reactive. It reacts vigorously with oxygen and water. A lot of heat is generated in this reaction. Hence, it is stored in kerosene. To test for the release of hydrogen gas, place a lighted splint over the reacting metal - if it "pops" then hydrogen is present.

Sodium is a light and soft metal that reacts vigorously with cold water. Sodium when dropped in cold water forms a ball and moves on the surface of cold water with sodium hydroxide formation accompanied with the release of hydrogen gas.
$2Na+2H _2O \rightarrow 2NaOH +H _2$

Metals like aluminium, zinc, iron do not react with hot/cold water ; they react only with steam to form a metal oxide and hydrogen .

Sodium is highly reactive with cold water forming hydroxides and hydrogen gas. Hence, sodium is always stored under kerosene. Mercury, zinc and tungsten are found in the reactivity series at the bottom and are not highly reactive compared to sodium.

Metals form basic or amphoteric oxides while non metals form acidic oxides.

Aluminium is soft silvery metal, yet the surface gets tarnished due to the formation of film of its oxide $Al _2O _3$.
When aluminium is exposed to moist air a thin film of  oxide layer which is thin, hard and adhering.
$4Al+3O _2 \rightarrow 2Al _2O _3$

Metal + Oxygen $\rightarrow$ Metallic oxide

Actually the oxides of metals like Zn,Pb and other metals which are not very reactive can be reduced by Carbon. However oxides of very reactive metals (eg Aluminium,Chromium) can't be reduced by Carbon . Since they are very reactive they react with carbon to form their carbides hence are not effective in reduction.

Lead, copper, silver, and gold are low in the reactivity series. They do not react with cold or hot water, nor with steam, unlike highly reactive metals like sodium or potassium.

$2Al(s) + 3H _2O(g) \rightarrow Al _2O _3(s) + 3H _2(g)$

$2K(s) + 2H _2O(l) \rightarrow $2$KOH$(aq) + $H _2(g)$ + heat energy

Hydrogen gas is formed when magnesium reacts with water to form its hydroxide as Mg is highly reactive with water and acids. It is present on the top of the activity series. So, it is a very reactive metal.

$4Al(s) + 3O _2(g) \rightarrow 2Al _2O _3(s)$

The metals, which are low in the reactive series, undergo reduction reaction. Their metal oxides react with carbon to reduce the metal oxide to its metal and form an oxide of carbon.
$2CuO+C \rightarrow 2Cu+CO _2$

Metals from magnesium to iron in the activity series of metals, react with steam (but not $H _2O$) to form the metal oxide and hydrogen gas.

Metal forms basic oxides which reacts with water and forms base as
$M-2e^- \rightarrow M^{+2}$
$MO+H _2O \rightarrow M(OH) _2$

Magnesium has almost no reaction with cold water. It reacts very slowly with hot water.  It reacts with steam when being heated and gives hydrogen gas and metal oxide.
Magnesium + Water $\rightarrow$  Magnesium hydroxide + Hydrogen gas
Zinc and iron do not react with cold or hot water.  They react with  steam slowly to give the respective oxides:
Zinc + Steam $\rightarrow$  Zinc oxide  + Hydrogen gas
Iron + Steam $\rightarrow$ Iron(II) iron(III) oxide  + Hydrogen gas

The reactivity of active metals can be demonstrated by dropping pieces of $Li, Na, K$ into water. $Li$ reacts slowly with water, $Na$ reacts more rapidly and $K$ reacts violently. For a reaction between sodium and water, it can be divided into two halves. One-half reaction describes what happens when sodium atoms lose electrons. The other half describes what happens when water molecules gain these electrons. An overall equation is obtained for the reaction which shows the formation of metal hydroxide and evolution of hydrogen gas.
$2Na\left( s \right) +2{ H } _{ 2 }O\left( l \right) \rightarrow 2{ Na }^{ + }\left( aq \right) +2{ OH }^{ - }\left( aq \right) +{ H } _{ 2 }\left( g \right) \uparrow $

Zinc is a metal which doesnot react with cold water but reacts with steam. The chemical equation for the reaction can be written as:
$ Zn + H _{2}O \rightarrow ZnO + H _{2}$
         (steam)

Compounds which have the ability to react as both an acid or base are known as amphoteric in nature. 

