Question

Calculate the concentration (in molarity) of an NaOH solution if 25.0mL of the solution is needed to neutralize 17.9 mL of a 0.323 M HCl solution.

Answer 1

Ok, so we need to calculate the concentration, right? What is the formula?

Answer 2

C = (# moles)/(vol of solution in liters)

Answer 3

That's right. And we are given...?

Answer 4

volume solution =25.0

Answer 5

Perfect. That leaves us moles to find

Answer 6

Yes

Answer 7

How would you find it with these information? "the solution is needed to neutralize 17.9 mL of a 0.323 M HCl solution."

Answer 8

Getting moles from the molar mass of NaOH

Answer 9

No that wouldn't be right

Answer 10

You are given C and V of HCl. What can you get from these info?

Answer 11

Would you multiple the (17.9)(.323)

Answer 12

Right. That's moles of HCl, right?

Answer 13

yes

Answer 14

=5.7817 is what I got

Answer 15

Yes, and the unit is mmol since you haven't convert mL to L. But you don't have to

Answer 16

Ok. Now, how that's gonna help us find the moles of NaOH that we need?

Answer 17

M = (5.7817)/(.025) =

Answer 18

Because H = OH

Answer 19

That's right.

Answer 20

However, since it is 5.7817 mmol, the volume should be in mL

Answer 21

Because you haven't converted 17.9 mL to L

Answer 22

Right

Answer 23

.231268

Answer 24

I have a feeling that you have a clear idea about this now

Answer 25

It's much better than before. That's for sure

Answer 26

I get tripped up on the problems if they are worried differently

Answer 27

See, it is like you are reading a question and you search an article to find the answer

Answer 28

You look for what you need to help answer it

Answer 29

Since you know what you need to find, different info won't affect much

Answer 30

Do you have any more problems?

Answer 31

I want to see how you plan to solve it

Answer 32

I do

Answer 33

Great. Practicing will help you get used to it

Answer 34

Btw, well done

Answer 35

Thank you. You are good at explaining

Answer 36

Thank you

Answer 37

You're welcome

Answer 38

What volume of a 5.00 M HCl solution is needed to neutralize each of the following:

(a) 20.0 mL of a 0.300 M NaOH solution

(b) 17.0 mL of a 0.200 M Ba(OH)2 solution

Answer 39

Ok. What is your thought? What should we do first?

Answer 40

Try to find the volume since that is what it is asking for

Answer 41

That's right. Then how do you do it?

Answer 42

Is this one going to be like the one we just did?

Answer 43

Exactly the same. Both acid and base are monoprotic

Answer 44

However, for (b), you should pay attention to the OH- group. \(1Ba(OH)_2\longrightarrow 2OH^-\)

Answer 45

So we need to find moles?

Answer 46

Yes

Answer 47

So you would find moles of the NaOH

Answer 48

That's correct. Then from there, you can calculate V of HCl

Answer 49

So you would use the .300 to get the moles right?

Answer 50

Yes

Answer 51

.300/39.988= .0075022507 moles

Answer 52

No. Moles of NaOH = concentration x volume

Answer 53

11.9964

Answer 54

You can't divide the concentration by MM of NaOH to find moles, right?

Answer 55

Yeah

Answer 56

Wait, are you on (a) or (b)? Because they are different problems

Answer 57

a

Answer 58

Alright. How did you calculate moles of NaOH?

Answer 59

.300 * 39.988 = 11.9964

Answer 60

Wait. Moles of NaOH = concentration x volume = .300M x .0200L, right? We are not supposed to use MM

Answer 61

Oh

Answer 62

I got .006

Answer 63

That's right. Now you can calculate C of HCl

Answer 64

Find moles and use the .0200 L

Answer 65

.500 * .0200 = .01

Answer 66

Moles of NaOH = concentration x volume => Concentration = Moles of NaOH / volume

Answer 67

15

Answer 68

(.300)/(.0200)

Answer 69

No, you already got the moles here "I got .006". So it should be .006moles/5.000M

Answer 70

Oh

Answer 71

1.2

Answer 72

That's right

Answer 73

Are you tired?

Answer 74

Somewhat. It's been a long day but I wanna finish the homework tonight

Answer 75

Ok. Then let's move on to (b)

Answer 76

The 1.2 is the answer to a right?

Answer 77

That's right. 1.2mL. Oops, I thought we are calculating the concentration. So I have been confusing you. I am so sorry

Answer 78

It's okay. You didn't mean to

Answer 79

We're probably both tired

Answer 80

Ok I will do my best on (b)

Answer 81

First let's calculate \(n_{OH-}\)

Answer 82

Are you awake?

Answer 83

.0034

Answer 84

Yeah. Just took me a bit to get it

Answer 85

Lol. Just to make sure

Answer 86

That's moles of Ba(OH)2?

Answer 87

Yes

Answer 88

Ok. What is the moles of HCl reacted with that amount of Ba(OH)2?

Answer 89

.0017

Answer 90

Wait you divide so .0068

Answer 91

That's right this time

Answer 92

The .0017?

Answer 93

Good job. Don't make mistakes on the easy ones :)

Answer 94

No. .0068 is correct

Answer 95

Good

Answer 96

Now could you tell me the volume of HCl needed?

Answer 97

Would you take (.500)(.0068)

Answer 98

No. V = moles / C = .0068 / 5.000