Question

Give the number of atoms of the specified element in a formula unit of each of the following compounds, and calculate the molecular (formula) mass: (a) Oxygen in aluminum sulfate. A12(SO4)3 (b) Hydrogen in ammonium hydrogen phosphate, (NH4)2HPO4 (c) Oxygen in the mineral azurite, Cu3(OH)2(CO3)2

Answer 1

The number of oxygen atoms in aluminum sulfate is 12 and the molecular (formula) mass of aluminum sulfate is 342.30 amu. The number of hydrogen atoms in ammonium hydrogen phosphate is 9 and the formula mass is 132.14 amu. The number of oxygen atoms in azurite is 8 and the formula mass is 398.72 amu.

Step-by-step explanation:

(a) To find the number of oxygen atoms in aluminum sulfate, A12(SO4)3, we can count the number of oxygen atoms in the compound. Since there are three sulfate ions, which contain 4 oxygen atoms each, the total number of oxygen atoms is 4 x 3 = 12.

The formula mass of aluminum sulfate can be calculated by adding up the atomic masses of each element in the compound. The atomic mass of aluminum is 26.98 amu, sulfur is 32.07 amu, and oxygen is 16.00 amu. So, the formula mass of aluminum sulfate is (2 x 26.98) + (3 x 32.07) + (12 x 16.00) = 342.30 amu.

(b) To find the number of hydrogen atoms in ammonium hydrogen phosphate, (NH4)2HPO4, we can count the number of hydrogen atoms in the compound. There are two ammonium ions, which each contain 4 hydrogen atoms, and one hydrogen phosphate ion, which contains 1 hydrogen atom. So, the total number of hydrogen atoms is 2 x 4 + 1 = 9.

The formula mass of ammonium hydrogen phosphate can be calculated by adding up the atomic masses of each element in the compound. The atomic mass of nitrogen is 14.01 amu, hydrogen is 1.01 amu, phosphorus is 31.00 amu, and oxygen is 16.00 amu. So, the formula mass of ammonium hydrogen phosphate is (2 x 14.01) + (9 x 1.01) + 31.00 + (4 x 16.00) = 132.14 amu.

(c) To find the number of oxygen atoms in azurite, Cu3(OH)2(CO3)2, we can count the number of oxygen atoms in the compound. There are two carbonate ions, which each contain 3 oxygen atoms, and two hydroxide ions, which each contain 1 oxygen atom. So, the total number of oxygen atoms is 2 x 3 + 2 x 1 = 8.

The formula mass of azurite can be calculated by adding up the atomic masses of each element in the compound. The atomic mass of copper is 63.55 amu, oxygen is 16.00 amu, hydrogen is 1.01 amu, and carbon is 12.01 amu. So, the formula mass of azurite is (3 x 63.55) + (8 x 16.00) + (2 x 1.01) + (2 x 12.01) = 398.72 amu.

Answer 2

For a: The number of oxygen atoms in given compound is
`7.2264* 10^(24)` and molecular mass of the compound is 342 g.

For b: The number of hydrogen atoms in given compound is
`5.4198* 10^(24)` and molecular mass of the compound is 132 g.

For c: The number of hydrogen atoms in given compound is
`4.8176* 10^(24)` and molecular mass of the compound is 344.5 g

Step-by-step explanation:

Formula units is defined as lowest whole number ratio of ions in an ionic compound. It is calculate by multiplying the number of moles by Avogadro's number which is
`6.022* 10^(23)`

Molecular mass is defined as the sum of atomic weights of all the atoms present in the molecular formula.

• For a:

We are given a chemical compound having formula of
`Al_2(SO_4)_3`

In 1 mole of aluminium sulfate, 2 moles of aluminium atoms, 3 moles of sulfur atoms and 12 moles of oxygen atoms are present.

So, number of atoms of oxygen in 1 formula unit of the compound =
`12* 6.022* 10^(23)=7.2264* 10^(24)`

Molecular mass of aluminium sulfate =
`[(27* 2)+3(32+(4* 16))]=342g`

Hence, the number of oxygen atoms in given compound is
`7.2264* 10^(24)` and molecular mass of the compound is 342 g.

• For b:

We are given a chemical compound having formula of
`(NH_4)_2HPO_4`

In 1 mole of ammonium hydrogen phosphate, 2 moles of nitrogen atoms, 9 moles of hydrogen atoms, 1 mole of phosphorus atom and 4 moles of oxygen atoms are present.

So, number of atoms of hydrogen in 1 formula unit of the compound =
`9* 6.022* 10^(23)=5.4198* 10^(24)`

Molecular mass of ammonium hydrogen phosphate =
`[2(14+(4* 1)+(1+31+(4* 16))]=132g`

Hence, the number of hydrogen atoms in given compound is
`5.4198* 10^(24)` and molecular mass of the compound is 132 g.

• For c:

We are given a chemical compound having formula of
`Cu_3(OH)_2(CO_3)_2`

In 1 mole of azurite, 3 moles of copper atoms, 2 moles of hydrogen atoms, 2 mole of carbon atom and 8 moles of oxygen atoms are present.

So, number of atoms of oxygen in 1 formula unit of the compound =
`8* 6.022* 10^(23)=4.8176* 10^(24)`

Molecular mass of azurite =
`[(3* 63.5)+2(16+1)+2(12+(3* 16))]=344.5g`

Hence, the number of hydrogen atoms in given compound is
`4.8176* 10^(24)` and molecular mass of the compound is 344.5 g