Answer: 7.44 g of potassium bromide should be added to water to prepare the solution.
Step-by-step explanation:
The first thing we need to look for is the key parts of the question.
Since 0.125 M is a conversion factor we can rewrite it as 0.125 mol/L
When ever you see a question like this, always start with the "given" that's not a conversion factor, which is 0.50 L.
If we start with Liters, we need something to cancel it out to get all the way to grams. By using the conversion mol/L (from the 0.125 M) we can first get to moles.
0.5 L * 0.125 mol/L = 0.0625 mol
After getting to moles, we need to use a conversion factor to get to grams. By using the molar mass ratio (g/mol) we can figure this out. First we need to find the molar mass of Potassium Bromide, then put the units in a way where we can cancel it out. After multiplying the molar ratio (119.002 g/mol) by 0.0625 mol, we get 7.437625 g.
0.0625 mol * 119.002 g/mol = 7.437625 g
Last, we need to put the answer in the correct amount of significant figures.
Significant figures are the number of digits in a value that correlate with the accuracy of that value.
Based on the problem, the significant digits should be to the .01 place, due to 0.125 having the lowest digits of the problem (skip the first 0 because its on the left side of the decimal).
7.437625 g -> 7.44 g