Question

after the mixture is poured, the initial mass of the material on the filter paper and the initial mass of the solution in the flask are measured. all of the water is allowed to evaporate, and the final masses are measured. the data are given in the following table.
which of the following equations should be used to determine the percent of nacl(s), by mass, in the original sample?
(a) \\( \frac { 15 } { 40 } \times 100 \\)
(b) \\( \frac { 25 } { 40 } \times 100 \\)
(c) \\( \frac { 14 } { 30 } \times 100 \\)
(d) \\( \frac { 6 } { 30 } \times 100 \\)

Explanation:

Step1: Calculate the mass of NaCl

The mass of NaCl is the mass after water evaporates for \(Y\) (since \(Y\) represents the substance we assume to be \(NaCl\)). So the mass of \(NaCl\) is \(6g\).

Step2: Calculate the initial mass of the solution

The initial mass of the solution is the sum of the initial masses of \(X\) and \(Y\). So the initial mass is \(15 + 25=40g\).

Step3: Calculate the percentage of NaCl by mass

The formula for percentage by mass is \(\frac{\text{Mass of solute}}{\text{Mass of solution}}\times100\). Substituting the values, we get \(\frac{6}{40}\times 100\).

Answer:

D. \(\frac{6}{40}\times 100\)