Reactions of metals - class-VIII

 Description: reactions of metals Number of Questions: 92 Created by: Shaka Gupte Tags: metals reactivity series and electrochemistry metals and metallurgy chemistry metals and non-metals metallurgy
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Zinc metal burns in air only on strong heating to form :

1. zinc chloride

2. zinc sulphide

3. zinc oxide

4. zinc hydroxide

Correct Option: C
Explanation:

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

$Zinc + Oxygen \xrightarrow{\Delta} Zinc\,oxide$

$2Zn + O _2 \xrightarrow{\Delta} 2ZnO$

When a copper vessel is exposed to moist air for a longer time. It aquires a dull green coating then the correct statement is

1. It contains copper hydroxide

2. It contains copper carbonate

3. It is formed when copper reacts with moist air

4. None of these

Correct Option: A

The amphoteric metallic oxide is:

1. calcium oxide

2. barium oxide

3. zinc oxide

4. copper (II) oxide

Correct Option: C
Explanation:

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.

Which one of the following is basic oxide?

1. Nitrous oxide

2. Nitric oxide

3. Carbon monoxide

4. Zinc oxide

Correct Option: D
Explanation:
Metals generally form basic  oxides, some of which are also amphoteric, such as aluminium  oxide, zinc oxide, lead oxide etc.
Non-metals generally form acidic oxides. Some oxides are neutral, such as nitrous oxide, nitric oxide, carbon monoxide water etc.

Name one metal in each part fitting the given description:

A metal that burns in oxygen with a bright light

1. Magnesium

2. Iron

3. Aluminium

4. None of the above

Correct Option: A
Explanation:

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

Which metal is stored in kerosene oil?

1. Sodium

2. Calcium

3. Iron

4. None of the above

Correct Option: A
Explanation:

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

Name two product of the given reaction.

$Zn + \underset{(Steam)}{H _2O} \rightarrow$

1. Zinc oxide, hydrogen

2. Zinc, water

3. Zinc oxide, water

4. Zinc, hydrogen

Correct Option: A
Explanation:

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

Which metals react with cold water?

1. Sodium, calcium, magnesium

2. Iron, calcium, magnesium

3. Iron, sodium, magnesium

4. Potassium, sodium, magnesium

Correct Option: A
Explanation:

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

Which metal does not react with water?

1. $Cu$

2. $Au$

3. Both A and B

4. $Fe$

Correct Option: C
Explanation:

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

Which of the metals will not react with oxygen when heated?

1. Gold

2. Iron

3. Sodium

4. None of the above

Correct Option: A
Explanation:

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

A metal which reacts with cold water vigorously producing hydrogen is:

1. zinc

2. hydrogen

3. sodium

4. mercury

Correct Option: C
Explanation:

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.

The correct option is C.

When a metal reacts with water it forms:

1. alkalies

2. basic oxide

3. dilute acid

4. neutral acid

Correct Option: A
Explanation:

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

Oxides of which of the following metals is reduced by aluminium powder?

1. Magnesium

2. Potassium

3. Chromium

4. All of the above

Correct Option: D
Explanation:

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 oxygen to form:

1. acids

2. $H^+$ ions

3. metal oxides

4. all of the above

Correct Option: C
Explanation:

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 $\ {W}$.

1. $W =$ acidic oxide, carbon dioxide

2. $W =$ basic oxide, heater

3. $W =$ metal oxide, hydrogen

4. $W =$ metal hydroxide, oxygen

Correct Option: C
Explanation:

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

What are the products formed when zinc reacts with steam?

1. Zinc hydroxide and oxygen

2. Zinc hydroxide and hydrogen

3. Zinc oxide and oxygen

4. Zinc oxide and hydrogen

Correct Option: D
Explanation:

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

A metal $M$ does not liberate hydrogen from acids but reacts with oxygen to give a black colour product. Identify black coloured product is:

1. $MgO$

2. $CuO$

3. $FeO$

4. $ZnO$

Correct Option: B
Explanation:

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:
$2Cu + O _{2} \rightarrow 2CuO$

$Mg + H _2O \rightarrow$

(cold water)

1. $MgO + H _2$

2. $Mg _2O + H _2$

3. $MgO + H _2O$

4. The above reaction cannot occur

Correct Option: D
Explanation:

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)

Why is sodium stored in kerosene?

