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Allen B.
USC Student--Chemistry Enthusiast and Native Chinese Speaker
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Mandarin
TutorMe
Question:

Fill in the blank for the following sentence. 你明天要去哪裡？ A. 謝謝 B. 明天見 C. 太好了 D. 北京

Allen B.

The answer is D as the other options are illogical and are not nouns.

Chemistry
TutorMe
Question:

The organic molecule Glyoxal contains 55.14% oxygen and 3.47% hydrogen. If the molar mass of the molecule is 58.04 g/mol, find its molecular formula.

Allen B.

The first step in questions that ask for molecular formulas is to determine the percentage of each atom in the molecule. While the problem does not explicitly say that it contains carbon, we know that it does because it's an organic molecule, as stated in the beginning. Knowing this, we can find the mass percent of carbon simply by subtracting the percentages of oxygen and hydrogen from 100% to get 41.39%. Next, we assume that what we have at hand weighs 100 grams. Multiply 100 grams by the percentages of the atoms to get the mass of each individual atom. So we have 55.14 grams of oxygen, 41.39 grams of carbon, and 3.47 grams of hydrogen. Next, we need to find the moles of the individual atoms by dividing by their molar masses. $$\frac{55.14g O}{16.00g/mol} = 3.446 mol O$$ $$\frac{41.39g C}{12.01g/mol} = 3.446 mol C$$ $$\frac{3.47g H}{1.008g/mol} = 3.442 mol H$$ After this, we take the least moles out of the atoms and divide them all by that mol. In this case, it's hydrogen. We get the moles to be about 1 for each atom. This gives us the empirical formula of: CHO To get the molecular formula, divide the given molecular mass by the molecular mass of your calculated empirical formula. The empirical formula of CHO is: 29.018 g/mol so we divide the molecular mass of Glyoxal to get the molecular formula coefficient. $$\frac{58.04g/mol}{29.018g/mol} = 2$$ We then multiply this number to the empirical formula to get the molecular formula. $${C_2H_2O_2}$$

Basic Chemistry
TutorMe
Question:

Name the following: $${H_2S}$$ $${H_2SO_4}$$ $${HF}$$ $${Na_3PO_4}$$

Allen B.

For $${H_2S}$$: Hydrogen Sulfide. This is because the molecule is an ionic bond so you take the name of the anion and combine it with the name plus root (-ide) of the anion. $${H_2SO_4}$$ Sulfuric Acid. This is because there is an oxygen present in the anion, so you have either the choice of using the root ous or ic. Because the anion is sulfate, with the root ate, you replace the ate with ic to get your answer. You know this is an acid because H is present as the cation. $${HF}$$ Hydrofluoric Acid. Because this does not contain any oxygen in the anion, we must add a hydro in the beginning and replace the last few letters of fluorine with ic.

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