Baking powder is the ingredient missing.
The baking powder used for baking cake consists of sodium bicarbonate(NaHCO3) and small amount of tartaric acid[COOH-CH(OH)-CH(OH)-COOH]. The baking powder will give soft and spongy texture to the cake but also give bitter taste. The tartaric acid neutralises the bitterness produced by baking powder.
NaHCOā3 + H+(from tartaric acid)------->Na+ + CO2 + H2O
The carbon-dioxide produced allows the cake to rise and makes it soft and spongy.