Lead oxide is prepared by calcination of lead II oxide in air at about 450 to 480C.
$6PbO+{ O } _{ 2 }\rightarrow { 2Pb } _{ 3 }{ O } _{ 4 }$

Reaction:
$\displaystyle 3Fe+4H _{2}O\rightarrow 1Fe _{3}O _{4}+4H _{2}$

Sodium is a highly reactive metal of alkali group and on exposure to air it forms sodium hydroxide while calcium is not reactive in nature so it is not stored in kerosene.

Metal oxides typically contain an anion of oxygen in the oxidation state of -2. Oxides which are reacted only by acids are basic oxides. Metals form basic oxides so they can turn red litmus blue as it is alkaline in nature.

The reaction takes place as

$2Na+H _2O\rightarrow 2NaOH+H _2+Heat$

Aluminium is oxidized by water at temperatures below $280^oC$  to produce hydrogen, aluminium hydroxide and heat. The challenge in this reaction is circumventing the formed oxide layer which inhibits the reaction and the expenses associated with the storage of energy by regeneration of $Al$ metal.

Beryllium $(Be)$ is the only alkaline earth metal that does not react with water. This is due to its small size and high ionization energy in relation to the other elements in the group.

When steam is passed over red hot iron, $H _2$ and $Fe _3O _4$ are formed. The reaction is as follows:
$3Fe+4{ H } _{ 2 }O\rightarrow { Fe } _{ 3 }{ O } _{ 4 }+4{ H } _{ 2 }\uparrow $

Zinc is a moderately reactive metal that does not react with cold water and hence no gas is evolved.

$Zn+H _2O \rightarrow $ No reaction.

Magnesium burns in steam to produce white magnesium oxide and hydrogen gas. If a metal reacts with cold water the metal hydroxide is formed but if it reacts with steam the metal oxide is formed.

Iron is less reactive than sodium, potassium, calcium, zinc and magnesium. It does not react with cold and hot water, but it reacts with steam to form magnetic oxides.
$ 2Fe(s) + 3H _2O(g) \rightarrow Fe _2O _3(s) + 3H _2(g) $

When sodium is added to water, the sodium melts to form a ball that moves around on the surface. It fizzes rapidly, and the hydrogen produced may burn with an orange flame before the sodium disappears.When potassium is added to water, the metal melts and floats. The hydrogen ignites instantly. The metal is also set on fire, with sparks and a lilac flame. 

Metals like sodium and potassium react violently with cold water. These reactions are exothermic. The reaction is so violent and exothermic that the hydrogen which is evolved immediately catches fire.

Metallic substance exists as cations with delocalized electrons.
The positive ions (cations) are arranged to form a kernel in the sea of delocalised electrons. The force of attraction between the positive ions (cations)  and  the sea of delocalised electrons is called the metallic bond.

$ 2K + 2H _2O \rightarrow 2KOH + H _2$

Reaction of 'Na' with cold water. 

Sodium with cold water produces $\displaystyle NaOH, : H _2$
$\displaystyle 2Na + 2H _2O \rightarrow 2Na^+  + 2 OH^- + H _2 \uparrow $

Alkali earth metals (Ca, Sr, Ba) react, vigorously with cold water.
Be does not react even with boiling water. Mg reacts with boiling water.

Potassium's reaction with water produces hydrogen gas of bluish pink.
Potassium reacts with cold water and gives potassium hydroxide and hydrogen gas.
$\displaystyle 2K + 2H _2O \rightarrow 2KOH + H _2$
The reaction is exothermic and the resulting solution is basic.
The reaction is so vigorous that the evolved hydrogen catches fire spontaneously.

