Given :
Mass of urea = 250 g,
Cost for 250 g glucose = Rs 40,
Molecular formula of glucose = C6H12O6
To find : Cost per mole of glucose.
Calculation : Molecular formula of glucose is (C6H12O6).
Molecular mass of glucose
= (6 × Average atomic mass of C) + (12 × Average atomic mass of H) + (6 × Average atomic mass of O)
= (6 × 12 u) + (12 × 1 u) + (6 × 16 u)
= 180 u
∴ Molar mass of glucose = 180 g mol-1
Number of moles = \(\frac{Mass\,of\,a\,subtance}{Molar\,mass\,of\,a\,subtance}\)
= \(\frac{250\,g}{180\,g\,mol^{-1}}\)
= \(\frac{250}{180}\) mol
Now,
\(\frac{250}{180}\) mol of glucose cost = Rs 40
1 mol glucose cost = x
∴ x = \(\frac{40\times 180}{250}\)
= Rs 28.8/mol of glucose
∴ The cost of glucose per mole is Rs 28.8.
[Calculation using log table :
\(\frac{40\times 180}{250}\)
= Antilog10[log10(40) + log10(180) + log10(250)]
= Antilog10[1.6021 + 2.2553 – 2.3979]
= Antilog10[1.4595]
= 28.80]