Acid-base reactions

Terminology

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[[$\text{pH}$]] = a measurement scale indicating the amount of hydrogen ions [[$\text{H}^+$]] in a unit of solution. As an equation,
[[$$\text{pH} = -\text{log}\{\text{H}^+\}$$]]
and as s a simplified equation,
[[$$10^{\text{pH}} \approx \frac{\text{amount of solution in litres}}{\text{amount of H}^+\text{ ions}}.$$]]
acidic = a solution whose [[$\text{pH}$]] is below 7
neutral = a solution whose [[$\text{pH}$]] is 7
basic = a solution whose [[$\text{pH}$]] is above 7

an acid = a substance capable of donating a hydrogen ion [[$\text{H}^+$]]
a base = a substance capable of receiving a hydrogen ion [[$\text{H}^+$]]

All solutions of acids are acidic, and all solutions of bases are basic.

Measuring acidity

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Equipment:

2x 100 ml beaker

50 ml of water in each one
3 drops of BTB in each one

1x straw
1 bottle of [[$\text{HCl(aq)}$]]
1 bottle of [[$\text{NaOH(aq)}$]]
10 slips of pH paper
1 tissue

Instructions:

Pick either beaker.
Blow air into the liquid with a straw.

Caution! Do not inhale, just exhale.
Caution! Blow gently to prevent spills.

Observe the change.
Write the reaction as an equation.
- What is the substance you exhale?
- What is the substance you exhale into?
- What is the substance the reaction yields?
Switch to the unused beaker
Add 15 drops of [[$\text{HCl}$]] into the solution, one drop at a time.
Measure the pH of the solution with a slip of pH paper.
Place the slip on the tissue.
Add 3 drops of [[$\text{NaOH}$]] into the solution.
Repeat from step 7 onwards until the pH slips are exhausted.
Plot the pH changes as a diagram.
- horizontal: drops of [[$\text{NaOH}$]]
- vertical: pH of solution
- With a trendline, find the amount of [[$\text{NaOH}$]] drops needed for pH 7.

Measuring buffering ability

2018-10-18T14:29:52+03:00

Equipment:

100 ml beaker

20 ml of milk
3 drops of BTB

1 bottle of [[$\text{HCl(aq)}$]]
1 bottle of [[$\text{NaOH(aq)}$]]
10 slips of pH paper
1 tissue

Instructions:

Add 15 drops of [[$\text{HCl}$]] into the solution, one drop at a time.
Measure the pH of the solution with a slip of pH paper.
Place the slip on the tissue.
Add 3 drops of [[$\text{NaOH}$]] into the solution.
Repeat from step 1 onwards until the pH slips are exhausted.
Plot the pH changes as a diagram.
- horizontal: drops of [[$\text{NaOH}$]]
- vertical: pH of solution
- With a trendline, find the amount of [[$\text{NaOH}$]] drops needed for pH 7.

Examples

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Example. When mixed with water, hydrochloric acid [[$\text{HCl}$]] dissociates into hydrogen ions [[$\text{H}^+$]] and chloride ions [[$\text{Cl}^-$]]:
[[$$\text{HCl} \rightarrow \text{H}^+ + \text{Cl}^-$$]]
In this context, water acts as a base for the hydrochloric acid. Water molecules [[$\text{H}_2\text{O}$]] absorb the dissociated hydrogen ions [[$\text{H}^+$]] to yield hydronium ions [[$\text{H}_3\text{O}^+$]]:
[[$$\text{HCl} + \text{H}_2\text{O} \rightarrow \text{H}_3\text{O}^+ + \text{Cl}^-$$]]
Example.
When mixing water solutions of hydrochloric acid [[$\text{HCl}$]] and sodium hydroxide [[$\text{NaOH}$]], both ionic compounds dissociate into positive and negative ions:
[[$$\text{HCl} + \text{NaOH} \rightarrow \text{H}^+ + \text{Cl}^- + \text{Na}^+ +\text{OH}^-$$]]
In this context, the hydroxide in sodium hydroxide acts as the base for the hydrochloric acid. Each hydrochloric acid particle donates a hydrogen ion [[$\text{H}^+$]] to one sodium hydroxide particle. In simpler words, the acidic [[$\text{H}^+$]] and the basic [[$\text{OH}^-$]] combine to make water:
[[$$\text{H}^+ + \text{Cl}^- + \text{Na}^+ + \text{OH}^- \rightarrow \text{NaCl} + \text{H}_2\text{O}$$]]
As ions of opposite charge, the remaining sodium ions [[$\text{Na}^+$]] and chloride ions [[$\text{Cl}^-$]] associate to form sodium chloride [[$\text{NaCl}$]].

