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Molecular mass is the mass of a single molecule Molar mass refers to the mass of 1 mole of molecules, ie $ 6.023 × 10^{23}$ of them. Eg: Molecular mass of $\ce{H2}$ is about $3.32 \times 10 ^{-24}\ \mathrm g$ or about $2\ \mathrm u$. Here "$\mathrm u$" is just a unit, $1\ \mathrm u = 1.66 \times 10^{-24}\ \mathrm g$ Whereas molar mass is about $2\ \...


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Let's look at the $\ce{^9_4Be}$ isotope and apply the definitions: Relative atomic mass The relative atomic mass of $\ce{^{12}C}$ is, by definition, 12. Looking at the periodic table, we find that the relative atomic mass of beryllium is 9.0121831(5). That makes sense because $\ce{^{12}C}$ has a mass number of 12 (6 protons and 6 neutrons) while beryllium ...


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It is the same reason that a dozen doesn't depend on whether you are counting grapes or elephants. That is how the mole is defined: it is a number, nothing else. The confusion, I suspect, is because of how we measure that number (or, strictly, how we originally measured it as the definition changed recently). The intention of the unit was always to define a ...


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I agree with the starting point of the Matthew's solution, namely the definition of vapor density, but I fail to understand the follow-up math, so I just post my approach. $$M(\ce{ECl_x}) = D\cdot M(\ce{H2}) = 85\cdot\pu{2 g mol-1} = \pu{170 g mol-1}\tag{1}$$ By definition, molar mass $M(\ce{ECl_x})$ is also $$M(\ce{ECl_x}) = M(\ce{E}) + x\cdot M(\ce{Cl})$...


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