A 25.00-mL aliquot of a nitric acid solution of unknown concentration is pipetted into a 125-mL Erlenmeyer flask and 2 drops of phenolphthalein are added. The above sodium hydroxide solution (the titrant) is used to titrate the nitric acid solution (the analyte). If 12.75 mL of the titrant is dispensed from a burette in causing a color change of the phenolphthalein, what is the molar concentration of the nitric acid solution? (Show all calculations)

Ineed to find the answer of this question because i dont understand it

The content of manganese (mn) in steel was determined spectrophotometrically and with the use of the standard addition method. an unknown sample of mn from a digested steel sample gave an absorbance of 0.185 when analyzed spectrophotometrically. when 5.00 ml of solution containing 95.5 ppm mn was added to 50.0 ml of the unknown steel solution (digested sample), the absorbance was 0.248. calculate the concentration, in parts-per-million (ppm), of mn in the digested steel sample solution.

Phosgene (carbonyl chloride), cocl2, is an extremely toxic gas that is used in manufacturing certain dyes and plastics. phosgene can be produced by reacting carbon monoxide and chlorine gas at high temperatures: co(g) cl2(g)⇌cocl2(g) carbon monoxide and chlorine gas are allowed to react in a sealed vessel at 477 ∘c . at equilibrium, the concentrations were measured and the following results obtained: gas partial pressure (atm) co 0.830 cl2 1.30 cocl2 0.220 what is the equilibrium constant, kp, of this reaction