Tag: chemistry

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.

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.
$\displaystyle KOH \rightarrow K^+ + OH^-$

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

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 $

97.8 C = 370.95 Kelvin = 208.04 Fahrenheit.

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.