Calculate the mass percent of water in NiCl2:6H2O. 8. Calculate the mass of water present in 4.50 g of Ba(OH)2 2H2O. 9. Name this compound, Ca(NO3)2:4H20
The Correct Answer and Explanation is:
Question 1: Mass percent of water in NiCl₂·6H₂O
First, calculate the molar mass of each component:
- Ni: 58.69 g/mol
- Cl₂: 2 × 35.45 = 70.90 g/mol
- H₂O: 6 × (2.02 + 16.00) = 6 × 18.02 = 108.12 g/mol
Total molar mass = 58.69 + 70.90 + 108.12 = 237.71 g/mol
Mass percent of water = (108.12 / 237.71) × 100% = 45.5%
Question 2: Mass of water in 4.50 g of Ba(OH)₂·2H₂O
Calculate the molar mass:
- Ba: 137.33 g/mol
- O₂H₂: 2 × (16.00 + 1.01) = 34.02 g/mol
- H₂O: 2 × 18.02 = 36.04 g/mol
Total molar mass = 137.33 + 34.02 + 36.04 = 207.39 g/mol
Mass percent of water = (36.04 / 207.39) × 100% = 17.38%
Mass of water in 4.50 g = 4.50 × 0.1738 = 0.782 g
Question 3: Name of Ca(NO₃)₂·4H₂O
This is calcium nitrate tetrahydrate.
Explanation
Hydrated compounds are salts that contain water molecules in their crystal structure. This water is known as “water of hydration.” The notation for these compounds often uses a dot to separate the salt from the water, such as in NiCl₂·6H₂O. This means six water molecules are associated with each formula unit of nickel(II) chloride.
To find the mass percent of water, we calculate the mass of the water portion and divide it by the total molar mass of the hydrate. For NiCl₂·6H₂O, water makes up 108.12 grams of its total 237.71 g/mol molar mass, giving a mass percent of 45.5%. This is useful in stoichiometry and chemical preparation where precise water content matters.
Next, to determine the mass of water in a sample, such as 4.50 g of Ba(OH)₂·2H₂O, we first compute the percent composition of water (17.38%). Multiplying this by the sample mass gives us 0.782 g of water in 4.50 g of the compound.
Finally, naming hydrated compounds follows standard IUPAC rules: the ionic compound is named first (e.g., calcium nitrate), followed by a prefix indicating the number of water molecules (e.g., “tetrahydrate” for four). Therefore, Ca(NO₃)₂·4H₂O is named calcium nitrate tetrahydrate.
Understanding hydrates is crucial in chemistry, especially in laboratory analysis and industrial applications where accurate water content affects both chemical behavior and product quality.
