Please help me ???

Question

During a summer research internship, Cabrial is asked to do lab work and prepare solutions for experiments to be run on samples that will come in from the field. He needs to prepare a 0.500 M NaOH solution but only have 12.0 M NaOH on the shelf. Show all calculations for the following questions. 

a) What is the molarity (M)? Define it. 

b) How many moles of NaOH are in 10.0 mL of 12.0 M NaOH solution?

b) What volume of water must be added to 10.0 mL of 12.0 M NaOH to make a solution that is 0.500 M NaOH? (Assume that the volumes are additive.)

Answer 1

Hello, Anjela,

a) What is the molarity (M)? Define it. 

Molarity is defined as moles/liter

b) How many moles of NaOH are in 10.0 mL of 12.0 M NaOH solution?

Trust the units to tell us how to answer this. 12.0M can also be written as 12.0 moles/liter. 10.0ml can be written as 0,01 liter. Now we can see that if we multiply these two numbers, liters will cancel, leaving just moles:

(0.10L)*(12.0 moles/L) = 1.2 moles

c) What volume of water must be added to 10.0 mL of 12.0 M NaOH to make a solution that is 0.500 M NaOH? (Assume that the volumes are additive.)

There are two ways this can be answered:

1. Calculate the moles in 10.0ml of 12.0M NaOH and then find the liters necessary to make a 0.50M NaOH solution.
2. (0.010L)*(12.0moles/L) = 0.12 moles NaOH
3. (0.12 moles/X ) = 0.50 moles/L , X = 0.24L : This means we need to add 230ml to the 10ml to make a total volume of 240ml (0.24L).
4. The second approach is to use the relationship M1V1 = M2V2. If M1 is 12.0M, V1 is 10ml, and M2 is 0.5M, we can say (12.0M)*(10ml) = 0.5M*X X = 240ml. Add 230ml to the 10ml starting solution.

Bob

Answer 2

Use this video as a guide to answer this question.

https://youtu.be/n7mWr-FLA6Y