The diagram below shows a section of a 50.00 mL burette containing a colourless solution.

The reading indicated on the burette is closest to
A. 14.50
B. 14.58
C. 15.42
D. 15.50

Solution

Serotonin (C₁₀H₁₂N₂O; molar mass = 176 / mol) is a compound that conducts nerve impulses in the brain and muscles. A sample of spinal fl uid from a volunteer in a study was found to contain a serotonin concentration of 1.5 ng/ L (1.5 nanograms per litre).
How many molecules of serotonin are there in one millilitre of the spinal fl uid?
A. 5.13 × 10⁹
B. 9.03 × 10¹¹
C. 5.13 × 10²⁷
D. 9.03 × 10²⁹

Solution.

Xylose is a compound that has five carbon atoms in each molecule and contains 40% carbon by mass.
What is the molar mass of xylose?
A. 30
B. 67
C. 150
D. It cannot be determined without further information.

Solution