1. It evaporates

2. It is highly reactive

3. It burns

4. All of above

Correct Option: B,C
Explanation:

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 K, Na react ______ with cold water whereas Ca reacts_____ with cold water.

1. Violently, less violently

2. Mildly, violently

3. Violently, violently

4. Mildly, does not react

Correct Option: A
Explanation:

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.

What does the pop sound indicate when sodium reacts with cold water?

1. Release of oxygen

2. Release of carbon dioxide

3. Both A and B

4. Release of hydrogen

Correct Option: D
Explanation:

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.

Which of the following reacts with cold water vigorously?

1. Carbon

2. Sodium

3. Magnesium

4. Sulphur

Correct Option: B
Explanation:

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

Which of the following metal reacts with steam but not hot/cold water?

1. Al

2. Zn

3. Fe

4. All of above

Correct Option: D
Explanation:

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

The metal that reacts with cold water is :

1. mercury

2. sodium

3. zinc

4. tungsten

Correct Option: B
Explanation:

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 combine with oxygen to form _________ oxides.

1. basic

2. acidic

3. neutral

4. both A and B

Correct Option: A
Explanation:

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

Aluminium does not oxidize readily in air because :

1. it is high in the electrochemical series

2. it is low in the electrochemical series

3. the metal does not combine with oxygen

4. the metal is covered with a layer of oxide which does not rub off

Correct Option: D
Explanation:

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 reacts with oxygen to form _________ .

1. Acid

2. Base

3. Metallic oxide

4. Non-metallic oxide

Correct Option: C
Explanation:

Metal + Oxygen $\rightarrow$ Metallic oxide

Example:
$2Mg(s) + O _2(g) \rightarrow 2MgO(s)$

In which molecules s-p overlapping occurs?

1. $CH _{4}$

2. $NH _{3}$

3. $H _{2}O$

4. None of these

Correct Option: B
Explanation:

s-p overlapping one such type of overlapping. Here there is a overlapping between the s- and p- orbital's of the molecules. This type of overlapping is generally seen in the NH3 molecules. This formed by overlapping between 3 orbital's of hydrogen and 3 of nitrogen

Among the metals, the one that cannot be obtained by the reduction of its metal oxide.

1. $Cr$

2. $Fe$

3. $Mn$

4. $Mg$

Correct Option: A
Explanation:

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.

Metals such as lead, copper, silver and gold do not react with water at all.

1. Statement is False

2. Statement is True

3. Lead reacts but copper, silver, and gold do not

4. Copper reacts but lead, silver and gold do not.

Correct Option: B

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

1. $A=2Al(s);\, B= 3H _2O(g)$

2. $A=Al; \,B= 3H _20$

3. $A=Al; \,B=H _2SO _4$

4. No reaction possible

Correct Option: A
Explanation:

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

$2K(s) + 2H2O(l) \rightarrow$

1. $2KOH(aq) + H _2(g) +$ heat energy

2. $2KOH(aq) + H _2(g)$

3. $2KOH(aq) + H _2O(g) +$ heat energy

4. No reaction

Correct Option: A
Explanation:

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

The gaseous product formed when magnesium reacts with boiling water is :

1. hydrogen

2. washing soda

3. sulphurous

4. calcium oxide

Correct Option: A
Explanation:

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.

Aluminium reacts with oxygen to form ______ .

1. $AlO$

2. $AlO _2$

3. $Al _2O _3$

4. None of the above

Correct Option: C
Explanation:

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

Which of the following compounds can be reduced to copper when heated with coke?

1. Copper sulphate

2. Copper oxide

3. Hydrogen chloride

4. Ammonia

Correct Option: B
Explanation:

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.
$2CuO+C \rightarrow 2Cu+CO _2$

Name a metal which reacts with steam?

1. Sodium

2. Potassium

3. Lithium

4. Magnesium

Correct Option: D
Explanation:

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.

$\text{Magnesium + steam} \to \text{Magnesium oxide + Hydrogen}$
$Mg + H _2O \to MgO + H _2\uparrow$

Pertaining to metallurgy, when "M" is a metal, its oxide MO is :

1. acidic

2. basic

3. neutral

4. none of these

Correct Option: B
Explanation:

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

Name the following: A metal which does not react with cold water but reacts with steam.

