Question #f137a

1 Answer
P dilip_k
Jul 9, 2016

#=79%#

Explanation:

On heating the given mixture of 100g of #NaHCO_3 and Na_2CO_3# ,only# NaHCO_3# will decompose according to the following balanced equation but other component #Na_2CO_3# will not.

The Equation

#2NaHCO_3(s)->Na_2CO_3(s)+CO_2(g)+H_2O(g)#

According to this balanced equation 2 moles of solid #NaHCO_3# produces 1 mole of #H_2O(g) #and 1 mole of #CO_2(g)# as volatile matter

Molar mass of
#NaHCO_3 =23+1+12+3*16=84g/"mol"#

Molar mass of
#CO_2=12+2*16=44g/"mol"#

Molar mass of #H_2O=2*1+16=18g/"mol"#

By the problem the decrease in mass = initial mass -residual mass= =0.31g

According to the decomposition reaction total 44+18=62g decrease in mass occurs for presence of #2*84g=168g# of #NaHCO_3# in the mixture.

So decrease in mass of 0.31 g will occur for the presence of

#(168*0.31)/62g=0.84g" "NaHCO_3#
in the given mixture

So the amount#Na_2CO_3=4-0.84=3.16g# in 4g mixture

So percentage of #Na_2CO_3 =3.16/4xx100%=79%#

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