In (i) $${H_2}{O_2}$$ reduces $$KMn{O_4}$$ to $$MnS{O_4}$$ and is oxidised to $${O_2}.$$
In (ii) $${H_2}{O_2}$$ oxidises $$Cr{\left( {OH} \right)_3}$$ to $$N{a_2}Cr{O_4}$$ and is reduced to $${H_2}O.$$
Water is reduced to dihydrogen by highly electropositive metals. In this reaction $${H_2}O$$ is reduced to $${H_2}.$$ In other two reactions, $${H_2}O$$ is oxidised to $${O_2}$$ and $${P_4}{O_{10}}$$ is hydrolysed by water.
65.
Which of the following metal evolves hydrogen on reaction with cold dilute $$HN{O_3}?$$
$$Na$$ reacts with cold water, $$Mg$$ reacts with hot water, $$Fe$$ reacts with steam and $$Au$$ does not react with water.
$$3Fe + \mathop {4{H_2}O}\limits_{\left( {{\text{steam}}} \right)} \to F{e_3}{O_4} + 4{H_2} \uparrow $$
67.
Which is not a property of water?
A
It is a colourless and tasteless liquid.
B
There is no hydrogen bonding in solid state of water.
C
It is an excellent solvent for transportation of ions in plants and animals.
D
Ice is lighter than liquid water.
Answer :
There is no hydrogen bonding in solid state of water.
Strength of the solution $$ = 34\,g/L$$
$$1\,L$$ of the solution contains $$34\,g$$ of $${H_2}{O_2}$$
$$200\,mL$$ of the solution contains $$\frac{{34}}{{1000}} \times 200 = 6.8\,g$$ of $${H_2}{O_2}$$
$$\mathop {2{H_2}{O_2}}\limits_{2 \times 34\,g} \to 2{H_2}O + \mathop {{O_2}}\limits_{32\,g} $$
$$68\,g$$ of $${H_2}{O_2}$$ gives $$32\,g$$ of $${O_2}$$
$$6.8\,g$$ of $${H_2}{O_2}$$ gives $$ = \frac{{32}}{{68}} \times 6.8 = 3.2\,g$$ of $${O_2}$$
70.
Which of the following reactions increases production of dihydrogen from synthesis gas?
A
\[C{{H}_{4\left( g \right)}}+{{H}_{2}}{{O}_{\left( g \right)}}\xrightarrow[Ni]{1270\,K}C{{O}_{\left( g \right)}}+3{{H}_{2\left( g \right)}}\]
B
\[{{C}_{\left( s \right)}}+{{H}_{2}}{{O}_{\left( g \right)}}\xrightarrow{1270\,K}C{{O}_{\left( g \right)}}+{{H}_{2\left( g \right)}}\]
C
\[C{{O}_{\left( g \right)}}+{{H}_{2}}{{O}_{\left( g \right)}}\xrightarrow[\text{Catalyst}]{673\,K}\] \[C{{O}_{2\left( g \right)}}+{{H}_{2\left( g \right)}}\]
D
\[{{C}_{2}}{{H}_{6\left( g \right)}}+2{{H}_{2\left( g \right)}}O\xrightarrow[Ni]{1270\,K}\] \[2C{{O}_{\left( g \right)}}+5{{H}_{2\left( g \right)}}\]
Answer :
\[C{{O}_{\left( g \right)}}+{{H}_{2}}{{O}_{\left( g \right)}}\xrightarrow[\text{Catalyst}]{673\,K}\] \[C{{O}_{2\left( g \right)}}+{{H}_{2\left( g \right)}}\]
The production of dihydrogen can be increased by reacting carbon monoxide of syngas mixtures with steam in the presence of iron chromate as catalyst.
\[C{{O}_{\left( g \right)}}+{{H}_{2}}{{O}_{\left( g \right)}}\xrightarrow[\text{Catalyst}]{673\,K}\] \[C{{O}_{2\left( g \right)}}+{{H}_{2\left( g \right)}}\]
This is called water - gas shift reaction.