a monoacid base contains 53.3% carbon, 15.5% hydrogen and 31.2% nitrogen. 1.0g of the chloroplatinate of the base gave 0.39g of platinum. what is the molecular formula of the base?

To determine the molecular formula of the monoacid base from the given data, we need to follow a series of logical steps that involve calculating the molar mass of the base and then using the composition percentages to find the empirical formula. Let’s break this down step by step.

Step 1: Calculate the Moles of Platinum

First, we need to find out how many moles of platinum (Pt) are present in the chloroplatinate of the base. The molar mass of platinum is approximately 195.08 g/mol. Given that we have 0.39 g of platinum, we can calculate the moles of platinum as follows:

• Moles of Pt = mass of Pt / molar mass of Pt
• Moles of Pt = 0.39 g / 195.08 g/mol ≈ 0.00200 moles

Step 2: Determine the Moles of the Base

In a chloroplatinate complex, the number of moles of platinum corresponds to the number of moles of the base. Therefore, we have approximately 0.00200 moles of the base.

Step 3: Calculate the Molar Mass of the Base

Since we have 1.0 g of the chloroplatinate, we can find the molar mass of the base using the moles we just calculated:

• Molar mass of the base = mass of the base / moles of the base
• Molar mass of the base = 1.0 g / 0.00200 moles = 500 g/mol

Step 4: Determine the Empirical Formula

Now, we will use the percentage composition of the base to find the empirical formula. The base contains:

• 53.3% Carbon (C)
• 15.5% Hydrogen (H)
• 31.2% Nitrogen (N)

Assuming we have 100 g of the base, we can convert these percentages to grams:

• Carbon: 53.3 g
• Hydrogen: 15.5 g
• Nitrogen: 31.2 g

Step 5: Convert Grams to Moles

Next, we convert these masses to moles using their respective molar masses:

• Moles of C = 53.3 g / 12.01 g/mol ≈ 4.44 moles
• Moles of H = 15.5 g / 1.008 g/mol ≈ 15.36 moles
• Moles of N = 31.2 g / 14.01 g/mol ≈ 2.23 moles

Step 6: Find the Simplest Whole Number Ratio

To find the empirical formula, we need to divide each of the mole values by the smallest number of moles calculated:

• For Carbon: 4.44 / 2.23 ≈ 2
• For Hydrogen: 15.36 / 2.23 ≈ 7
• For Nitrogen: 2.23 / 2.23 = 1

This gives us a ratio of approximately C₂H₇N.

Step 7: Determine the Molecular Formula

Now, we need to find the molecular formula. The empirical formula mass of C₂H₇N is:

• Empirical formula mass = (2 × 12.01) + (7 × 1.008) + (1 × 14.01) ≈ 43.06 g/mol

Next, we divide the molar mass of the base by the empirical formula mass:

• 500 g/mol / 43.06 g/mol ≈ 11.6

Since we can only have whole numbers in a molecular formula, we round this to 12. Thus, we multiply the subscripts in the empirical formula by 12:

• C₂H₇N becomes C₂₄H₈₄N₁₂.

Therefore, the molecular formula of the monoacid base is C₂₄H₈₄N₁₂.