Help needed - chemistry

[monolog]

Hi. I'm doing a chemistry assignment in which I'm having difficulties. I am on a open university course (Environmental Sciences, first year) and never had chemistry in high-school (coming from the services area), therefore I need some assistance. Whatever help i get is welcomed.
This is it:
A solution of 100 cm³ of acetic acid (CH₃COOH) with a concentration of 0.2 mol / L was titrated with aqueous sodium hydroxide solution (NaOH) at a concentration of 0.1 mol / L.
a) Write the chemical reaction that translates the titration.
b) What is the pH of the solution after adding 30mL of NaOH
c) In a titration what is the meaning of the expression "point of equivalence"? For the given example, calculate the volume of titrant needed to reach this point as well as the pH value.
Data: K_a = 1,80 × 10^-5

Thanks in advance.

Edited January 2, 2019 by monolog
grammar

[studiot]

1 hour ago, monolog said:

Hi. I'm doing a chemistry assignment in which I'm having difficulties. I am on a open university course (Environmental Sciences, first year) and never had chemistry in high-school (coming from the services area), therefore I need some assistance. Whatever help i get is welcomed.
This is it:
A solution of 100 cm³ of acetic acid (CH₃COOH) with a concentration of 0.2 mol / L was titrated with aqueous sodium hydroxide solution (NaOH) at a concentration of 0.1 mol / L.
a) Write the chemical reaction that translates the titration.
b) What is the pH of the solution after adding 30mL of NaOH
c) In a titration what is the meaning of the expression "point of equivalence"? For the given example, calculate the volume of titrant needed to reach this point as well as the pH value.
Data: K_a = 1,80 × 10^-5

Thanks in advance.

Well since you obviously know the chemical formulae of the reactants, surely you can do part (a) ?

You need to tell us something of your thoughts, as well as the question.

[monolog]

Part a is done, yes. How do I find the pH of any solution? 

[studiot]

3 minutes ago, monolog said:

Part a is done, yes. How do I find the pH of any solution? 

So what is your equation?

 

and have you read this?

 

 

Edited January 2, 2019 by studiot

[monolog]

NaOH + CH₃COOH → CH₃COONa + H₂O

I have read it. I'm looking to be guided, maybe get a step by step explanation of what is going on and what to do so I can answer the questions. Got time for that? I would appreciate it.

Edited January 2, 2019 by monolog

[studiot]

2 hours ago, monolog said:

NaOH + CH₃COOH → CH₃COONa + H₂O

I have read it. I'm looking to be guided, maybe get a step by step explanation of what is going on and what to do so I can answer the questions. Got time for that? I would appreciate it.

OK,  I'm trying to find out what you know here about the subject in hand.

Next question.

You have shown a reaction going to completion.

Does sodium acetate precipitate out?

If not what does actually happen?

 

Do you know what  Data: K_a = 1,80 × 10^-5  means?

 

Attached is a zipped powerpoint of a first year UK university lecture on the subject that may help with the background.

 

 

Have you done any reaction kinetics?

Are you familiar with the following equations

pH = -log[H⁺]

pOH = -log[OH^-]

-log[H⁺]-log[OH^-] = -14

pH+pOH = 14 = pK

pX = -logX

 

Note some modern authors like to use [H₃O⁺] or even more complicated formulae for [H⁺].

But this does not add anything but more writing to a calculation.

 

Attached is a zipped powerpoint of a UK University first year lecture about the subject that may help.

pHarch.zip

Edited January 2, 2019 by studiot

[hypervalent_iodine]

Are you familiar with the Henderson Hasselbach equation at all?

[studiot]

8 hours ago, hypervalent_iodine said:

Are you familiar with the Henderson Hasselbach equation at all?

Describing the H-H equation and its use was the main point of the lecture I posted.

[hypervalent_iodine]

1 hour ago, studiot said:

Describing the H-H equation and its use was the main point of the lecture I posted.

I am unsure of your point. I did not download the file, and felt it more appropriate to ask the relevant questions here in the thread. You also asked about reaction kinetics, which is largely unrelated to the question. 

[monolog]

Replying to Studiot:

Hi. Thanks for your time.

You asked for the equation and I gave you a reaction going to completion, which I believe is the answer to (a). I don't know how to put that in a equation.

Does sodium acetate precipitate out? I don't know. All I have is the given info.

If not what does actually happen? An acid and a base mix, but i don't even know how to identify an acid and a base without looking up the compounds online, meaning I'm in trouble when the exam comes.

Do you know what  Data: K_a = 1,80 × 10^-5  means? It's the acidity constant, but I honestly don't know what to do with it.

Have you done any reaction kinetics? No.

Are you familiar with the following equations? No. [H₃O⁺] , [H⁺] and [OH^-] are exchanged somehow, but I don't know what exchanges with what nor why (electronegativity?).

In sum, I don't think I can learn this on my own in time to finish this assignment and get a good grade. Will be needing a private tutor. Biology, geology and statistics, I can learn those on my own. Chemistry, no way.

If you think you can explain the basic rules behind the [H⁺] [OH^-] transfers so I can try and make the calculations, great. If not, thanks anyway.

