To find the number of moles of ethanol (CH₃CH₂OH) in a sample weighing 45 g, we first need to calculate the molar mass of ethanol.
Step 1: Calculate the molar mass of ethanol (CH₃CH₂OH)
The molar mass of ethanol can be calculated by adding up the molar masses of all the atoms in the formula:
- Carbon (C): 2 atoms × 12.01 g/mol = 24.02 g/mol
- Hydrogen (H): 6 atoms × 1.01 g/mol = 6.06 g/mol (since there are 5 from CH₃CH₂ and 1 from OH)
- Oxygen (O): 1 atom × 16.00 g/mol = 16.00 g/mol
Now, add them all together:
\[ \text{Molar mass of CH₃CH₂OH} = 24.02 , \text{g/mol} + 6.06 , \text{g/mol} + 16.00 , \text{g/mol} = 46.08 , \text{g/mol} \]
Step 2: Calculate the number of moles of ethanol
To find the number of moles, we use the formula:
\[ \text{Number of moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}} \]
Now substituting the values:
\[ \text{Number of moles} = \frac{45 , \text{g}}{46.08 , \text{g/mol}} \]
Calculating this gives:
\[ \text{Number of moles} \approx 0.975 , \text{mol} \]
Final Answer:
The chemist will use approximately 0.975 moles of ethanol.