What dose it mean to say that mass is conserved during a physical change?

Isopropyl alcohol, (ch3)2choh, is a common solvent. determine the percent by mass of hydrogen in isopropyl alcohol. a) 6.71% h b) 13.4% h c) 25.0% h d) 53.3% h

Calculate the ph at the equivalence point for the titration of a solution containing 150.0 mg of ethylamine (c2h5nh2) with 0.1000 m hcl solution. the volume of the solution at the equivalence point is 250.0 ml. kb forethylamine is 4.7 × 10−4 .

If the solubility of a gas in water is 1.22 g/l at 2.75 atm, what is its solubility (in g/l) at 1.0 atm?