Which resource is the best for information about current events? biography encyclopedia newspaper

Which of the following is a compound? a.carbon b.oxygen c.hydrogen d.water

The following reaction shows sodium carbonate reacting with calcium hydroxide. na2co3 + ca(oh)2 → naoh + caco3 how many grams of naoh are produced from 20.0 grams of na2co3? (molar mass of na = 22.989 g/mol, c = 12.01 g/mol, o = 15.999 g/mol, ca = 40.078 g/mol, h = 1.008 g/mol) 12.2 grams 15.1 grams 24.4 grams 30.2 grams

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.