You need to prepare 500 mL of a 0.2 M sodium chloride (NaCl) solution. How many grams of NaCl do you need? (Molar mass of NaCl = 58.5 g/mol)

Question

BlackTom AI · Accepted Answer

First, translate the desired volume and concentration into moles: 500 mL is 0.5 L, and 0.2 M means 0.2 moles per liter.

So the required amount of NaCl in moles is 0.2 mol/L × 0.5 L = 0.1 mol.

Next, convert moles to grams using the molar mass of NaCl: 0.1 mol × 58.5 g/mol = 5.85 g.

Now evaluate the answer choices:
- 58.5 g: This would correspond to 1 mole of NaCl (since 1 mol × 58.5 g/mol = 58.5 g). It overestimates the amount needed by a factor of 10 in this problem, given we need 0.1 mol, not 1 mol.
- 11.7 g: This equals 0.2 mol × 58.5 g/mol? Not exactly: 0.2 mol × 58.5 g/mol would be 11.7 g, but that would require 0.2 moles, i.e., 1 L of 0.2 M solution, whereas we need only 0.5 L. This shows a mismatch in either moles or volume assumptions.
- 117 g: This would correspond to 2 moles of NaCl (2 mol × 58.5 g/mol = 117 g). It’s too high for the 0.1 mol required.
- 5.85 g: This matches 0.1 mol of NaCl (0.1 mol × 58.5 g/mol = 5.85 g), which aligns with the calculation for 0.5 L of a 0.2 M solution.

Therefore, the correct amount to weigh out is 5.85 g, and the other options reflect miscalculations related to incorrect moles or misapplied volume relationships.

You need to prepare 500 mL of a 0.2 M sodium chloride (NaCl) solution. How many grams of NaCl do you need? (Molar mass of NaCl = 58.5 g/mol)单项选择题

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