1. Unit A: Chemistry Topic: Calculating Concentrations
Science 20
Unit A: Chemistry
Topic: Calculating Concentrations

2. Do Now

3. Today… Calculating Molar Concentrations
Reviewing PPM and % Volume before your quiz tomorrow

4. Molar Concentration (C)
This refers to the number of moles of solute present per liter of solution.
It is calculated by finding the number of moles of the solute and dividing it by the volume of solution. C = moles of solute (n)
volume of solution (V)
If the number of moles is not given to you but the mass of the solute is then we use the following formula to find the number of moles.
n = m/M where n = number of moles (mol)
m= mass of solute (g)
M= molar mass of solute (g/mol)

5. Molar Concentration (C)
E.g., #1
Suppose you added water to 4.00 moles of sugar to get 10.0 L of solution. Calculate the molar concentration of the solution.

6. Molar Concentration V = 10.0 L n = 4.00mol C = ?
C = n = mol = mol/L
V L

7. Molar Concentration (C)
E.g., # 2
A sample of water taken from a nearby lake is found to have mol of salt in a 100 mL solution. Determine the concentration of the salt in the lake.

8. Molar Concentration (C)
n = mol
V = 100 mL = L
C = ?
C = n = mol = mol/L
V L
C = 3.5 x 10-2 mol/L

9. Molar Concentration (C)
E.g., #3
You dissolve 30.0 g of sodium sulfate, Na2SO4(s), into 300 mL of water.

10. Molar Concentration m = 30.0 g V = 300 mL = 0.300L n = ? C = ?
We must first solve for the number of moles (n) by using n = m M

11. Molar Concentration m = 30.0 g M = ? Calculate the molar mass
M = 2(M of Na) + (M of S) + 4(M of O)
= 2(22.99g/mol) + (32.06g/mol) + 4 (16.00g/mol)
= g/mol
n = m = g = mol
M g/mol
Now you can calculate C

12. Molar Concentration (C)
n = mol
V = L
C = n = mol = mol/L
V L

13. To Work On…
Page 42 # 28, 29
Page 44 # 31 (Use table on page 42 to help)
# 33
Page 46 # 34, 35, 36
* You must show ALL of your work. Remember to watch for sig. digs.

14. ANSWERS pg. 42 # 28
Vsolute = 30 mL
Vsolution = 70 mL
(% V/V ) = ?
                                                             

15. ANSWERS pg. 42 # 29
(% V/V ) = 60%
Vsolution = 200 mL
Vsolute = ?

16. ANSWERS pg. 42 # 30
(% V/V ) = 25%
Vsolution = 250 mL
Vsolute = ?

17. ANSWERS pg. 44 # 31 msolute = 8.30 × 10–3 g msolution = 250 g
parts per million = ?
The concentration of the lead in the water is 33.2 ppm.

18. ANSWERS pg. 44 # 32 parts per million = 2.00 ppm msolution = 227 g
msolute = ?

19. ANSWERS pg. 44 # 33 parts per million = 50.0 ppm m solution = 250 g
m solute = ?

20.                                   
                      
ANSWERS pg. 46 # 34 a
The molar concentration of the sodium chloride solution is 2.18 mol/L.

21. ANSWERS pg. 46 # 34 b The molar concentration of the sodium hydroxide
                                 
                      
The molar concentration of the sodium hydroxide
solution is mol/L.

22. ANSWERS pg. 46 # 35 a
                                          
                                
There are mol in 30.0 g of NaCl(s).

23. ANSWERS pg. 46 # 35 b
                                 
The molar concentration of the salt solution is mol/L.
Note: The unrounded value for the number of moles from
the answer to question 35.a. was used here to get a more
accurate calculation of molar concentration.

24. ANSWERS pg. 46 # 36
m = 5.00 g
V = 300 mL
C = ? First, determine the number of moles of solute.
M = 1(M of Na) + (M of O) + (M of H)
= g/mol g/mol g/mol
= g/mol
n = ?

25. ANSWERS pg. 46 # 36 Next, determine the molar concentration.
n = mol
C = ?
The molar concentration of the NaOH solution is mol/L.