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

answer : one can design an experiment using a liquid and an additive that can be added to the liquid and observe the chemical changes in the reaction species.

one would need a beaker which is filled with a known amount of the liquid in which thermometer is placed to measure the temperature changes; after addition of the additive to the liquid solution one can note down the temperature change and find whether the reaction is endothermic or exothermic in nature. by subtracting the initial temperature value with the final temperature one can find the temperature changes.

various combinations of liquid and additive can be used. liquid in this case can be a known quantity of water and additives can be epsom salt or without epsom salt the experiment can be conducted to notice the changes. water and ice, hydrogen peroxide and dry yeast, vinegar and baking soda,etc.