Question

Question #f137a

Answer 1

`=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%`