8. a volume of 7.5 l of hydrogen gas at stp was produced from the single-replacement
reaction of zinc with nitric acid. calculate the mass of zinc needed for this reaction.

20.60 g

We are given;

Required to determine the mass of zinc needed for the reaction.

Zn(s) + 2HNO₃(aq) → Zn(NOₐ)₂ + H₂(g)

we know that 1 mole of a gas occupies 22.4 L at STP

Moles of Hydrogen = 7.05 L ÷ 22.4 L/mol

                                 = 0.315 moles

Then, we determine the number of moles of Zinc that reacted

Therefore,

Moles of Zinc = Moles of Hydrogen

Hence;

Mass of Zinc = 0.315 moles × 65.38 g/mol

                     = 20.60 g

Thus, the mass of zinc that reacted 20.60 g

your picture is not part of the scientific method.

the leaf is an organ of a typical plant, and the main functions are to complete photosynthesis and allow the plant to exchange gas, just like how we have the respiratory system. leaves have the stomata, which collects maintains co2 and o2 levels. this is necessary for cell metabolism. the leaf also collects sunlight using chloroplasts. succinctly, leaves own a pivotal role in sustaining plant life.