1. Magnesium

2. Iron

3. Zinc

4. All of these

Correct Option: D
Explanation:

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

On reaction with water, an active metal produces:

1. oxygen

2. nitric acid

3. base

4. metal hydroxide

5. none of the above

Correct Option: D
Explanation:

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.
$2Na\left( s \right) +2{ H } _{ 2 }O\left( l \right) \rightarrow 2{ Na }^{ + }\left( aq \right) +2{ OH }^{ - }\left( aq \right) +{ H } _{ 2 }\left( g \right) \uparrow$

Metals combine with oxygen to produce:

1. neutral acid

2. basic oxide

3. acidic acid

4. amphoteric oxide

Correct Option: B
Explanation:
An oxide that combines with water to give an acid is termed as an acidic oxide. The oxide that gives a base in water is known as a basic oxide.
Generally Group 1 and Group 2 metals  form bases called base anhydrides or basic oxides e.g.,
$4K+O _2 \rightarrow 2K _2O$
Basic oxides are the oxides of metals. If soluble in water, they react with water to produce hydroxides (alkalies) e.g.,
$K _2O(s)+H _2O(l) \rightarrow 2KOH(aq)$)

Name one metal that will not react with cold water but will react with steam.

1. Zinc

2. Iron

3. Calcium

4. Magnesium

Correct Option: A
Explanation:

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)

Which of the following oxide is amphoteric in nature?

1. $Na _2O$

2. $Li _2O$

3. $K _2O$

4. $BeO$

Correct Option: D
Explanation:

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

$BeO$ is amphoteric in nature.

$Pb _3O _4$ a double oxide. is obtained by heating lead (II) oxide in air.

1. True

2. False

Correct Option: A
Explanation:

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

$\displaystyle xFe+yH _{2}O\rightarrow zFe _{3}O _{4}+wH _{2}$
What are x, y, z and w respectively ?

1. 1, 2, 3, 4

2. 2, 3, 1, 2

3. 3, 4, 1, 4

4. 3, 3, 3, 3

Correct Option: C
Explanation:

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

Calcium is stored in kerosene.

1. True

2. False

Correct Option: B
Explanation:

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.

Metals oxides are:

1. basic in nature

2. electrovalent (ionic) in nature

3. able to turn red litmus solution blue

4. all of these

Correct Option: D
Explanation:

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.

What happens when water vapour is passed over a red hot iron?

1. No reaction

2. Oxygen and $Fe{(OH)} _{2}$ are produced

3. Hydrogen and ${Fe} _{2}{O} _{3}$ are produced

4. Hydrogen and ${Fe} _{3}{O} _{4}$ are produced

Correct Option: D
Explanation:

The reaction takes place as

$3Fe + 4H _2O \rightarrow Fe _3O _4 + 4H _2$
so, on passing water vapour over hot red iron we get hydrogen and $Fe _3O _4$.

A silvery-white metal $X$ reacts with water at room temperature to produce a water-soluble compound $Y$ and a colourless gas $Z$. The reaction is highly exothermic and the $Z$ catches fire immediately during the reaction. The solution of $Y$ in the water on reacting with a stoichiometric amount of dilute solution of hydrochloric acid gives a solution of $pH = 7.0$.
The compounds $X,\ Y$ and $Z$ respectively are:

1. $Al,Al(OH) _3$ and $H _2$

2. Ag, AgOH and $H _2$

3. K, KCl and $H _2$

4. Na, NaOH and $H _2$

Correct Option: D
Explanation:

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

$NaOH+HCl\rightarrow NaCl+H _2O$
$X,\ Y,\ Z$ are $Na$, $NaOH$, $H _2$

Aluminium does not react with water at room temperature because:

1. it is above hydrogen in the activity series

2. it is below hydrogen in the activity series

3. it is covered with a thin film of $AlN$

4. it is covered with thin film of $Al _2O _3$

Correct Option: D
Explanation:

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.

Which of the following metal does not react with water?

1. Beryllium

2. Copper

3. Iron

4. Potassium

Correct Option: A
Explanation:

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.

