Molar Mass - SAT Subject Test in Chemistry

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Question

What is the approximate percentage of carbon by mass in heptane, which has the molecular formula $C_7H_{16}$ ?

Answer

First, calculate the molar mass of heptane, which is

$7(12\text{ amu}) + 16(1\text{ amu}) = 100\text{ amu or } \frac{\text{g}}{\text{mol}}$

We can calculate the percentage of carbon by mass in heptane by creating a fraction of the mass of carbon over the mass of the entire molecule and converting it into a percentage:

$\frac{\text{Mass of C in C}_7\text{H}_{16}}{\text{Mass of C}_7\text{H}_{16}}=\frac{7(12\text{ amu})}{100\text{ amu}}=\frac{84}{100}\times100%=84%\text{ C}$

For every 100 g of heptane, 84 g must come from carbon. This means that the percentage of carbon by mass is

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Question

What is the approximate percentage of carbon by mass in heptane, which has the molecular formula $C_7H_{16}$ ?

Answer

First, calculate the molar mass of heptane, which is

$7(12\text{ amu}) + 16(1\text{ amu}) = 100\text{ amu or } \frac{\text{g}}{\text{mol}}$

We can calculate the percentage of carbon by mass in heptane by creating a fraction of the mass of carbon over the mass of the entire molecule and converting it into a percentage:

$\frac{\text{Mass of C in C}_7\text{H}_{16}}{\text{Mass of C}_7\text{H}_{16}}=\frac{7(12\text{ amu})}{100\text{ amu}}=\frac{84}{100}\times100%=84%\text{ C}$

For every 100 g of heptane, 84 g must come from carbon. This means that the percentage of carbon by mass is

Compare your answer with the correct one above

Question

What is the approximate percentage of carbon by mass in heptane, which has the molecular formula $C_7H_{16}$ ?

Answer

First, calculate the molar mass of heptane, which is

$7(12\text{ amu}) + 16(1\text{ amu}) = 100\text{ amu or } \frac{\text{g}}{\text{mol}}$

We can calculate the percentage of carbon by mass in heptane by creating a fraction of the mass of carbon over the mass of the entire molecule and converting it into a percentage:

$\frac{\text{Mass of C in C}_7\text{H}_{16}}{\text{Mass of C}_7\text{H}_{16}}=\frac{7(12\text{ amu})}{100\text{ amu}}=\frac{84}{100}\times100%=84%\text{ C}$

For every 100 g of heptane, 84 g must come from carbon. This means that the percentage of carbon by mass is

Compare your answer with the correct one above

Question

What is the approximate percentage of carbon by mass in heptane, which has the molecular formula $C_7H_{16}$ ?

Answer

First, calculate the molar mass of heptane, which is

$7(12\text{ amu}) + 16(1\text{ amu}) = 100\text{ amu or } \frac{\text{g}}{\text{mol}}$

We can calculate the percentage of carbon by mass in heptane by creating a fraction of the mass of carbon over the mass of the entire molecule and converting it into a percentage:

$\frac{\text{Mass of C in C}_7\text{H}_{16}}{\text{Mass of C}_7\text{H}_{16}}=\frac{7(12\text{ amu})}{100\text{ amu}}=\frac{84}{100}\times100%=84%\text{ C}$

For every 100 g of heptane, 84 g must come from carbon. This means that the percentage of carbon by mass is

Compare your answer with the correct one above

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