Chemistry Practice Questions: pH Mixture and Gas Production

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Discussion Overview

The discussion revolves around practice questions related to pH calculations and gas production in chemistry, specifically focusing on the mixture of hydrochloric acid (HCl) and barium hydroxide (Ba(OH)2), as well as the combustion of carbon to produce carbon dioxide (CO2). The scope includes conceptual understanding and problem-solving methods relevant for high school chemistry.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant expresses difficulty in understanding the method for calculating pH and gas volumes, seeking help with specific questions.
  • Another participant suggests a resource from Khan Academy for understanding acid-base calculations and offers to assist if the original poster shares their work.
  • A later reply indicates that the participant believes the pH of the mixture is 12.6, reasoning that since Ba(OH)2 fully dissociates and has a greater concentration of hydroxide ions, the solution is basic.
  • One participant questions the outcome of mixing the acid and base, noting the reaction produces salt and water, and considers the stoichiometry of the reactants.
  • Another participant confirms the pH result and mentions having resolved the question about CO2 production.

Areas of Agreement / Disagreement

Participants generally agree on the pH being closer to 12.6, but there is no consensus on the exact methodology or formulas to arrive at that conclusion. The discussion remains unresolved regarding the specific calculations for the gas production question.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the complete dissociation of the acids and bases, as well as the lack of detailed mathematical steps in the responses provided.

Omm
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I am only a high school student so take some pity, I have an exam tomorrow and am trying to teach myself the method. But alas, not working >.<

Could someone please answer them for me with working? My teacher kind of rushed over this and I didnt really understand:

Q1) The pH of a mixture of 50ml or 0.4 M HCl and 50ml 0.4 Ba(OH)2 is closest to:

12.6
7.0
14.0
1.0

Q2) What volume of CO2 gas at 25*C and 101.3kPa is produced by the complete combustion of 4.0g of carbon in oxygen?

25.4L
12.7L
8.47L
4.24L

Please show working + formulas

Thanks a heap!
 
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Khan Academy has a really great series of videos about calculating weak/strong acid/bases. I recommend you check out that series of videos located here:
http://www.khanacademy.org/video/introduction-to-ph--poh--and-pkw?playlist=Chemistry

It's only about 30 minutes long and he does a great job explaining exactly how to solve these questions.

If you prefer, if you write out what you have worked the questions to so far, I will help you get to the desired result.
 
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Thanks a heap! I will take a look at the video/s and see if I can get it :)
 
Yer, still having trouble. Could you please work the answer so I can see the process for 1?

EDIT: Ok I don't think there is like a formula or equation to follow for it? So it is just knowing that they both fully disassociate but Ba(OH)2 occupies more therefore it is basic. A pH of 14 in unreasonable with the HCl in the solution so by elimination it is 12.6?
 
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Omm said:
I am only a high school student so take some pity, I have an exam tomorrow and am trying to teach myself the method. But alas, not working >.<

Could someone please answer them for me with working? My teacher kind of rushed over this and I didnt really understand:

Q1) The pH of a mixture of 50ml or 0.4 M HCl and 50ml 0.4 Ba(OH)2 is closest to:

12.6
7.0
14.0
1.0

What happens when these two are mixed? acid + base -> ?

Omm said:
Q2) What volume of CO2 gas at 25*C and 101.3kPa is produced by the complete combustion of 4.0g of carbon in oxygen?

25.4L
12.7L
8.47L
4.24L

Please show working + formulas

Thanks a heap!

How many moles of CO2 is formed by the combustion?
 
Answer to A is 12.6. Acid + Base --> Salt + Water however there is one H in HCL but two OH in Ba(OH)2 This will shift the pH to more basic.

I got it now as well as the CO2 produced. Thanks anyways.