Chemistry Question

Question

What would the combined mass (in grams) be of the following samples? 0.48 mol barium phosphate, 58.7 L of bromine gas (at STP) and 3.58x10^21 molecules of SCl2

Answer 1

First of all, all elements have a molar mass. The molar mass of the element is roughly equal to their atomic number, but they're denoted by the number (with decimals) at the bottom of an element on the periodic table. The molar mass is the weight, in grams, of a mol of a pure substance.

So, let's take apart what we're given.

Barium Phosphate is Ba₃(PO₄)₂. We know this because Barium is a Group 2 element, and gives 2 electrons. Phosphate (PO₄) is an anion that takes 3 electrons. Since we must take/give the same number of electrons, we have 3 Barium and 2 Phosphates. We can find the atomic masses for each of the elements present in this.

Barium (Ba): 137.33 g/mol

Phosphorous (P): 30.974 g/mol

Oxygen (O): 15.999 g/mol

Ba₃(PO₄)₂ atomic mass = (137.33 g/mol) x 3 + ((30.974 g/mol) x 1 + (15.999 g/mol) x 4) x 2

Ba₃(PO₄)₂ atomic mass = 601.93 g/mol

So the mass of just Barium Phosphate is:

.48 mol x 601.93 g/mol.

For SCl₂, we will need to convert molecules to moles. This is done with Avogadro's Number.

6.022 x 10²³ molecules = 1 mol.

Apply this and solve as we did with Barium Phosphate, by finding the masses of S and Cl, adding them up to find the grams/mol, and converting the number of molecules into the number of mol...

For bromine gas, we should first recognize that bromine is a diatomic element. Meaning, Br₂ is the gas. STP, or standard temperature and pressure, is defined as 0 celsius (or 273.15 Kelvin), and 1 atm pressure. We can use the ideal gas law to find the number of mols.

PV = nRT

Where P is the pressure (in atmospheres), V is the volume (in liters), n is the number of mols, T is the temperature (in Kelvine), and R is one of the different constants that represent R. This will typically be given to you in an exam. For now, let's use this version of the constant

R = 0.08205 L atm / mol. K

Solve for n in the PV = nRT equation and you have the mols of bromine gas (Br₂)

Add all three values together to get the combined mass (in grams).

Answer 2

Barium phosphate = Ba3(PO4)2 . Molar mass = 602 g/mole

0.48 moles x 602 g/mole = 288.96 g = 290 g

Bromine gas = Br2. Molar mass = 160 g/mole

58.7 L x 1 mole/22.4 L x 160 g/mole = 419 g

SCl2 = sulfur dichloride. Molar mass = 103 g/mol

3.58x10²¹ molecules SCl₂ x 1 mole/6.02x10²³ molecules x 103 g/mole = 0.613 g

Adding all the masses, we get 710 g