Question

mass and atoms quick check
a scientist uses 3 g of water (h₂o) in an experiment. which option describes the first step in calculating the number of molecules in 3 g of water? (1 point)
identify the molar masses of h and o.
calculate the number of moles of water
determine the molar mass of water.
apply avogadros number, 6.022 × 10²³

Explanation:

To calculate the number of molecules in a given mass of a substance (water here), the general formula is \(n=\frac{m}{M}\) (where \(n\) is the number of moles, \(m\) is the mass, and \(M\) is the molar mass) and then \(N = n\times N_A\) (where \(N\) is the number of molecules and \(N_A\) is Avogadro's number). First, we need to know the molar mass of the substance (water). To find the molar mass of water (\(H_2O\)), we use the molar masses of its constituent elements (\(H\) and \(O\)). So, the first step is to determine the molar mass of water.

Answer:

Determine the molar mass of water.