Metal hydroxides

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[[$2\text{Li}+2\text{H}_2\text{O}\rightarrow2\text{LiOH}+\text{H}_2$]]	lithium hydroxide [[$\text{LiOH}$]]
[[$2\text{Na}+2\text{H}_2\text{O}\rightarrow2\text{NaOH}+\text{H}_2$]]	sodium hydroxide [[$\text{NaOH}$]]
[[$\text{Ca}+\text{H}_2\text{O}\rightarrow\text{Ca(OH)}_2+\text{H}_2$]]	calcium hydroxide [[$\text{Ca(OH)}_2$]]
[[$\text{Mg}+\text{H}_2\text{O}\rightarrow\text{Mg(OH)}_2+\text{H}_2$]]	magnesium hydroxide [[$\text{Mg(OH)}_2$]]

Acids and their salts

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hydrochloric acid	[[$\text{HCl}$]]	-chloride
sulphuric acid	[[$\text{H}_2\text{SO}_4$]]	-sulphate
nitric acid	[[$\text{HNO}_3$]]	-nitrate
carbonic acid	[[$\text{H}_2\text{CO}_3$]]	-carbonate
phosphoric acid	[[$\text{H}_3\text{PO}_4$]]	-phosphate

Example.
a. hydrochloric acid + lithium hydroxide [[$\rightarrow$]] lithium chloride + water
[[$$\text{HCl} + \text{LiOH} \rightarrow \text{LiCl} + \text{H}_2$$]]
b. sulphuric acid + calcium hydroxide [[$\rightarrow$]] calcium sulphate + water
[[$$\text{H}_2\text{SO}_4 + \text{Ca(OH)}_2 \rightarrow \text{CaSO}_4 + 2\text{H}_2\text{O}$$]]

Tutkijat palasivat maailman suurimmasta merenalaisesta montusta ja kertoivat ennennäkemättömistä tippukivistä ja ”hullusta” rikkivetykerroksesta

"Hapeton rikkivetykerros ei päästä läpi edes valoa."

Read the article and put your chemistry knowledge to the test by answering the following questions:
- What is the composition of the lowermost layer of the ocean described in the article?
- Under less extreme conditions, which substance would dissolving sulfur oxide into water yield?

Ammonia pollution damaging more than 60% of UK land – report

When prompted, create a mind map that summarizes the properties of ammonia told in the news article.

Test for yourself!

2019-10-30T09:39:10+02:00

Using the "My solution" section of the applet tinyurl.com/valacidsim, answer the following questions:

Acids

What are the light grey molecules?

What are the red ions?

How does the initial concentration of acid in the solution (more mol/L, or particles per litre) affect the pH of your solution?

How does the strength of your acid affect the amount of grey molecules?

How does the strength of your acid affect the pH of your solution?

How does the strength of your acid affect the conductivity of your solution?

Bases

What are the blue ions?

How does the initial concentration of base in the solution (more mol/L, or particles per litre) affect the pH of your solution?

How does the strength of your base affect the amount of grey molecules?

How does the strength of your base affect the pH of your solution?

How does the strength of your base affect the conductivity of your solution?