a student conducted the gas law reaction between mg metal and hcl as demonstrated for class, but he forgot to record the starting mass of magnesium he used. his instructor told him to use the theoretical ideal gas constant to work backwards to figure out this mass. the atmospheric pressure at the time of the experiment was 767.11 mm hg. the student noticed that he obtained 42.54 ml of h2 gas at 22.06oc. he calculated the pressure caused by the liquid level difference to be 13.27 mm hg.