36. Solving a chemistry problem

10. a) How many g of HNO3 is contained in 1 dm3 of a solution if 18.98 cm3 of a NaOH solution with a molar concentration of 0.0500 mol/dm3 (K = 1.0181) is consumed to titrate 20.00 cm3 of it?
b) Nitrogen from permanently 0.8899 organic matter is converted into ammonium salt. After boiling with concentrated alkali, ammonia was isolated and 20.00 cm3 of hydrochloric acid with a molar equivalent concentration of 0.2230 mol/dm3 was absorbed. The acid that did not react with ammonia was titrated with 16.20 cm3 of sodium hydroxide solution with a titer of 0.002720 g/cm3. Calculate the mass fraction of nitrogen in organic matter.