How many molecules are in 7.5 mol of h2o

A mole refers to 6.022⋅1023 items. H2O has 2 hydrogen atoms and 1 oxygen atom...so a total of 3 atoms in each H2O.

Therefore (6.022⋅1023)⋅ (3 atoms) =18.066⋅1023

Then we need to change the answer into proper scientific notation:
18.066⋅1023=1.8066⋅1024

Lastly, change to the proper number of significant figures. There are 4 significant figures in 6.022. Due to this we need to also have 4 significant figures in the final answer, so we would round 1.8066⋅1024→1.807⋅1024

So, your final answer is 1.807⋅1024 for one mole of h2o. multiply that by 7 and your answer is 13.55 * 1024 

1. 1 mole of anything contains 6.022x10^23 pieces  

d  

2. a  

3. c, number  

5. 1.24x10^24atoms / 6.022x10^23atoms/mole = 2moles h2 atoms  

6. fe2br3 mass = 2moles x mass fe + 3 moles x mass br  

molar mass = grams / number of moles = g/mole  

to find moles = g / molar mass  

to find mass = g = molar mass / moles