4. A 35.0 mL sample of 1.00 M KBr and a 60.0-mL sample of 0.600 M KBr are mixed. The solution is then heated to evaporate water until the total volume is 50.0 mL. What is the molarity of the KBr in the final solution?
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To find the molarity of KBr in the final solution, we need to first determine the moles of KBr in each initial solution and then calculate the total moles of KBr in the final solution.
Let's begin by calculating the moles of KBr in the 35.0 mL sample of 1.00 M KBr. We can use the formula:
moles = concentration (M) × volume (L)
First, we convert the volume of the 35.0 mL sample to liters:
35.0 mL = 35.0 mL × (1 L / 1000 mL) = 0.0350 L
Next, we use the moles formula to calculate the moles of KBr in the 35.0 mL sample:
moles of KBr (35.0 mL) = 1.00 M × 0.0350 L = 0.0350 moles
Now, let's calculate the moles of KBr in the 60.0 mL sample of 0.600 M KBr. Again, we convert the volume to liters:
60.0 mL = 60.0 mL × (1 L / 1000 mL) = 0.0600 L
Using the moles formula, we calculate the moles of KBr in the 60.0 mL sample:
moles of KBr (60.0 mL) = 0.600 M × 0.0600 L = 0.0360 moles
Now, to determine the total moles of KBr in the final solution, we add the moles from the two samples:
total moles of KBr = moles of KBr (35.0 mL) + moles of KBr (60.0 mL) = 0.0350 moles + 0.0360 moles = 0.0710 moles
Finally, we calculate the molarity of KBr in the final solution using the formula:
molarity = moles / volume (in liters)
The volume of the final solution is given as 50.0 mL, so we convert it to liters:
50.0 mL = 50.0 mL × (1 L / 1000 mL) = 0.0500 L
Plugging the values into the formula, we find:
molarity of KBr (final solution) = 0.0710 moles / 0.0500 L = 1.42 M
Therefore, the molarity of KBr in the final solution is 1.42 M.