Which of the following is NOT a sign of a chemical change? Mixing two white powders in water and the resulting mixture turns red in color.
Steam collecting on the lid of a pot of boiling water.
Cracking a light stick which starts to glow.
a
Putting drops of water on calcium carbonate and watching bubbles appear.

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.