University:
Felician University
Course:
CHEM-001 | Basic Chemistry
Academic year:

2020
Views:

139

Pages:

10
Author:

MoonlitMarauder

UNIT CANCELLATION METHOD (AKA DIMENSIONAL ANALYSIS) WHEN TO USE IT: • WHEN PROPORTIONAL METHOD IS NOT USEFUL. • EXAMPLE: MAKE 100ML OF .35M CACL2 .35 mole CaCl2 x __1L_ x 1L 1,000 ml = 3.88 g CaCl2 110.98 g CaCl2 x 100ml 1 mole CaCl2 PRACTICE: • MAKE 5L OF A .22M NACL .22 mole NaCl 1L = 64.28g NaCl x 58.44 g NaCl x 5L 1 mole NaCl FOR TOMORROW: • MOLARITY PRACTICE PROBLEMS MAKING COMPOUND MOLAR SOLNS. What amount of salts are needed to make 100ml of a solution that contains .25M NaCl, and .05M CaCl2? .25mol NaCl x 1L ___ x 58.44 g NaCl 1L 1,000ml 1mol NaCl x 100ml = 1.46g NaCl .05 mol CaCl2 x 1L x 110.98 g CaCl2 x 100ml 1L 1,000ml 1mol CaCl2 = .55g CaCl2 To make 100ml solution of .25M NaCl and .05M CaCl2 calculate each mass separately. Then add each compound to a 100ml volumetric flask. Fill the flask ½ way with water, swirl to dissolve, then btv of 100ml per the meniscus reading. DILUTING MOLAR SOLUTIONS • STOCK SOLNS. THAT ARE STORED IN MOLAR CONCENTRATIONS MAY NEED TO BE DILUTED TO WORKING CONCS. M1 = Molarity of Stock Soln. M1V1 = M2V2 V1 = Volume of Stock Soln. M2 = Desired Molarity of final soln. V2 = Desired volume of solution EXAMPLE: Make 50ml of a .32 M NaCl from a .8M NaCl. M1V1 = M2V2 M1 = .8M M2 = .32M V2 = 50ml V1 = ?? .8M NaCl x V1 = .32M NaCl x 50ml V1 = 20ml of .8M NaCl PRACTICE PROB. Make 100µl of 50mM CaCl2 from a .5M CaCl2