Molarity

Submittted by:

Melvin D. Alas-as

Gem Krisna Pastrana

Byron Dipasupil

Jeremias Laqui

Jericho Rosales

Submitted to:

Mrs. Elizabeth Oabel

MOLARITY AND MOLALITYMolarity and molality are both measures of concentration of solutions. One is the ratio of moles to volume of the solution and the other is the ratio of moles to the mass of the solution.

Molarity(M)Molarity, also known as molar concentration, is the number of moles of a substance per liter of solution. Solutions labeled with the molar concentration are denoted with a capital M. A 1.0 M solution contains 1 mole of solute per liter of solution.In a more general term, Molarity is the ratio of the amount of moles of solute per liter of solution.

The formula is: Molarity(M) = Moles of solute / Volume of solution in Liters

From that equation, we can simply deduce that the unit of molarity is mole/L or simply M.

Sample Problems:

Calculate the molarity of a 40 gram sodium hydroxide in 200 cubic centimeters of solution.

Convert the volume of the solution in terms of liters.

200cc x (1mL/1cc) x (1L/1000mL) = 0.2L

Moles = mass in grams / molar mass

Molar mass of NaOH is equal to:

1(number of atoms of Na) x 23(Atomic weight of Na) = 23

1(number of atoms of O) x 16(Atomic weight of O) = 16

1(number of atoms of H) x 16(Atomic weight of H) = 1

23+16+1 = 40g/mole

Moles of solute = 40g / 40g/mole

Moles of solute = 1 mole

Substituting to the general equation,

M = Moles of solute / Volume of solution in Liters

M = 1mole/0.2L

M = 5mole/L or 5M

2. How many mL of solution will result when 49 g of H2SO4 is dissolved to make a 0.200 M solution?

First thing to do is to find the Molar Mass of the Sulfuric acid.

Molar mass of H2SO4 is equal to:

2(number of atoms of H) x 1(Atomic weight of H) = 2

1(number of atoms of S) x 16(Atomic weight of S) = 32

4(number of atoms of O) x 16(Atomic weight of O) = 64

2+32+64 = 98g/mole


Moles of solute = 0.5 moles

Substituting to the general equation;

M = Moles of solute / Volume of solution in Liters

0.2 M = 0.5 mole / Volume of solution in Liters

Volume of solution in Liters= 0.5 mole / 0.2 mole/L

Volume of solution in Liters=2.5L

Since the question asks for mL. Convert 2.5L to mL

2.5L x (1000mL/1L) = 2500mLMolality(m)

Molality is the number of moles of solute per kilogram of solvent. It is important the mass of solvent is used and not the mass of the solution. Solutions labeled with molal concentration are denoted with a lower case m. A 1.0 m solution contains 1 mole of solute per kilogram of solvent.

In a more general term, Molality is the ratio of the amount of moles of solute per kg of solvent.

The formula is: Molality(m) = Moles of solute / Mass of solvent in Kg

From that equation, we can simply deduce that the unit of molarity is mole/Kg or simply molal.

Sample Problems:

Calculate the molality of a solution that contains 116grams of sodium chloride in 500g solvent.

Convert the mass of the solvent in terms of kilograms.

500g x (1 Kg/1000 g ) = 0.5Kg


Molar mass of NaCl is equal to:

1(number of atoms of Na) x 23(Atomic weight of Na) = 23

1(number of atoms of Cl) x 35(Atomic weight of O) = 35

23+35 = 58g/mole


Moles of solute = 2 moles


m = Moles of solute / Mass of Solvent in Kg

m = 2mole/0.5Kg

m= 4mole/Kg or 4M2. Calculate the molality when 282 grams of MgCl2 is dissolved in 500.0 g of solvent.

Convert the mass of the solvent in terms of kilograms.

500g x (1 Kg/1000 g ) = 0.5Kg


Molar mass of MgCl2 is equal to:

1(number of atoms of Mg) x 24(Atomic weight of Na) = 24

2(number of atoms of Cl) x 35(Atomic weight of O) = 70

24+70 = 94g/mole


Moles of solute = 3 moles


m = Moles of solute / Mass of Solvent in Kg

m = 3mole/0.5Kg

m= 6 mole/Kg or 6 molalEXERCISES:

1. 80.0 grams of glucose (C6H12O6) is dissolved in enough water to make 1.00 L of solution. What is its molarity? [0.444M] How many grams of KMnO4 are needed to make 500.0 mL of a 0.200 M solution? [15.8g] 80.0 grams of glucose (C6H12O6) is dissolved in1.00 kg of water. Calculate the molality. [0.444molal]Calculate the molarity of 25.0 grams of KBr dissolved in 750.0 mL, [0.28M]5. When 2.00 grams of KMnO4 is dissolved into 100.0 mL of solution, what molarity results?[0.13M]QUIZ

1. 10.0 g of acetic acid (CH3COOH) is dissolved in 500.0 mL of solution. What molarity results?[0.33M]2. 49.8 grams of KI is dissolved in 1.00 kg of solvent. What is the molality?[0.3molal]3. 100.0 grams of sucrose (C12H22O11) is dissolved in 1.50 L of water. What is the molality?[0.195molal]

The molarity of a certain solution having a 0.5dm3 volume is measured and found to be 2mole/L. If its molality is 3molal, Find the mass of the solvent in grams. [333.33grams]

5. When 2.00 grams of KMnO4 is dissolved into 100.0 mL of solution, what molarity results?[0.13M]

Molarity

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