CHEM 120 Exam 2 - Practice questions

MOLARITY

Determine moles and Liters.

What is the molarity of 150 g NaCl dissolved in 750 mL of water?

1. Convert mL to L
2. Find the molecular weight of each molecule and add them together
3. Plug in numbers using dimensional

analysis Equation:

M=moles

L

750 mL 1L 750 L = .75 L
1000 mL 1000
Na= 23 Cl= 35
=58 g/mol
150 g NaCl 1 mol = 150 mol = 2.59 mol
58 g 58
SOLUTION DILUTION (make more dilute)
Equation: C1 V1 = C2 V2
The concentration will be in Molar or %. DO NOT convert. Keep mL or L as it is.
How much of a 1 molar solution can you make from 2 liters of a 10 molar
solution? C1= 10 M
V1= 2L
C2= 1 M
V2=? = 20 L
Solving for V2 therefore need to get it by itself.
C1 (V1) = C2 (V2) = 10M (2L) / 1M = 20L = 20 L
C2 C2
1 1
OSMOLARITY
Metal and Non-Metal. What is the osmolarity of a 5 molar Ca1Cl2 Solution?
Equation: Osm= M (i) Multiply molar by the subscript. 5 (3) = 15 Osm/L
MASS/VOLUME mass will need to be in grams and volume in %. Divide mass by volume then multiply by
100. Example: What is the mass/volume % of 300 g NaCl mL dissolved in 2 L of water? First convert to
mL then solve.
2L (1000mL) ( the Liters cancel out) = 2,000 mL
1L