Phosphorus pentachloride, PCl5, reacts with water to form

phosphoric acid, H3PO4, and hydrochloric acid, HCl.
PCl5(s) + 4H2O(�) → H3PO4(aq) + 5HCl(aq)
(a) What mass of PCl5 is needed to react with an excess quantity of H2O
to produce 23.5 g of H3PO4?
(b) How many molecules of H2O are needed to react with 3.87 g
of PCl5?

a) 49.9 g

To solve the given questions, we need to use stoichiometry. Stoichiometry involves calculating the mass, moles, or molecules of substances involved in a chemical reaction.

(a) What mass of PCl5 is needed to react with an excess quantity of H2O to produce 23.5 g of H3PO4?

Step 1: Write and balance the chemical equation:
PCl5(s) + 4H2O(l) → H3PO4(aq) + 5HCl(aq)

Step 2: Determine the molar mass of H3PO4:
H3PO4 = 1(1.007) + 3(1.008) + 1(15.999) + 4(16.00) = 98.00 g/mol

Step 3: Calculate the moles of H3PO4:
moles of H3PO4 = mass of H3PO4 / molar mass of H3PO4
moles of H3PO4 = 23.5 g / 98.00 g/mol ≈ 0.239 moles

Step 4: Use the balanced equation to find the moles of PCl5:
From the balanced equation, we can see that 1 mole of PCl5 reacts with 1 mole of H3PO4. Therefore,
moles of PCl5 = moles of H3PO4 = 0.239 moles

Step 5: Calculate the mass of PCl5:
mass of PCl5 = moles of PCl5 x molar mass of PCl5
mass of PCl5 = 0.239 moles x (30.97 g/mol + 5(35.453 g/mol))
mass of PCl5 ≈ 0.239 moles x 208.41 g/mol ≈ 49.8 g

Therefore, approximately 49.8 g of PCl5 is needed to react with an excess quantity of H2O to produce 23.5 g of H3PO4.

(b) How many molecules of H2O are needed to react with 3.87 g of PCl5?

Step 1: Write and balance the chemical equation:
PCl5(s) + 4H2O(l) → H3PO4(aq) + 5HCl(aq)

Step 2: Determine the molar mass of PCl5:
PCl5 = 30.97 g/mol + 5(35.453 g/mol) = 208.41 g/mol

Step 3: Calculate the moles of PCl5:
moles of PCl5 = mass of PCl5 / molar mass of PCl5
moles of PCl5 = 3.87 g / 208.41 g/mol ≈ 0.0186 moles

Step 4: Use the balanced equation to find the moles of H2O:
From the balanced equation, we can see that 1 mole of PCl5 reacts with 4 moles of H2O. Therefore,
moles of H2O = moles of PCl5 x 4
moles of H2O = 0.0186 moles x 4 ≈ 0.074 moles

Step 5: Calculate the number of molecules of H2O:
molecules of H2O = moles of H2O x Avogadro's number
molecules of H2O = 0.074 moles x 6.022 x 10^23 molecules/mol
molecules of H2O ≈ 4.47 x 10^22 molecules

Therefore, approximately 4.47 x 10^22 molecules of H2O are needed to react with 3.87 g of PCl5.

To solve these problems, we will use stoichiometry, which is a method that relates the amount of substances involved in a chemical reaction. We start by writing a balanced chemical equation for the reaction:

PCl5(s) + 4H2O(ℓ) → H3PO4(aq) + 5HCl(aq)

(a) What mass of PCl5 is needed to react with an excess quantity of H2O to produce 23.5 g of H3PO4?

To find the mass of PCl5, we need to determine the molar mass ratio between PCl5 and H3PO4. Let's calculate the molar mass of H3PO4:

H3PO4: 1(1.01 g/mol) + 3(16.00 g/mol) + 1(4(1.01 g/mol)) = 98.01 g/mol

From the balanced chemical equation, we see that 1 mole of PCl5 produces 1 mole of H3PO4. Therefore, the molar mass ratio is 1:1.

Now, we can use the molar mass ratio to find the mass of PCl5:

Mass of PCl5 = (Mass of H3PO4) × (Molar mass ratio of PCl5 to H3PO4)
= 23.5 g × (1 mol PCl5 / 98.01 g H3PO4)
≈ 0.2399 mol PCl5

The molar mass of PCl5 is calculated as follows:

PCl5: 1(30.97 g/mol) + 5(35.45 g/mol) = 208.23 g/mol

Now, we can calculate the mass of PCl5:

Mass of PCl5 = 0.2399 mol × 208.23 g/mol
≈ 49.8 g

Therefore, approximately 49.8 grams of PCl5 is needed to react with an excess quantity of H2O to produce 23.5 g of H3PO4.

(b) How many molecules of H2O are needed to react with 3.87 g of PCl5?

To find the number of molecules of H2O, we need to determine the mole ratio between PCl5 and H2O.

Let's calculate the number of moles of PCl5:

Number of moles of PCl5 = Mass of PCl5 / Molar mass of PCl5
= 3.87 g / 208.23 g/mol
≈ 0.0186 mol PCl5

From the balanced chemical equation, we see that 1 mole of PCl5 reacts with 4 moles of H2O. Therefore, the mole ratio is 1:4.

Now, we can calculate the number of moles of H2O:

Number of moles of H2O = (Number of moles of PCl5) × (Mole ratio of H2O to PCl5)
= 0.0186 mol PCl5 × 4 moles H2O / 1 mole PCl5
= 0.0744 mol H2O

Finally, we can calculate the number of molecules of H2O using Avogadro's number:

Number of molecules of H2O = (Number of moles of H2O) × (6.022 × 10^23 molecules/mol)
≈ 0.0744 mol × (6.022 × 10^23 molecules/mol)
≈ 4.48 × 10^22 molecules

Therefore, approximately 4.48 × 10^22 molecules of H2O are needed to react with 3.87 g of PCl5.

PCl5(s) + 4H2O(�) → H3PO4(aq) + 5HCl(aq)

mols H2O = grams/molar mass = 23.5/18 = ?
Use the coefficients in the balanced equation to convert mols H2O to mols PCl5. Then convert mols PCl5 to g. g = mols x molar mass.

Part b.
Done the same way to find mols H2O then convert to # molecules remembering that 1 mol contains 6.02E23 molecules.