Question

what is the ppt of a 500ml sample of water with 29 grams of dissolved salts? 29 ppt 30 ppt 38 ppt 48 ppt

Explanation:

Step1: Recall ppt formula

ppt (parts - per - thousand) is calculated as $\frac{\text{mass of solute}}{\text{mass of solution}}\times1000$. First, assume the density of water is $1\ g/mL$, so the mass of 500 mL of water is $m =
ho V=1\ g/mL\times500\ mL = 500\ g$. The mass of the solution is the sum of the mass of water and the mass of dissolved salts. So, $m_{solution}=500\ g + 29\ g=529\ g$.

Step2: Calculate ppt

Using the ppt formula $ppt=\frac{\text{mass of solute}}{\text{mass of solution}}\times1000=\frac{29\ g}{529\ g}\times1000\approx 54.82$. But if we assume the volume - based approximation (neglecting the small volume change due to salt dissolution and considering the mass of water as the mass of the solution for simplicity, which is a common approximation in some cases), $ppt=\frac{29\ g}{500\ g}\times1000 = 58\ ppt$. However, if we go by the more accurate method of considering the mass of the solution as the sum of solute and solvent mass:
\[ppt=\frac{29}{500 + 29}\times1000=\frac{29000}{529}\approx54.82\]
If we assume the mass of the solution is approximately the mass of water (a rough approximation), $ppt=\frac{29}{500}\times1000 = 58\ ppt$. Since the closest value to our calculations among the given options (assuming some level of approximation) is 58 ppt is not there and if we consider the less - accurate volume - based approximation conceptually used in some basic cases, we note that $\frac{29}{500}\times1000 = 58$ and the closest option to values around this is:

Answer:

38 ppt (Note: This is an approximation - based selection as the calculated value is around 54.82 - 58 depending on the approximation method, and 38 ppt is the closest among the given options in a multiple - choice context where exact values may not always be provided)