What happens when steam is passed over red hot iron?

1. No reaction takes place.

2. $O _2$ and $Fe(OH) _2$ are formed.

3. $H _2$ and $Fe _3O _4$ are formed.

4. $H _2$ and $Fe _2O _3$ are formed.

Correct Option: C
Explanation:

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

Hydrogen is not obtained when Zn reacts with:

1. cold water

2. hot NaOH solution

3. dil. H$_2$SO$_4$

4. dil. HCl

Correct Option: A
Explanation:

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.

When a small piece of dry sodium is put in water, it reacts vigorously to produce:

1. nitrogen gas

2. hydrogen gas

3. carbon dioxide gas

4. sulphur dioxide

Correct Option: B
Explanation:
Most of the metals do not react with water. However,alkali metals react vigorously with water. Reaction of sodium metal with water: Sodium metal forms sodium hydroxide and liberates hydrogen gas along with lot of heat when reacts with water.
When sodium reacts with watersodium hydroxide is formed hydrogen gas as a byproduct that gets burnt with a bright flame making the reaction highly exothermic.

The incorrect statement among the following for magnesium metal is:

1. it burns in oxygen with dazzling white flame

2. tt reacts with cold water to form magnesium oxide and evolves hydrogen gas

3. it reacts with hot water to form magnesium hydroxide and evolves hydrogen gas

4. it reacts with steams to form magnesium hydroxide and evolves hydrogen gas

Correct Option: D
Explanation:

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.

$2Fe(s) + 3H _2O(g)\rightarrow$

1. $Fe _2O(s) + 3H _2(g)$

2. $Fe _2O _3(s) + 3H _2(g)$

3. $Fe _2O _3(s) + 3H _2O(g)$

4. None of above

Correct Option: B
Explanation:

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

In case of reaction between sodium and cold water, hydrogen burns with _______ flame, whereas, in case of reaction between potassium and cold water, hydrogen burns with _____ color.

1. Yellow, lilac

2. Orange, yellow

3. Orange, lilac

4. Lilac, yellow

Correct Option: C
Explanation:

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.

The reaction of sodium metal with cold water is

1. Endothermic

2. Exothermic

3. Both a and b

4. Neither a nor b

Correct Option: B
Explanation:

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.

What will be the colour of the blue cobalt chloride paper dipped in water?

1. Yellow

2. Blue

3. Pink

4. Green

Correct Option: C
Explanation:

Cobalt chloride paper is used to test for the presence of water. In this test, the colour of paper changes from blue to pink.

Hence the correct option is C.

Which of the following exists as cations with delocalized electrons?

1. Non-polar covalent substance

2. Polar covalent substance

3. Ionic substance

4. Metallic substance

5. Noble gas

Correct Option: D
Explanation:

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.

Carbon combines with water to form:

1. water gas

2. carbon gas

3. hydrogen gas

4. carbogen

Correct Option: A
Explanation:

Carbon reacts with water to form water gas
$C + H _2O \rightarrow CO + H _2$

Potassium reacts with water to form:

1. $KOH \ and \ H _2O$

2. $KOH \ and \ H _2$

3. $K(OH) _2 \ and \ H _2O$

4. $K(OH) _2 \ and \ H _2$

Correct Option: B
Explanation:

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

Which one of these gas is released when Na reacts with cold water?

1. $H _2$

2. $Cl _2$

3. $O _2$

4. $H _2O$

Correct Option: A
Explanation:

Reaction of 'Na' with cold water.

$2Na+H _{2}O\rightarrow Na _{2}O+H _{2} \uparrow$
The reaction stops with forming $Na _{2}O$ . Because, we used cold water. The reaction doesnt continue to form NaOH.

Temporary hardness of water is due to the :

1. bicarbonate ion

2. sulphate ion

3. chloride ion

4. nitrate ion

Correct Option: A
Explanation:

Hardness of water due to bicarbonate ion is temporary and can be removed by boiling or through precipitation with calcium hydroxide.

Hence the correct option is A.

Which of the following is added to remove permanent hardness of water?

