3. Which of the following solutions below has a molarity of 1 M?
Answer: B
B: 53.6 g of NH4Cl in 1 L of water.
A solution containing 53.6 g of NH4Cl in 1 L of water has a molarity of 1 M, as calculated by dividing the number of moles of NH4Cl by the volume of the solution in liters. Given that the molar mass of NH4Cl is 53.6 g/mol, this concentration meets the definition of 1 M.
A) 58.4 g of NaCl in 100 L of water.
This option is incorrect because 58.4 g of NaCl in 100 L of water results in a very low molarity. The number of moles of NaCl is 1 (58.4 g / 58.4 g/mol), and when divided by 100 L, the molarity calculates to 0.01 M, which is significantly less than 1 M.
B) 53.6 g of NH4Cl in 1 L of water.
This option is correct. Since the molar mass of NH4Cl is 53.6 g/mol, dissolving 53.6 g in 1 L of water yields exactly 1 mole of NH4Cl, resulting in a molarity of 1 M (1 mole / 1 L = 1 M).
C) 100 g of CaCO3 in 10 L of water.
This option is incorrect as well. The molar mass of CaCO3 is 100 g/mol, so 100 g corresponds to 1 mole. However, when this mole is divided by 10 L, the molarity is only 0.1 M (1 mole / 10 L), which does not meet the criteria for 1 M.
D) 180 g of C6H12O6 in 0.1 L of water.
This option is also incorrect. The molar mass of C6H12O6 is 180 g/mol, meaning that 180 g corresponds to 1 mole. When this amount is dissolved in 0.1 L, the molarity is calculated as 10 M (1 mole / 0.1 L), which is much higher than 1 M.
Conclusion
Option B is definitively correct as it provides exactly 1 M concentration by using the correct mass of NH4Cl in the appropriate volume of solution. In contrast, all other options either yield a molarity that is too low or too high, failing to meet the requirement of a 1 M solution.