Answer to Question #104392 in Chemistry for Monse

Question

High concentrations of ammonia (NH3), nitrite ion and nitrate ion in water can kill fish. Lethal concentration of these species for rainbow trout are 1.1 mg/L, 0.40 mg/L, and 1361 mg/L, respectively. Express these concentrations in molality units, assuming a solution density of 1.00 g/mL.

Answer 1

Molecular weight of ammonia is 17.031 g/mol.

Molar concentration is defined by the following formula:

M = n / V

where M - molarity, n - number of moles, V - volume.

As n = m / Mr (m - mass, Mr - molecular weight, Mr(NH₃) = 17.031 g/mol), the molar concentrations are:

M₁ = 1.1 mg / 1 L = 1.1 g × 10^-3 / (17.031 g/mol × 1 L) = 0.065 × 10^-3 mol/L = 65 µmol/L = 65 µM

M₂ = 0.40 mg / 1 L = 0.40 g × 10^-3 / (17.031 g/mol × 1 L) = 0.024 × 10^-3 mol/L = 24 µmol/L = 24 µM

M₃ = 1361 mg / 1 L = 1361 g × 10^-3 / (17.031 g/mol × 1 L) = 79.9 × 10^-3 mol/L = 79.9 mmol/L = 79.9 mM

Answer: 65 µM, 24 µM, 79.9 mM.