Which of the following can only be separated into two or more pure substances by a chemical change?
a. an element
b. a compound
c. a homogeneous mixture
d. a heterogeneous mixture

4nh3+5o2--> 4no+6h20what is the total number of moles of h2o produced when 12 mole of nh3 is completely consumed?

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.

Which statement describes the phase change that occurs when dry ice is placed in an open container at room temperature?