Final answer:
The calculation involves first determining the mass of t-pentyl alcohol from its given volume and density and then calculating the moles by dividing by its molecular weight. The correctly rounded result is 0.046 moles of t-pentyl alcohol.
Step-by-step explanation:
The student asked about the number of moles of t-pentyl alcohol present in 5.0 ml of the substance (2-methyl-2-butanol).
To answer this, we must first know the density of t-pentyl alcohol, which is approximately 0.810 g/ml.
Next, we calculate the mass by multiplying the volume (5.0 ml) by the density (0.810 g/ml), giving us 4.05 g (5.0 ml x 0.810 g/ml).
The molecular weight of t-pentyl alcohol is around 88.15 g/mol.
So, the number of moles is calculated by dividing the mass by the molecular weight, which results in approximately 0.0459 moles (4.05 g / 88.15 g/mol).
When rounding to the correct number of significant figures (three, since the volume was given to two decimal places and is the limiting measure), the answer is 0.046 moles of t-pentyl alcohol.