 

10 hours ago, hypervalent_iodine said:

Are you familiar with the Henderson Hasselbach equation at all?

Hi, and thanks for taking the time to help me.

No, I am not familiar with it. I'll look it up now.
I do have literature given by the university, but with all of the classes' assignments piling up I didn't have time to study it. Acid-base equilibrium, titration, energy reactions, entropy, and Gibbs energy are the subjects I have fallen behind on. In order to succeed in this assignment I need to go straight to the point (I'll go through the whole semester later in preparation for the exam).

What do I need to focus on in order to answer these questions? Can you give me a step by step guide?

Thanks in advance.

This is the equation, right?

How does this: NaOH + CH3COOH → CH3COONa + H2O, translate into values in the equation? What does [A^-] and [HA] stand for?
 

Edited January 3, 2019 by monolog

[studiot]

21 minutes ago, monolog said:

In sum, I don't think I can learn this on my own in time to finish this assignment and get a good grade. Will be needing a private tutor. Biology, geology and statistics, I can learn those on my own. Chemistry, no way.

Then we need to start from the beginning.

First about this question

22 minutes ago, monolog said:

Does sodium acetate precipitate out? I don't know. All I have is the given info.

Pretty well all sodium compounds are soluble to very soluble.

A precipitate will only form if (one of) the products of the reaction are insoluble.

You only learn this sort of information by experience.

So there is no reason not to look it up. Just ask Google if sodium acetate is soluble.

This will give you practice and some chemical background lnowledge and gain you familiarity with chemical terms etc.

Next about pH.

Chemistry is a mathematical subject so you need some facility in basic maths.

One of the equations I wrote was pX = - logX

X stands for anything we want to calculate with and its p value is given by the negative logarithm.

Don't worry what or why p value yet

So the p value of the hydrogen ion concentration is written pH and another of my equations show that pH = -log[H⁺]

The square brackets are used to show we mean the concentration in mols/litre

The big question is

Do you know what logarithms and antilogarithms are or should I explain them?

 

You can also take the p value of other things eg the hydroxyl ion concentration and tha acidity constant K_a

We are heading towards the equation you want which is

pH = pK_a + log [salt]/[acid]

So you see it is vital you understand the necessary maths.

Look here about pH

https://www.materialstoday.com/materials-chemistry/comment/caustic-wit-acid-tongues-mind-your-ps-and-qs/

 

[monolog]

This is the equation, right?
pH = pK_a + log₁₀ ([A^-]/[HA])
How does this: NaOH + CH3COOH → CH3COONa + H2O, translate into values in the equation? What does [A^-] and [HA] stand for?

Edited January 3, 2019 by monolog

[studiot]

1 hour ago, monolog said:

What does [A^-] and [HA] stand for?

 

1 hour ago, studiot said:

The square brackets are used to show we mean the concentration in mols/litre

 

Are you reading my text?

and did you bother with the lecture I appended?

It was aimed at non Chemistry first year students.

Edited January 3, 2019 by studiot

[hypervalent_iodine]

2 hours ago, monolog said:

No, I am not familiar with it. I'll look it up now.
I do have literature given by the university, but with all of the classes' assignments piling up I didn't have time to study it. Acid-base equilibrium, titration, energy reactions, entropy, and Gibbs energy are the subjects I have fallen behind on. In order to succeed in this assignment I need to go straight to the point (I'll go through the whole semester later in preparation for the exam).

What do I need to focus on in order to answer these questions? Can you give me a step by step guide?

Thanks in advance.

This is the equation, right?

How does this: NaOH + CH3COOH → CH3COONa + H2O, translate into values in the equation? What does [A^-] and [HA] stand for?
 

 

[HA] is shorthand used to represent an acid, and [A-] is its conjugate base form. Do you know how to write equilibrium expressions, and can you give one for the dissociation of acetic acid? Are you familiar with ICE tables or how to write out equilibrium expressions and how to use those plus the K_a/b values to calculate pH?

At the moment it sounds like you are missing a lot of fundamental knowledge, and certainly too much to explain over a forum such as this. I can’t really give a step by step guide in this case, since it appears that you need an entire module’s worth of information given to you. You are better off studying this from the resources you already have had provided to you, and coming here with specific queries if something isn’t making sense. I realise this isn’t what it want, but it’s the best I can offer short of simply doing the work for you (which we do not do here).

 

[monolog]

22 hours ago, studiot said:

and did you bother with the lecture I appended?

Hi. I think my posts are limited to 5 daily, that's why I didn't reply. Yes, I did read it. As hypervalent_iodine says, I'm lacking too much fundamental knowledge. De-synced communication won't really help me right now. Thanks for your time anyway. I do appreciate you putting in the effort.

22 hours ago, hypervalent_iodine said:

At the moment it sounds like you are missing a lot of fundamental knowledge, and certainly too much to explain over a forum such as this. I can’t really give a step by step guide in this case, since it appears that you need an entire module’s worth of information given to you. You are better off studying this from the resources you already have had provided to you, and coming here with specific queries if something isn’t making sense. I realise this isn’t what it want, but it’s the best I can offer short of simply doing the work for you (which we do not do here).

