Question

A sample of seawater contains 0.000245 g of sodium chloride per mL of solution. How much sodium chloride is contained in 50.0 mL of this solution?

Answer 1

`0.01225g`

Explanation:

Using Dimensional Analysis we can set up the correct equation to find the desired result. If we want mass (grams) from a concentration and volume it is this:
`(g/(mL)) xx mL) = g`

`0.000245g xx 50.0 = 0.01225g`

Answer 2

`"50 mL"` of the given `"NaCl"` solution contains `"0.0123 g"` of `"NaCl"`.

Explanation:

This is basically a density problem, where the density is known:

`"0.000245 g/mL NaCl"` solution.

In this question, the mass of `"NaCl"` in `"50 mL"` of solution is unknown.

`"density"="mass"/"volume"`

To find mass when density and volume are known, we can rearrange the density formula to isolate mass.

`"mass"="density"xx"volume"`

Plug in the known values and solve for mass.

`50.0color(red)cancel(color(black)("mL NaCl sol'n"))xx(0.000245"g NaCl")/(1color(red)cancel(color(black)("mL NaCl sol'n")))="0.0123 g NaCl"=1.23xx10^(-2) "g NaCl"` (rounded to three significant figures)