# Question #a22ae

##### 1 Answer

#### Explanation:

Start by writing the balanced chemical equation that describes this *single replacement reaction*

#"Zn"_ ((s)) + color(red)(2)"HCl"_ ((aq)) -> "ZnCl"_ (2(aq)) + "H"_ (2(g)) uarr#

Notice that your reaction consumes **moles** of hydrochloric acid **for every mole** of zinc metal present in the coin.

Use the **molar mass** of zinc to determine how many moles you have in your sample

#3.0 color(red)(cancel(color(black)("g"))) * "1 mole Zn"/(65.38color(red)(cancel(color(black)("g")))) = "0.04589 moles Zn"#

Use the aforementioned mole ratio to find the number of moles of hydrochloric acid needed to ensure that **all the moles** of zinc metal get converted to zinc cations

#0.04589 color(red)(cancel(color(black)("moles Zn"))) * (color(red)(2)color(white)(a)"moles HCl")/(1color(red)(cancel(color(black)("mole Zn")))) = "0.09178 moles HCl"#

Now, focus on finding the number of moles of hydrochloric acid present in your *initial* solution. A **moles** of hydrochloric acid **per liter of solution**, i.e. per

This means that your initial solution contains

#40.0 color(red)(cancel(color(black)("mL solution"))) * "6.0 moles HCl"/(10^3color(red)(cancel(color(black)("mL solution")))) = "0.240 moles HCl"#

Your reaction will consume **moles** of hydrochloric acid, which means that the **resulting solution** will contain

#overbrace("0.240 moles HCl")^(color(blue)("what you start with")) - overbrace("0.09178 moles HCl")^(color(purple)("what is consumed")) = "0.1482 moles HCl"#

Now all you have to do is use the known volume of the solution to figure out its new molarity. Determine how many moles you'd get *per liter* of the resulting solution

#10^3 color(red)(cancel(color(black)("mL"))) * "0.1482 moles HCl"/(40.0color(red)(cancel(color(black)("mL")))) = "3.706 moles HCl"#

This means that **after** the reaction is complete, the molarity of the solution will be

#color(darkgreen)(ul(color(black)("3.7 mol L"^(-1) = "3.7 M")))#

The answer is rounded to two **sig figs**.