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how do you calculate the % by mass of Na2CO3 washing soda?
2.7g of washing soda (Na2CO3) sample was treated with 25cm^3 of 1moldm^-3 H2SO4 solution(in excess) & the reaction mixture was boiled. If 20 cm^3 of 1moldm^-3 KOH solution was used to neutralize this remaining solution.calculate the % by mass of Na2CO3 in the sample of washing soda.
i'm a little bit confused about the reactions occuring in the presence of KOH, please can somebody explain this?
actually it should be the % by mass of Na2CO3 IN washing soda
1 Answer
- Roger the MoleLv 77 years agoFavorite Answer
The KOH is reacting with the excess H2SO4:
2 KOH + H2SO4 → K2SO4 + 2 H2O
(0.020 dm^3) x (1 mol/dm^3 KOH) x (1 mol H2SO4 / 2 mol KOH) = 0.010 mol H2SO4 in excess
((0.025 dm^3) x (1 mol/dm^3 H2SO4)) - (0.010 mol H2SO4 excess) =
0.015 mol H2SO4 reacted with Na2CO3
Na2CO3 + H2SO4 → Na2SO4 + H2O + CO2
Supposing no other component of the original washing soda mixture reacts with H2SO4:
(0.015 mol H2SO4) x (1 mol Na2CO3 / 1 mol H2SO4) x (105.98861 g Na2CO3/mol) / (2.7 g) = 0.5888 =
59% Na2CO3 by mass
