Calculate (to the nearest 0.1 u) the formula mass of these compounds.

(a) rubidium nitrate, RbNO3
u

(b) aluminum peroxide, Al2(O2)3
u

(c) water, H2O
u

To calculate the formula mass of a compound, you need to determine the atomic masses of each element present in the compound and the number of atoms of each element.

(a) Rubidium Nitrate, RbNO3:
To calculate the formula mass of rubidium nitrate, you need to determine the atomic masses of rubidium (Rb), nitrogen (N), and oxygen (O). The molecular formula RbNO3 indicates that there is 1 rubidium atom, 1 nitrogen atom, and 3 oxygen atoms.

Atomic masses:
- Rubidium (Rb): 85.47 u (rounded to two decimal places)
- Nitrogen (N): 14.01 u
- Oxygen (O): 16.00 u

Calculating the formula mass:
Formula mass = (Number of rubidium atoms x Atomic mass of rubidium) + (Number of nitrogen atoms x Atomic mass of nitrogen) + (Number of oxygen atoms x Atomic mass of oxygen)

Plugging in the values:
Formula mass = (1 x 85.47) + (1 x 14.01) + (3 x 16.00)
Formula mass = 85.47 + 14.01 + 48.00
Formula mass = 147.48 u (rounded to one decimal place)

Therefore, the formula mass of rubidium nitrate (RbNO3) is approximately 147.5 u.

(b) Aluminum Peroxide, Al2(O2)3:
To calculate the formula mass of aluminum peroxide, you need to determine the atomic mass of aluminum (Al) and oxygen (O). The molecular formula Al2(O2)3 indicates that there are 2 aluminum atoms and 3 oxygen atoms.

Atomic masses:
- Aluminum (Al): 26.98 u
- Oxygen (O): 16.00 u

Calculating the formula mass:
Formula mass = (Number of aluminum atoms x Atomic mass of aluminum) + (Number of oxygen atoms x Atomic mass of oxygen)

Plugging in the values:
Formula mass = (2 x 26.98) + (3 x 16.00)
Formula mass = 53.96 + 48.00
Formula mass = 101.96 u (rounded to two decimal places)

Therefore, the formula mass of aluminum peroxide (Al2(O2)3) is approximately 102.0 u.

(c) Water, H2O:
To calculate the formula mass of water, you need to determine the atomic mass of hydrogen (H) and oxygen (O). The molecular formula H2O indicates that there are 2 hydrogen atoms and 1 oxygen atom.

Atomic masses:
- Hydrogen (H): 1.01 u
- Oxygen (O): 16.00 u

Calculating the formula mass:
Formula mass = (Number of hydrogen atoms x Atomic mass of hydrogen) + (Number of oxygen atoms x Atomic mass of oxygen)

Plugging in the values:
Formula mass = (2 x 1.01) + (1 x 16.00)
Formula mass = 2.02 + 16.00
Formula mass = 18.02 u (rounded to two decimal places)

Therefore, the formula mass of water (H2O) is approximately 18.0 u.