What is the concentration (in M) of a carbonic acid (H2CO3) if 45.2 g of acid are dissolved in enough water to make 250.0 mL of solution?

Expert Answers
jerichorayel eNotes educator| Certified Educator

Molarity is defined as the moles of solute per liter of the solution. It is expressed as:

`Molarity = (mol es solute)/(L of solution)`

Moles of solute: 45.2 g/62.03 g/mol = 0.7287 moles carbonic acid (H2CO3)

Volume of solution: 250mL/1000mL = 0.250L

*Molar mass H2CO3 = 62.03 g/mol

`Molarity = (0.7287 mol es)/(0.250 L)`

`Molarity =2.9147 (mol es)/(L) =2.91 M`

To prepare the carbonic acid solution, weigh 45.2 grams of H2CO3 then add water until it reaches the 250 mL mark. 

nav1996 | Student

In order to determine concentration, we must use the formula for molarity, which is defined as follows:

Molarity = moles of solute/liters of solution

Since we are given the amount of solute in grams, we must convert it to moles. In order to determine the molar mass of H2CO3, we can add up the molar masses of the individual elements that make up H2CO3. 

1.008 (Hydrogen) x 2 +

12.01 (Carbon) x 1 +

16.00 (Oxygen) x 3

= 62.026 g/mol

Now, to convert from grams to moles,

45.2 g/62.026g/mol = 0.729 mol

To convert 250 mL into liters:

250mL/1000mL/L = 0.250 L

Now we can substitute these values in for our original equation:

Molarity = moles of solute/liters of solution

Molarity = 0.729 moles/0.250L = 2.91 mol/L or 2.91 M

ayl0124 | Student

The equation for molarity is:

`"M" = "mol"/"L"`

Since you know grams, you have to convert it into moles using dimensional analysis. Likewise, you must convert mL into L.

`45.2"g" = (1"mol")/(62.026"g") = 0.729 "mol"`

`250"mL" = (1"L")/(1000"mL") = 0.250"L"`

Plug in your known values.

`"M" = (0.729"mol")/(0.250"L")`

`"M" = 2.91` 

The answer will be in three sig figs: 2.91M.