If the concentration of glucose (C₆H₁₂O₆) in blood is 0.72 g L⁻¹, the molarity of glucose in blood is ____________ × 10⁻³ M. (Nearest integer)
[Given : Atomic mass of C = 12, H = 1, O = 16 u]

Solution

Chemistry ma’am · 3 steps

Grams per litre into moles per litre: just divide by glucose's molar mass.

1. Molar mass. For C₆H₁₂O₆: 6 × 12 + 12 × 1 + 6 × 16 = 72 + 12 + 96 = 180 g mol⁻¹.
2. Why divide. Molarity is moles of solute per litre. The blood already has 0.72 g in every litre, so turning those grams into moles gives the molarity directly.

   M = (0.72 g L⁻¹)/(180 g mol⁻¹) = 0.004 mol L⁻¹ = 4 × 10⁻³ M

3. So. The molarity of glucose in blood is 4 × 10⁻³ M, so the blank is 4.

The common slip: 0.004. Writing the full molarity 0.004 in the blank gives the wrong entry. The question has already pulled out 10⁻³, so only the 4 goes in.

The idea to keep. Whenever a concentration is given in g/L, molarity is just that number divided by the molar mass. Check the power of ten the blank asks for before you write the answer.

Answer from the NTA final answer key. Solution by PrepWiser.