If the average molar mass of a sample of soybean oil is 1500 g/mol, how many grams of NaOH are needed to saponify 5.0 g of the oil?

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Welcome back everyone. A sample of coconut oil weighs around 8 g and has an average molecular weight of about 1200 g per mole. How many grams of potassium hydroxide will be needed to completely sify it. First of all, let's understand that saponification will take place with the triglyceride, right? So essentially what we want to do is to the general structure of a triglyceride which contains a three member chain with three oxygens. And those oxygens are going to be bonded to carbos, we're not interested in the actual structure. So we can just add R one, R two and R three as side chains bonded to each Coronel. Now, we are performing a reaction with potassium hydroxide and essentially it breaks the carbon oxygen bonds and we are forming Glycerol to begin with and carboxylate salts. That's the general equation. So first of all, we are going to draw glycerol and of course, there will be three carboxylate souls. Potassium is the counter ion for each an iron. So for the first side chain, we have R one for the cleavage of the other bond. We are going to have our two for the side chain. And now the third structure will be another car box late. We are three. And now, if we balance this equation, well, we need we most of potassium hydroxide because we are producing three carboxylate. So first of all, what we're going to do is identify the number of moles of triglyceride, let's call it T. So, NT means the number of moles of triglyceride. And we have to recall that we simply need to divide the mass of it by the molar mass. The mass given to us is 8 g and the molar mass is 1200 g per mole. When we divide the two numbers, we get 0.00667 moles, we only need one significant figure, but we want to avoid the propagation of error. So far, we can just use three significant figures. Now, from here, we can determine the number of moles of potassium hydroxide needed. And according to ST geometry, one mole of triglyceride needs three moles of potassium hydroxide. Meaning the number of moles of potassium hydroxide is three times as large. So we take the previous number and multiply it by three. Now, what do we get while we get 0.0 one? Basically, if we round properly, that'd be 0.02 zero. Since we need only one significant figure, it's OK to leave two. And therefore, if we want to identify the mass of potassium hydroxide, let's recall that mass equals the number of moles multiplied by the molar mass. The number of moles would be 0.020 moles. And the molar mass in at least two significant figures would be 56 g per mol for potassium hydroxide using the periodic table. And when we multiply those numbers, we have to recall that we only need one significant figure. So we get 1 g and that would be our final answer to this problem. Thank you for watching.

If the average molar mass of a sample of soybean oil is 1500 g/mol, how many grams of NaOH are needed to saponify 5.0 g of the oil?

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Key Concepts

Saponification

Stoichiometry

Molar Mass