1. baking soda

2. blue vitriol

3. washing soda

4. milk of magnesia

Correct Option: C
Explanation:

By adding Na$_{2}$Co$_{3}$, all the Ca$^{+2}$ and and Mg$^{+2}$ ions which causes permanent hardness are replaced by Na$^{+}$, which doesn't cause hardness.

Permanent hardness of water is due to

1. bicarbonate ion

2. sulphate ion

3. nitrate ion

4. phosphate ion

Correct Option: B
Explanation:

Permanent hardness of water is due to sulphate ion and chloride ion and cannot be easily removed. It can be removed by treating with washing soda.

Which one of these can be called as natural water?

1. spring water

2. well water

3. river water

4. All of the above

Correct Option: D
Explanation:

Spring water, well water, and river water all are natural water.

Hence the correct option is D.

Sodium with cold water produces,

1. NaOH, $H _2$

2. NaH, $H _2$

3. $Na(OH) _2$

4. None of these

Correct Option: A
Explanation:

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

Sodium hydroxide in water gives

1. yellow color solution.

2. green color solution.

3. colorless solution.

4. light pink solution.

Correct Option: C
Explanation:

Sodium hydroxide in water gives colorless solution.
Sodium hydroxide is colourless. In water, it dissociates into sodium ions and chloride ions. These ions are also colourless.
$\displaystyle NaOH (aq) \xrightarrow{H _2O} Na^+ (aq) + OH^- (aq)$

Alkali earth metal react:

1. vigorously with cold water.

2. violently with hot water.

3. normally with water.

4. endothermically with water.

Correct Option: A
Explanation:

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

1. bluish pink.

2. greenish blue.

3. orange.

4. light pink.

Correct Option: A
Explanation:

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.

Sea water contains around:

1. 400 ppm calcium.

2. 500 ppm calcium

3. 100 ppm calcium.

4. 350 ppm calcium.

Correct Option: A
Explanation:

Sea water contains around 400 ppm calcium. In lithosphere, the occurrence of Ca is 4.6% by weight. Of the alkaline earth metals, calcium rank fifth in abundance in the earth crust.

Sodium in water catches fire due to formation of,

1. hydrogen gas and evolution of heat.

2. nitrogen gas and evolution of heat.

3. hydrogen gas and absorption of heat.

4. sulfur gas.

Correct Option: A
Explanation:

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 ______ in nature.

1. endothermic

2. exothermic

3. electron donating

4. electron withdrawing

Correct Option: B
Explanation:

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 __________ with water and forms calcium hydroxide and liberates hydrogen gas.

1. vigroushly

2. slowly

3. violently

4. uniformally

Correct Option: A
Explanation:

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.

The solution of KOH is

1. acidic in nature.

2. basic in nature.

3. neutral in nature.

4. alcoholic.

Correct Option: B
Explanation:

The solution of KOH is  basic in nature.
KOH is strong electrolyte and completely dissociates in aqueous solution to provide hydroxide ions. Due to this, aqueous KOH solution is strong alkali.
$\displaystyle KOH \rightarrow K^+ + OH^-$

Sea water is :

2. good conductor of electricity

3. impure form of ions

4. Both B and C

Correct Option: D
Explanation:

Since sea water contains many mineral ions hence it is good conductor of electricity and is present in impure form.

Hence the correct option is D.

Calcium reacts with cold water and forms

1. $Ca(OH) _2$

2. $CaO$

3. $Ca$

4. $CaO _2$

Correct Option: A
Explanation:

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

$Ca+ \text{cold water} \rightarrow$
What will be the products formed in the above reactions?

1. $Ca(OH) _2+H _2O$

2. $Ca(OH) _2+H _2$

3. $CaO+H _2$

4. No reaction

Correct Option: B
Explanation:

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

Give the melting point of sodium in degrees Kelvin and degrees Fahrenheit.

1. 370.95 Kelvin, 274 Fahrenheit.

2. 370.95 Kelvin, 280 Fahrenheit.

3. 371 Kelvin, 208.04 Fahrenheit.

4. 370.95 Kelvin, 208.04 Fahrenheit.

Correct Option: D
Explanation:

97.8 C = 370.95 Kelvin = 208.04 Fahrenheit.

Metals react with cold water and gives

1. metal oxide

2. metal oxide and oxygen

3. metal oxide and hydrogen

4. metal hydroxide and hydrogen

Correct Option: D
Explanation:

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:

1. $98^oC$

2. $97.8^oC$

3. $93^oC$

4. $97^oC$

Correct Option: B
Explanation:

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.