Sodium in water catches fire due to formation of hydrogen gas and evolution of heat.
$\displaystyle 2Na + 2H _2O \rightarrow 2Na^+ + 2OH^- + H _2 \uparrow$
Note: In exothermic process, heat is released. The reaction of Na with water is highly exothermic. Due to rapid increase in temperature, hydrogen gas catches fire.

The reaction of potassium and water is  exothermic in nature.
Potassium explosively reacts with water to form KOH with evolution of hydrogen gas.
$\displaystyle 2K + 2H _2O \rightarrow 2K^+ + 2OH^- + H _2 \uparrow$
Note: In exothermic process, heat is released. When KOH is added to water, the temperature of resulting solution rapidly increases.

Calcium reacts vigorously even with cold water and forms calcium hydroxide and liberates hydrogen gas.
$\displaystyle Ca+2H _2O \rightarrow Ca(OH) _2 + H _2 \uparrow$
Hence, the option (A) is the correct answer.

Calcium reacts with cold water and forms calcium hydroxide $\displaystyle Ca(OH) _2$.
$\displaystyle Ca + 2H _2O \rightarrow Ca(OH) _2 + H _2$

Ca reacts with cold water to form calcium hydroxide and hydrogen
$Ca + 2H _2O \rightarrow Ca(OH) _2+H _2 \uparrow $

Metals react with cold water and gives metal hydroxide and hydrogen.
For example, sodium reacts with cold water and gives sodium hydroxide and hydrogen gas.
$\displaystyle 2Na + 2H _2O \rightarrow 2NaOH + H _2$

The piece of sodium melts in water at, $\displaystyle 97.8^oC$
Sodium reacts with cold water and gives sodium hydroxide and hydrogen gas.
$\displaystyle 2Na + 2H _2O \rightarrow 2NaOH + H _2$
The reaction is exothermic and releases the heat. The heat released melts Na. Then Na may disappear.  
The heat may burn hydrogen with an orange flame.

Sodium reacts with cold water and gives sodium hydroxide and hydrogen gas. The balanced chemical equation is

When potassium is added to water, it burns with a lilac flame.

The resulting solution is basic because of the dissolved hydroxide. The reaction is exothermic. 

$X$ is copper $(Cu)$ and the black-coloured compound formed is copper oxide $(CuO)$. The equation of the reaction involved on heating copper in given below.

When potassium reacts with water, a colourless basic solution is obtained.
 When potassium is added to water potassium hydroxide (a strong base) and hydrogen gas are obtained. The reaction of
potassium with water is exothermic.
$2K + 2H _2O \rightarrow 2KOH + H _2$

The metal sodium, calcium and magnesium are highly reactive to water and make their hydroxides. 
Iron is a less reactive metal and does not show any reaction while treated with cold as well as hot water but will react with steam and form metal oxides and hydrogen gas.
$3Fe(s) +4H _2O(g) \rightarrow Fe _3O _4(s)+4H _2(g)$
  Iron         Steam          Iron(III) oxide   Hydrogen

Alkali metal $(A)$ is sodium ($Na$) which forms $NaOH$ (compound $B$) with water .The reaction can be written as:
$2Na + 2H _{2}O \rightarrow  2NaOH + H _{2}$
$NaOH$ reacts with aluminium oxide($ Al _{2}O _{3}$) to form sodium aluminate (compound $C$) with chemical formula $NaAlO _{2}$.The reaction can be written as:
$Al _{2}O _{3} + 2NaOH \rightarrow  2NaAlO _{2} + H _{2}O$

Sodium and magnesium metal reacts with the oxygen of the air at room temperature to form sodium oxide and magnesium oxide respectively. These oxides react with water to form hydroxides.
$4Na + O _2 \rightarrow 2Na _2O$
$Na _2O + H _2O \rightarrow 2NaOH$
$2Mg + O _2 \rightarrow 2MgO$
$MgO + H _2O \rightarrow Mg(OH) _2$

Zinc only when heated replaces hydrogen from steam thus forming oxides.