Find the percent by mass of sodium chloride in a 1.35 M NaCl solution. The density of the solution is 1.05 g/mL.

Video transcript

hey everyone today we're being asked to find the mass percent of potassium bromide in a solution. Now the question stem gives us two concrete values were given that the concentration of potassium bromide and solution it's more clarity is 3.10 molar KBR Aquarius were also given that the density of the solution is 1.23 g per milliliter. We'll keep this value in mind because we'll need it in a little bit. Now the question is asking us to find the mass percent. What this essentially means is we need to find what is the mass of solute which in this case is KBR divided by the mass of solution of solution And we multiply this value times that is our mass percent. Keep in mind that the mass is calculated in grams in this case. So looking back at our question were given more clarity and recall that polarity is nothing more than moles of solute malls of salute of KBR divided by leaders of solution. That is our polarity definition using this. Since we're given value for the polarity we can assume or plug in That we have 3.10 moles of kbr of potassium bromide for every one liter of solution that we have one L of solution. So with that in mind we can go ahead and start solving for the mass of potassium bromide first Were given or we've assumed that we have 3.1 moles of KBR because it makes her it's given in the problem and it makes our calculations a lot easier. So 3.10 moles of KBR. And we can multiply this by potassium bromide. Smolder mass. Now the molar mass of potassium bromide is simple to calculate from the periodic table. potassium has a molar mass of 39 g from all and browning has a molar mass of 80 g from all. So adding this together, we have 119 g per mole of KBR. Our units will cancel out and we will be left with 368.9 grams of potassium bromide. So that is our massive salute. Now using that same values that we got from the modularity given in the question we can say that we have one leader solution and since we're given the density we can convert the leaders to gramps. However before that we first need to convert leaders two ml. I recall that for every millimeter There is 10 to the -3 leaders. One million. So therefore if you want to convert one leader, let's write that a little better one liter of solution. two mL. We can multiply by the inverse of that one millimeter by 10 to the negative three liters. Our units will cancel out And we'll be left with 1000 ml. So now that we have our volume in leaders. Or sorry milliliters we can go ahead and convert that again. two milk, 2g. Using the identity we can find our or mass. So 1000 ml Times 1.23 g per liter. So our middle leaders will cancel out. And we will be left with 1230 g of solution. Plugging this back into our mass% 368. grams of KBR, divide that By 1230g of solution Multiply that value by a 100. And we get that the mass percent of potassium bromide in solution is 30% 30%. I hope that helped you guys and I hope to see you in the next one.