1. Cetyl palmitate (C32H64O2) is a waxy solid and is the main component of spermaceti, the once prized wax found in the skull of sperm wales. The heads of sperm whales can contain up to 1900 L of spermaceti. If the most famous sperm whale, Moby Dick, had a head containing 1514 L of spermaceti, consisting of 77.3% (by mass) cetyl palmitate, how many kL of liquid water would be produced from the combustion of the cetyl palmitate? Assume there is excess oxygen and the reaction proceeds in a 68.2% yield. The density of spermaceti is 828.4 kg/m^3

  2. Zinc metal can be dissolved in nitric acid (it actually reacts with the nitric acid to produce hydrogen gas and soluble zinc nitrate). If a solution of nitric acid contains 2.6 mol nitric acid per liter of solution, how many mL of solution are needed to completely dissolve a piece of zinc metal that is 1.32 in wide, 4.66 in long and 0.436 mm thick? The density of zinc is 7.14 g/mL

  3. When zinc metal is placed in an aqueous solution of copper(II) sulfate, the zinc is oxidized and goes into the solution as zinc ions. At the same time, the copper is reduced to copper metal and deposits onto the zinc metal. In effect, the zinc metal is slowly "dissolving" and being coated with copper metal at the same time. A 1939.2 g strip of zinc metal is placed into a solution containing an excess of copper(II) sulfate and after some time has elapsed it is pulled out and its mass is determined to be 1927.3 g. What mass of zinc metal was oxidized?

  • $\begingroup$ Homework! Please show your own attempt at a solution, and describe what difficulty you have. We're not a free homework service. $\endgroup$ – Karl Jul 14 '18 at 5:55
  • $\begingroup$ Hi Naomi, welcome to Chem.SE! We require you to show your efforts on this problem. What formulae/steps did you try? Where did you get stuck? Please add this to your question. Thanks! $\endgroup$ – Gaurang Tandon Jul 14 '18 at 7:25
  • $\begingroup$ @Gaurang Tandon I first have to balance the equations first. then convert my units. After that im not sure what the steps are called. The notes i have taken in my Chemistry class only help with non-lengthy questions, so the structure of these questions generally confuse me. $\endgroup$ – Naomi Jul 15 '18 at 2:40
  • $\begingroup$ Also i came on this site for help. not for "free homework service" @Karl . that's why i asked for the steps so i could follow them on dozens of other assignments i was given. $\endgroup$ – Naomi Jul 15 '18 at 2:40

It often helps to

  1. ask yourself: What are they actually asking for?
  2. reorder the information given in the question.

Let's try this for the first question:

Apparently, this is about cetyl palmitate ($\ce{C32H64O2}$). When the compound is burned in excess of oxygen, carbon dioxide ($\ce{CO2}$) and water ($\ce{H2O}$) are produced. It's your task to calculate the amount of water generated upon burning a certain amount of cetyl palmitate.

  • Do you remember the concept of the unit mole? How many molecules of water can be formed from a molecule of cetyl palmitate that contains 64 hydrogen atoms? Knowing the number of molecules and the molecular mass of a compound gives the corresponding weight.

If the initial amount of cetyl palmitate was given in moles you'd be done. Obviously, that's too easy.

Instead, the Moby Dick example was given. This adds two other concepts:

  • density, which correlates mass and volume
  • percentages: if only x% of your starting is usable, what is the actual amount work with in further calculations?

Let this sink in for a while and then give it a try. You can do this by yourself!

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