Tag: chemistry

Questions Related to chemistry

Chromium hydroxide on reaction with excess $\displaystyle NaOH$ gives a soluble compound. Guess the colour of the compound :

action of alkalis on some metals and metal oxides analytical chemistry properties of acids and bases acids, bases and salts chemistry

  1. Dark green

  2. Dark blue

  3. Purple

  4. Pink

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Correct Option: A
Explanation:

Chromium hydroxide provide dark green solution with excess of NaOH.

Complete the following equation
$Pb\begin{pmatrix}OH\end{pmatrix} _2+NaOH\rightarrow$

action of alkalis on some metals and metal oxides analytical chemistry properties of acids and bases acids, bases and salts chemistry

  1. $Pb\begin{pmatrix}OH\end{pmatrix} _2+2NaOH\rightarrow Na _2PbO _2+2H _2O$

  2. $Pb\begin{pmatrix}OH\end{pmatrix} _2+NaOH\rightarrow2Na _2PbO _2+H _2O$

  3. $Pb\begin{pmatrix}OH\end{pmatrix} _2+2NaOH\rightarrow Na _2PbO _2+H _2O$

  4. $Pb\begin{pmatrix}OH\end{pmatrix} _2+NaOH\rightarrow Na _2PbO _2+2H _2O$

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Correct Option: A
Explanation:

$Pb\begin{pmatrix}OH\end{pmatrix} _2+2NaOH\rightarrow Na _2PbO _2+2H _2O$

Chromium hydroxide on reaction with excess $\displaystyle NaOH$ gives a soluble compound. Guess the molecular formula.

action of alkalis on some metals and metal oxides analytical chemistry properties of acids and bases acids, bases and salts chemistry

  1. $\displaystyle \left[ { Cr\left( OH \right) } _{ 3 } \right] $

  2. $\displaystyle { \left[ { Cr\left( OH \right) } _{ 4 } \right] }^{ - }$

  3. $\displaystyle { \left[ { Cr\left( OH \right) } _{ 5 } \right] }^{ 2- }$

  4. $\displaystyle { \left[ { Cr\left( OH \right) } _{ 6 } \right] }^{ 3- }$

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Correct Option: D
Explanation:

An excess of sodium hydroxide solution is added to a solution of the hexaaquachromium(III) ions to produce a solution of green hexahydroxochromate(III) ions.

$[Cr(H _2O) _6]^{3+} \xrightarrow{NaOH} [Cr(H _2O) _3(OH) _3] \xrightarrow{excess NaOH} [Cr(OH) _6]^{-3}$

The precipitate formed when NaOH reacts with zinc is :

action of alkalis on some metals and metal oxides analytical chemistry properties of acids and bases acids, bases and salts chemistry

  1. $Zn[OH] _{2}$

  2. ZnO

  3. $ZnH _{2}$

  4. $Na _{2}ZnO _{2}$

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Correct Option: D

In which of the following reactions hydrogen gas is liberated ?

chemistry study of the first element - hydrogen occurrence of hydrogen introduction to hydrogen hydrogen

  1. $C{H _3}COOH + Na$

  2. $C{H _3}COOH + NaHC{O _3}$

  3. $C{H _3}COOH + NaOH$

  4. $C{H _3}COOH + {H _2}O.$

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Correct Option: C

Brass gets discoloured in air because of the presence of which of the following gases in air  ?

chemistry study of the first element - hydrogen occurrence of hydrogen introduction to hydrogen hydrogen

  1.  Hydrogen sulphide

  2.  Oxygen

  3.  Nitrogen

  4. Carbon dioxide

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Correct Option: A
Explanation:

 Hydrogen sulphide

Metals like .......... , ........... and .......... give $H _2$ with steam.

chemistry study of the first element - hydrogen occurrence of hydrogen introduction to hydrogen hydrogen

  1. iron

  2. magnesium

  3. aluminium

  4. sodium

  5. calcium

  6. none of the above

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Correct Option: A,B,C
Explanation:

Metals which react with steam to give $H _2$ gas are Iron, Magnesium and Aluminium.


Magnesium ribbon reacts with steam to give Magnesium oxide and Hydrogen gas.

$Mg$ $+$ $H _2O$ $=$ $MgO$ $+$ $H _2$

Aluminium reacts with steam to give Aluminium Oxide and Hydrogen gas. But the reaction takes place very slowly, as a layer of Aluminium Oxide forms on the metal.

$2Al$ $+$ $3H _2O$ $=$ $Al _2O _3$ $+$ $3H _2$
Iron does not react with cold water. It reacts with steam to form Ferric Oxide and hydrogen gas.

$3Fe$ $+$ $4H _2O$ $=$ $Fe _3O _4$ $+$ $4H _2$
Thus, options A, B  and C are correct.

Sodium ________ reacts vigorously with cold water.

chemistry study of the first element - hydrogen occurrence of hydrogen introduction to hydrogen hydrogen

  1. metal

  2. amalgam

  3. in the molten state

  4. none of the above

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Correct Option: A
Explanation:

Sodium metal is an extremely reactive metal. When sodium metal comes into contact with water, it displaces hydrogen gas as follows:


$2 Na(s) + 2H _2O \rightarrow 2 NaOH(aq) + H _2(g)$

At $298 \, K$ , assuming ideal behaviour, the average kinetic energy of a deuterium molecule is :

chemistry study of the first element - hydrogen occurrence of hydrogen introduction to hydrogen hydrogen

  1. Two times that of a hydrogen molecule

  2. Four times that of a hydrogen molecule

  3. Half of that of a hydrogen molecule

  4. Same as that of a hydrogen molecule

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Correct Option: D
Explanation:

Average Kinetic Energy depends only on temperature

$\displaystyle (KE) _{avg} = \frac {3kT} {2} $ per molecule

Under suitable conditions, the following reaction:
Metal+Water $\xrightarrow [  ]{ Heat } $ Oxide or hydroxide of metal + Hydrogen 

may take place? Find which of the following metals, does not react in this way.

chemistry study of the first element - hydrogen occurrence of hydrogen introduction to hydrogen hydrogen

  1. Sodium

  2. Copper

  3. Iron

  4. Magnesium

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Correct Option: B
Explanation:

Because $Cu$ is placed below ${ H } _{ 2 }$ in reactivity series, hence cannot displace ${ H } _{ 2 }$. Hence reaction does not occur.