The structure of potassium hydrogen phthalate (KHP) is given below. Write its molecular formula and calculate its molar mass (C12, H1, O16, K39) (Show calculations) (2 Points) OH O K
The Correct Answer and Explanation is:
Correct Answer:
Molecular formula of KHP (Potassium Hydrogen Phthalate):
C₈H₅KO₄
Molar mass calculation (using atomic masses: C = 12, H = 1, O = 16, K = 39):
- Carbon (C): 8 × 12 = 96
- Hydrogen (H): 5 × 1 = 5
- Potassium (K): 1 × 39 = 39
- Oxygen (O): 4 × 16 = 64
Total molar mass = 96 + 5 + 39 + 64 = 204 g/mol
Explanation
Potassium hydrogen phthalate, commonly known as KHP, is an important compound used in analytical chemistry, especially in acid-base titrations as a primary standard. Its structure consists of a benzene ring with two carboxyl groups attached to adjacent carbon atoms. One of the carboxyl groups is a carboxylic acid (-COOH), and the other is a carboxylate salt (-COO⁻) bonded to a potassium ion (K⁺). This combination gives KHP both acidic and ionic properties.
To determine its molecular formula, we count the atoms directly from the structure. The aromatic ring contributes six carbon atoms. There are two more carbons from the carboxyl groups, totaling eight carbon atoms (C₈). The structure shows five hydrogen atoms (H₅): four are bonded to the aromatic ring, and one is part of the hydroxyl group in -COOH. One potassium ion (K⁺) is present, and four oxygen atoms (O₄) come from the carboxyl groups.
Once we have the molecular formula, we can calculate its molar mass by multiplying the number of each type of atom by its atomic mass and summing them. Carbon (12), hydrogen (1), oxygen (16), and potassium (39) contribute to the final molar mass. The detailed calculation shows that the molar mass of KHP is 204 grams per mole.
This compound’s precise molar mass and stability make it highly reliable for standardizing solutions. In labs, it is often used to determine the concentration of basic solutions such as sodium hydroxide because it reacts in a 1:1 molar ratio with strong bases.
