Acids & Bases

Acids & Bases

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Litmus Test

• red - acid

• blue - base

• acid-base indicators

Acids and Metals & Carbonates

Acid-Base Theories

• Arrhenius - all acids contained H atoms that became H+ ions in water. Bases released OH- ions into water.

• Water will want to establish an equilibrium H+ ions react with OH- ions to form water molecules. Water molecules react to form H+ ions and OH- ions.

• But what about ammonia which acts as a base but does not contain the hydroxide ion?

• Bronsted theory - proposed that acids and bases be identified by their behavior in a reaction

Bronsted Theory

• A Bronsted acid is a proton (H+) donor

• A Bronsted base is a proton acceptor

Conjugate acid-base pairs

• There are two acids and two bases

• When an acid donates a H+, a base is left.

Multiple Choice

Identify the acid-base pairs in the reaction:

 $H_2O\ +\ HNO_3\ \Longleftrightarrow\ H_3O^+\ +\ NO_3^-$  

•  $HNO_3\ ,\ NO_3^-$  &   $H_2O\ ,\ H_3O^+$  
  
  

•  $H_2O\ ,\ HNO_3$   &   $H_3O^+\ ,\ NO_3^-$  

Multiple Choice

Identify the acid-base pairs in the following reaction:

 $H_2O\ +\ SO_4^{-2}\ \Longleftrightarrow\ HSO_4^-\ +\ OH^-$  

•  $H_2O\ ,\ OH^-$  &  $SO_4^{-2}\ \ ,\ HSO_4^-\ ^{ }$  

•  $H_2O\ ,\ SO_4^{-2}\$  &  $HSO_4^-\ ,\ OH^-$  

Multiple Choice

Identify the acid-base pairs in the following reaction:

 $H_2O\ +\ HSO_4^-\ \Longleftrightarrow\ OH^-\ +\ H_2SO_4$  

•  $\ OH^-\ ,\ H_2SO_4$  &  $H_2O\ ,\ HSO_4^-\$    

•  $H_2O\ ,\ OH^-\$  &   $\ HSO_4^-\ ,\ H_2SO_4$  

pH concept

• pH = "potential hydrogen" a measure of how many hydrogen ions exist in a solution.

• the pH scale is primarily from 0 to 14

• A neutral solution has a pH of 7

• acidic solutions (0 to 6.9)

• basic solutions (7.1 to 14)

Multiple Choice

Identify whether the substances is acidic, basic, or neutral based on pH:

tomatoes pH = 4.5

• acid

• base

• neutral

Multiple Choice

Identify whether the substances is acidic, basic, or neutral based on pH:

baking soda pH = 8.3

• acid

• base

• neutral

Multiple Choice

Identify whether the substances is acidic, basic, or neutral based on pH:

lemon juice pH = 2.0

• acid

• base

• neutral

Multiple Choice

Identify whether the substances is acidic, basic, or neutral based on pH:

water pH = 7.0

• acid

• base

• neutral

Open Ended

pH stands for __________ and is a measure of how many _________ exist in a solution. A neutral solution has a pH of ___. We can determine pH using indicators such as _________, _________, and litmus paper.

Open Ended

Name 5 properties of an acid:

Multiple Choice

All of the following are acids EXCEPT:

• $HCl$

• $HNO_3$

• $NaOH$

• $H_2SO_4$

Open Ended

Name 5 properties of bases:

Multiple Choice

All of the following are examples of bases EXCEPT:

• $CH_3COOH$

• $NaOH$

• $NH_3$

• $NaHCO_3$

Open Ended

Chemists often call a hydrogen ion a proton. Explain why an acid is sometimes called a proton donor, and a base is sometimes called a proton acceptor.

Strength of Acids

• Vinegar (acetic acid) great on salads, but using hydrochloric acid would be a bad idea.

• Maybe use it to clean bricks but not on food.

Strong Acids and Bases

• Acids and bases are classified into one of two categories depending on their strength, which is the degree to which they form ions.

• Strong - completely dissociate or ionize in water ( NaOH & HCl)

• Weak - produce few ions when dissolved in water

Strong base (NaOH)

Strong Acids

Weak Acids & Bases

Contains acids and bases with a wide range of strengths.

Most acids and bases fall into this category.

Only partially ionized

Weak Acids - Acetic acid

Ammonia - weak base

Weak is not insignificant

• Amino acids have properties of both weak acids & bases.

• The coiling of DNA is due to interactions between weak acids and bases.

Strength is not concentration

• The combination of strength and concentration determine the behavior of a solution

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Everyday Chemistry

• Shampoos with high pH make the entire hair shaft swell and push the cells of the cuticle away from the rest of the shaft

• Harsh basic solutions dissolve some of the cuticles, damaging the hair (like in dye)

• Acidic substances (low pH) make the hair shaft tight and smooth by shrinking it and causing the cells of the cuticle to lie flat.

• Low pH shampoos help restore damaged hair and

pH in skincare products

• brighter skin - high pH

• Remove top layer of keratin which removes dead cells and the new cells will look fresh and vibrant.

• Occasional use is ok, but regular use may damage health skin by removing too many layers

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Open Ended

If you live in an area where the water is hard, your hair may look dull. Why would rinsing with water to which lemon juice has been added help?

Open Ended

Why would a person with acne use skin products that are pH-neutral or mildly acidic?