You are right. I think I need a private tutor to help me at this point. I did find, however, a very helpful video which I believe will help me answer (b) and (c). Here it is: 

I thing I can solve the problem now. It does address the exact same problem, doesn't it?
Anyway, thank you very much for your time. I will keep this forum in mind, and also your recommendations. Best regards.

[StringJunky]

3 minutes ago, monolog said:

Hi. I think my posts are limited to 5 daily, that's why I didn't reply. Yes, I did read it. As hypervalent_iodine says, I'm lacking too much fundamental knowledge. De-synced communication won't really help me right now. Thanks for your time anyway. I do appreciate you putting in the effort.

Only on your first day: it's to deter spammers.

[hypervalent_iodine]

33 minutes ago, monolog said:

Hi. I think my posts are limited to 5 daily, that's why I didn't reply. Yes, I did read it. As hypervalent_iodine says, I'm lacking too much fundamental knowledge. De-synced communication won't really help me right now. Thanks for your time anyway. I do appreciate you putting in the effort.

You are right. I think I need a private tutor to help me at this point. I did find, however, a very helpful video which I believe will help me answer (b) and (c). Here it is: 

I thing I can solve the problem now. It does address the exact same problem, doesn't it?
Anyway, thank you very much for your time. I will keep this forum in mind, and also your recommendations. Best regards.

I don’t have time to watch the whole video, but my guess from the title that it does answer most of it except perhaps b, which is where you need the HH equation. If you know how to use the HH equation, then you’ll know the two values you need to determine are [HA] and [A-]. Do you know which species those correspond to in your question? Do you know how to work them out with the information you are given?

[monolog]

29 minutes ago, hypervalent_iodine said:

I don’t have time to watch the whole video, but my guess from the title that it does answer most of it except perhaps b, which is where you need the HH equation. If you know how to use the HH equation, then you’ll know the two values you need to determine are [HA] and [A-]. Do you know which species those correspond to in your question? Do you know how to work them out with the information you are given?

He actually uses the HH equation to find the pH.
Honestly, I don't know which species those correspond to in my equation. Would you explain it to me?
Luckily the value for both is 0,769, so I end up with log1 in the HH equation. The pH is 4.74. I hope I got it right.

[hypervalent_iodine]

4 minutes ago, monolog said:

He actually uses the HH equation to find the pH.
Honestly, I don't know which species those correspond to in my equation. Would you explain it to me?
Luckily the value for both is 0,769, so I end up with log1 in the HH equation. The pH is 4.74. I hope I got it right.

 

Where do you get 0.769 from if you don’t know what the values correspond to? Do you know which species the Ka is in reference to? Remember that if we are using HH, we are talking about a weak acid or base. Can you identify a weak acid and/or base in your question? 

[monolog]

This is what I did:

"Adding 30ml of NaOH gives us a 130ml solution. therefore:"

[studiot]

10 minutes ago, hypervalent_iodine said:

 

 Do you know which species the Ka is in reference to? Remember that if we are using HH, we are talking about a weak acid or base. Can you identify a weak acid and/or base in your question?  

 

To start

Please confirm you know what weak and strong mean in this context (by telling us the difference)

[monolog]

1 minute ago, studiot said:

Please confirm you know what weak and strong mean in this context (by telling us the difference)

I wouldn't be here if I knew. Being confronted with my ignorance does not help. Explaining things to me, does.

[hypervalent_iodine]

19 minutes ago, monolog said:

This is what I did:

"Adding 30ml of NaOH gives us a 130ml solution. therefore:"

Close! You’re mucking up the calculation of concentrations though. In part b., you cannot simply add and subtract the concentration values in the way that you have, particularly since once you add the two volumes together the concentrations change. I would suggest first calculating how many moles you have in the 100 mL of acetic acid and 30 mL of NaOH and rethinking the question with those numbers instead. 

 

[studiot]

20 minutes ago, monolog said:

I wouldn't be here if I knew. Being confronted with my ignorance does not help. Explaining things to me, does.

Loose the false indignation, we will help and my question was intended to do just that.

And it has achieved its objective.

A weak acid or base is one which is only partially dissociated into ions in solution.

A strong acid or base is fully dissociated.

For an acid, this means that the hydrogen ion concentration (which provides the low pH) is not as much as it could be, but if some are removed more acid will dissociate.

That is the basis for the dissociation constant Ka (the clue is a stands for acid).

 

Now can you attempt Hypervalent Iodine's questions?

 

[hypervalent_iodine]

25 minutes ago, monolog said:

I wouldn't be here if I knew. Being confronted with my ignorance does not help. Explaining things to me, does.

 

You should watch some more of those Kahn academy videos. They are quite good, and will help you in your understanding. You will need to spend some more time getting a better understanding of where all these numbers are coming from and how to use the equations and graphs, otherwise you will struggle when it comes to more complex questions. Based on your previous post, you also need to work on the more basic concepts related to stoicheometry, calculating how much product is formed from reactions, limiting reagent questions, etc. Google will provide you a wealth of resources to learn and practice these concepts from.