Weegy: Magnesium Hydroxide. User: no you said the same as mg + water Weegy: Mg and HCl react together to give MgCl and H2 gas which is released in effervescence concentration increases the rate of reaction because there are more molecules of the acid to react with the magnesium, [ however it does not increase the total volume of hydrogen gas released because there is a limited mass of magnesium which will react. If you are doing a level then try comparing mono and dibasic acids eg, Hcl and H2SO4 and H2SO4 should be nearly double as fast because of hydrogen ions, however ou need to take surface area of Mg into account. [www.finishing.com/110/55.shtml] ] (More)