Question

Given that sodium chloride is 39.0% sodium by mass, how many grams of sodium chloride are needed to have 400.mg of na present?

Answer 1

There should be 1.03 grams of sodium chloride to have 400. mg of Na present. This problem is an application of the concept of mass percent or percentage by mass.

FURTHER EXPLANATION

Percentage by mass is the ratio of the mass of the element and the mass of the compound.

$\% \ element = \frac{mass \ of \ element}{mass \ of \ compound}$

In the problem, the given mass percent 39.0% can be interpreted as 39.0 grams of Na are in 100 g of sodium chloride. Using this ratio, the mass of the compound required to obtain 400. mg of Na can be solved using the dimensional analysis below and the conversion factor between milligrams (mg) to grams (g):

$mass \ of \ NaCl \ = \ 400. \ mg \ Na \ (\frac{1 \ g}{1000 \ mg}) (\frac{100. \ g \ NaCl}{39.0 g})$

Getting the ratio of the products of the numerator and the products of the the denominator:

$mass \ of \ NaCl \ = 1.02564 \ g$

Since the number of significant figures in the given quantities is 3, the final answer must also have 3 significant digits. Therefore, the mass of sodium chloride that has 400. mg of Na is 1.03 g.

LEARN MORE

• Concentration brainly.com/question/12936072
• Dimensional Analysis brainly.com/question/1557970

Keywords:  concentration, mass percent

Answer 2

The mass percentage of Na in NaCl is 39.0%
This means that if there's 100 mg of NaCl , 39 mg of the compound is Na.
For compound to contain 39 mg Na - 100 mg of NaCl should be present.
Therefore for the compound to contain 400 mg - 100/39 x 400 - 1025.6 mg 
The mass of NaCl present should be 1.026 g