How many atoms are represented by one formula unit of aluminum chromate, Al2(CrO4)3

17 atoms

Explanation:

If what we want is to calculate the number of atoms. We must take into account the subscripts of the formula. We can rewrite the formula  taking into account the "ones" implicit in the formula, therefore we will have:

Now we have a "3" outside the parenthesis. Therefore, we must multiply this 3 by the number of atoms within the parentheses:

-) Oxygen atoms: 4 x 3 = 12 atoms

-) Chromium atoms: 1 x 3 = 3 atoms.

If we take into account we have 2 aluminum atoms, in total, we will have:

-) 12 oxygen atoms

-) 3 chromium atoms

-) 2 aluminum atoms

12 + 3 + 2 = 17 atoms

In total, we will have 17 atoms.

See figure 1

I hope it helps!

given:

mass of na = 115 g

excess cl2

to determine:

mass of nacl produced

explanation:

given reaction is-

2na(s) + cl2(g) → 2nacl(s)

since cl2 is in excess, na will be the limiting reagent

as per the reaction stoichiometry na: nacl = 1: 1

i.e. moles of na reacted = moles of nacl formed

now, # moles of na = mass of na/atomic mass

                                  = 115 g/23 g.mol-1 = 5 moles

therefore, moles of nacl = 5

molar mass of nacl = 58 g/mol

mass of nacl = 5 moles * 58 g.mol-1 = 290 g

ans: amount of nacl produced = 290 g