The following was taken from my worksheet: "What volume of hydrogen gas, measured at STP, can be released by 42.7 grams of zinc metal as it reacts with hydrochloric acid?" I would like an explanation of the steps, without outright giving me the answer. Thanks!

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What mass of natural gas (ch4) must you burn to emit 276 kj of heat?

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.