Somebody please save me!!

[Leafs_Freak]

Hey guys, I am doing a lab right now and I am totally screwed. I need an 8 on this lab or I am going to fail the course!! I've never got more than a 6.7 from my teacher so I really need a hero!

 

We took lemon juice and put NaOH in with it and an indicator that made it go pink after average 4.37 mL of NaOH put in. It is 1.000 M NaOH.

 

Lemon Juice pH reading was 2.40

 

Tap water pH after 4 x 30 sec. of blowing through it with a straw was 6.12

 

1) "Write the balanced equation for the neutralization of citric acid using NaOH solution."

 

2) "What is the stoichiometric ratio between citric acid and NaOH"

 

3) "Calculate H+ molarity, [H+] in mol/L in the lemon juice based on the average titration volume and the stated molarity of the NaOH solution"

 

4)" Use the stoichiometric ratio to calculate the citric acid molarity (moles/Liter) of the lemon juice."

 

Guidelines for Discussion:

1. What should the pH of a pure sample of distilled, deionized water be?

 

2. Based on its measured pH, which of the following best describes the chemical nature of Sarnia tap- water? (pH is 7.23)

(a) acidic,

(b) slightly acidic

© neutral

(d) slightly basic

(e) basic

 

3. Name and write the formula of the chemical compound in Sarnia tap-water that is

causing the characteristic described in question 2. ?

 

 

4. Name and write the formula of the component of exhaled air that causes the pH of tap-water to decrease?

 

 

 

5. Write the chemical equation for the change mentioned in 4.

 

 

 

 

4. Write the formula of the gaseous chemical released by coal-fired generating stations and internal combustion engines that is primarily responsible for acid rain?

 

 

 

5. Convert the measured pH of the lemon juice into H+ molarity [H+] in mol/L

 

6. Compare the [H+] calculated in 5. with the [H+] determined on page 1. based on the titration?

 

Bonus

7. Show how the weak acid behaviour of citric acid can be used to explain the difference between the two H+ molarities stated in 6

[thedarkshade]

First we won't really give straight answers but only hints that would possibly lead you to the answer. I hope you will manage to get there somehow

 

1) Acids with bases give salts plus water is released (water is sometimes needed only to equalize the equation). Here's one example

 

[ce]HCl + NaOH -> NaCl + H2O[/ce]

 

When a strong acid reacts with a strong base you have a neutralization reaction since the pH will be 7, pH=7. This is the case on the reaction I posted above

When a strong acid reacts with a weak base, the pH<7, and so the medium will be acidic. (i.e. HCl + NH3).

And when a weak acid reacts with a strong base the pH>7, so the medium with be basic.

In your case you have a weak (organic) acid reaction with a strong base, so I guess you know why the pH is the way it is.

 

2) This will help you doing stoichiometry yourself:-)

 

3) You will need only (I guess) [math]c=\frac{n}{V}[/math] to do that. Or it would be better [math]c=\frac{m}{MV}[/math], which is the same thing.

[CaptainPanic]

4. When the pH decreases, this means that the water contains more acid. What is the biggest difference between inhaled and exhaled air?

[5614]

The most significant difference between inhaling and exhaling is that most of the oxygen we inhale is absorbed by our lungs, and so we don't exhale it, and that we do exhale CO₂, which is a waste product of the energy making processes which occurs inside our body.

 

Although the question doesn't ask, the beginning of the question talks about pH, so I guess I should point out that CO₂ is acidic.

[CharonY]

The most significant difference between inhaling and exhaling is that most of the oxygen we inhale is absorbed by our lungs, and so we don't exhale it, and that we do exhale CO2, which is a waste product of the energy making processes which occurs inside our body.

 

Hrmmms it is not really related to the the question, however the (human) lung only retains a small fraction of the O2. On average your breath contains ~15% O2 (with an average concentration of ~21% O2 in the atmosphere). But what really has an effect on pH is CO2 (which is an acidic oxide).

[thedarkshade]

4. When the pH decreases, this means that the water contains more acid.

Or said otherwise the solution is dominated by H+ ions.