Question

Citric acid, H3C6H5O7, occurs in plants. Lemons contain 5% to 8% citric acid by mass. The acid is added to beverages and candy. An aqueous solution is 0.688 m citric acid. The density is 1.049 g/mL. What is the molar concentration?.

Answer 1

`M=0.637`

Step-by-step explanation:

For this question, we have to assume that we have 1 L of solvent. With the molality equation we can calculate the moles of solute, so:

`moles~=~m*L=~0.688*1=0.688~moles`

Then we can calculate the grams of solute using the molar mass :

molar mass of
`H_3C_6H_5O_7`=192.12 g/mol

`0.688~mol(192.12~g)/(1~mol)=132.17~g`

The density for water is 1 Kg/L, therefore 1 L of water equal to 1 Kg, the total mass of the solution would be:

1000 g + 132.17 g = 1132.17 g

With this value we can calculate the volume of the solution using the density, so:

`1132.17~g(1~mL)/(1.049~g)(1~L)/(1000~mL)=1.079~L`

Finally, we can calculate the molarity diving the moles by the volume, so:

`M=(0.688)/(1.079)=0.637`

Answer 2

5.46 M

Step-by-step explanation:

First, we need to know the molar mass of the citric acid, the molar masses of the elements are:

H = 1 g/mol

C = 12 g/mol

O = 16 g/mol

So the molar mass of the acid is: 8x1 + 6x12 + 7x16 = 192 g/mol

The mass of the acid is the number of moles multiplied by the molar mass, so:

m = 0.688x192 = 132.096 g

Then, the volume is the mass divided by the concentration:

V = 132.096/1.049 = 125.926 mL = 0.1259 L

So, the molar concentration is the number of moles divided by the volume in liters:

M = 0.688/0.1259

M = 5.46 M