Question

An NaOH molecule has a mass of 40.00 atomic mass units (amu). Which of the following statements is true?

A) An NaOH molecule has a molar mass of 40.00 amu.

B) The combined mass of 6.022 x 1023 NaOH molecules is 40.00 amu.

C) A sample of NaOH with a mass of 40.00 amu contains 1.00 mol of NaOH.

D) The combined mass of 6.022 x 1023 NaOH molecules is 40.00 g.

Answer 1

(D)

Step-by-step explanation:

By definition, an atomic mass unit is defined as a mass equal to one twelfth the mass of an atom of carbon-12 isotope. The mass of any isotope of any element is expressed in relation to the carbon-12 standard. In this question, the mass of an NaOH molecule is equal to 40.00 amu.

The mass of one mole of a substance is equal to its molecular weight. For example, the mean molecular weight of water is 18.015 amu, so one mole of water weighs 18.015 grams.

One mole of a substance is equal to 6.022 × 10²³ units of that substance (such as atoms, molecules, or ions).

=> One mole of NaOH, which is equal to 6.022 × 10²³ molecules of NaOH, weighs 40.00 g. Hence, (D) is correct.

(A) is wrong because the units of molar mass are in g/mol and not amu.

(B) is wrong because mass is mentioned in amu for Avogadro number of molecules and not grams.

(C) is wrong because the mass of a sample is not in amu but in grams.