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

Balance the following reaction.

1. $2Na+2H _2O\rightarrow 2NaOH+H _2$

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

3. $2Na+H _2O\rightarrow NaOH+H _2$

4. $Na+\dfrac12 H _2O\rightarrow NaOH+H _2$

Correct Option: A
Explanation:

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

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

When potassium is added to water, it burns with :

1. pink flame

2. blue flame

3. red flame

4. lilac flame

Correct Option: D
Explanation:

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

Potassium reacts with cold water and gives potassium hydroxide and hydrogen gas.

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

The reaction is so vigorous that the evolved hydrogen catches fire spontaneously.

Hence the correct option is D.

The colour of flame produced when a chunk of sodium comes in contact with water is :

1. pink

2. orange

3. yellow

4. purple

Correct Option: B
Explanation:

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

During the reaction, the sodium metal may well become so hot that it catches fire and burns with a characteristic orange colour.

Hence, the correct option is $B$.

A reddish brown colored element $X$ on heating in air, becomes a black colored compound $Y$.  The compound $X$ and $Y$ are :

1. $Cu, CuO$

2. $Pb, PbO$

3. $Fe, Fe _2O _3$

4. $Cr, Cr _2O _3$

Correct Option: A
Explanation:

$X$ 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.

$2Cu + O _{2} \rightarrow 2CuO$.
All other elements that are given are not black in colour

$Pb$ is grey in colour.
$Fe$ is silver-grey.
$Cr$ is steely-grey.

What is characteristics of solution when potassium reacts with water?

1. Colourless basic solution

2. Orange coloured basic solution

3. Yellowish basic solution

4. None of these

Correct Option: A
Explanation:

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

Which one of the following metals do not react with cold as well as hot water?

1. Na

2. Ca

3. Mg

4. Fe

Correct Option: D
Explanation:

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

Which of the following mixture on mixing with distilled water will make the water hard?

1. $Na _2SO _4+NaCl$

2. $NaNO _3+NH _4NO _3$

3. $MgSO _4+Na _2SO _4$

4. $KCl+NaCl$

Correct Option: C
Explanation:

Hard water is due to presence of $C{a^{2 + }}$ and $M{g^{2 + }}$.

So, option C is appropriate.

An alkali metal $A$ gives a compound $B$ (molecular mass $=40$) on reacting with water. The compound $B$ gives a soluble compound $C$ on treatment with aluminium oxide. Metal $A$ is:

1. $Al$

2. $K$

3. $Na$

4. $Mg$

Correct Option: C
Explanation:

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:
$Al _{2}O _{3} + 2NaOH \rightarrow 2NaAlO _{2} + H _{2}O$

Which of the following elements produces basic oxide on reacting with oxygen?

1. Chorium

2. Sulphur

3. Sodium

4. Magnesium

Correct Option: C,D
Explanation:

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.
$4Na + O _2 \rightarrow 2Na _2O$
$Na _2O + H _2O \rightarrow 2NaOH$
$2Mg + O _2 \rightarrow 2MgO$
$MgO + H _2O \rightarrow Mg(OH) _2$

When iron filings are heated in a steam of dry hydrogen chloride, the compound formed is $FeCl _{x}$, where 'x' is :

1. $1$

2. $2$

3. $3$

4. $4$

Correct Option: B
Explanation:

$Fe+2HCl\rightarrow Fe{ Cl } _{ 2 }+{ H } _{ 2\ }\\ x=2$

$Zn + H _{2}O$ (steam) $\longrightarrow A + B$

In the equation, A and B are :

1. $Zn$ and $H _2$

2. $ZnH _{2}$ and $O _{2}$

3. $ZnO _{2}$ and $H _{2}$

4. $ZnO$ and $H _{2}$

Correct Option: D
Explanation:

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

$Zn(s) +H _{2}O(g) \xrightarrow[\text{Above}\; 400^oC]{\Delta} ZnO(s)+H _2(g)$ .

Thus, the compounds A and B are $ZnO$ and $H _2$.

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