Calculate the percent by weight of a solution that contains 30.0g HCl in 400g of water?

To calculate the percent by weight of the solution, we need to first calculate the total weight of the solution.

Total weight of the solution = weight of HCl + weight of water
Total weight of the solution = 30.0g + 400g
Total weight of the solution = 430.0g

Now, we can calculate the percent by weight of HCl in the solution:

Percent by weight of HCl = (weight of HCl / total weight of the solution) x 100
Percent by weight of HCl = (30.0g / 430.0g) x 100
Percent by weight of HCl = 0.0698 x 100
Percent by weight of HCl = 6.98%

Therefore, the percent by weight of the solution that contains 30.0g HCl in 400g of water is 6.98%.

$$Percent \space by \space weight = \frac{Mass \space of \space solute}{Mass \space of \space solution} \times 100$$
$$Percent \space by \space weight = \frac{30.0g}{400g+30.0g} \times 100$$
$$Percent \space by \space weight = \frac{30.0g}{430.0g} \times 100$$
Percent by weight = 6.98%