level: General
Questions and Answers List
level questions: General
| Question | Answer |
|---|---|
| A substance, A2B, has the composition by mass of 60% A and 40% B. What is the composition of AB2 by mass? A) 40% A, 60% B B) 50% A, 50% B C) 27% A, 73% B D) 33% A, 67% B E) none of these | ANS: C Use an arbitrary mass, 100 g is an easy number to work with. 60% of 100 g is 60 g, there are two A's. Each A is 30 g 40 g is B, and there is only one, so B is 40 g. AB2, would have a mass of 30 g + 2*40 g = 110 g The new percent by mass composition of A is: 30g110g∗100%=27.3% The new percent by mass composition of B is: 80g110g∗100%=72.7% |
| Indium reacts with chlorine to form InCl3. In the balanced equation for this reaction, the coefficient of the indium trichloride is A) 1 B) 2 C) 3 D) 4 E) 6 | B 2In + 3Cl2 → 2InCl3 |
| You heat 3.869 g of a mixture of Fe3O4 and FeO to form 4.141 g Fe2O3. The mass of oxygen reacted is A) 0.272 g B) 0.476 g C) 1.242 g D) 1.000 g E) none of these | A Your original mixture contains iron(II, III) oxide, Fe3O4, and iron(II) oxide, FeO, in some unknown proportion. After you heat this mixture, it will react with the oxygen in the air to produce iron(III) oxide, Fe2O3. Notice that the mass of the mixture increases from 3.869 g to 4.141 g. So what causes this increase in mass? The amount of oxygen the react with the initial mixture to form the iron(III) oxide! This means that the mass of oxygen that reacted will be equal to the difference between the final mass and the initial mass of the mixture mFe2O3=mmixture+moxygen moxygen=mFe2O3−mmixture moxygen=4.141 g−3.869 g=0.272 g https://socratic.org/questions/5612eb9f581e2a39ce51b7c6 |