Solutions to p47

1.†††††††† How do you tell acids from bases using litmus?

With red litmus, an acid will cause it to remain red, but a base will turn it blue.

With blue litmus, an acid will turn it red, but a base will cause it to remain blue.

2.†††††††† How can taste be used to distinguish between non-poisonous acids and bases?

Bases taste bitter (taste baking soda, for example).

Acids are sour, like lemons.

3.†††††††† How can a blind person tell a poisonous acid from a poisonous base?

Add Mg to both. Only the acid will cause a fizzing sound.

4.†††††††† What popular beverage turns colour in the presence of acid?

Tea. Itíll turn orange in the presence of acid.

5.†††††††† What kind of substance produces OH- in solution?

Bases.

6.†††††††† Complete the following ionic equations:

a.†††††††† HCl H+ + Cl-

b.†††††††† NaOH Na+ + OH-

c.†††††††† Ca(OH)2 Ca+2 + 2OH-1

d.†††††††† H2C2O4 2H+ + C2O4-2

7.†††††††† The table shows a number of chemical substances. Name them and identify the acids, bases and salts by placing an 'X' in the appropriate box.

FORMULAS

NAME of SUBSTANCES

ACID

BASE

SALT

NaOH

Sodium hydroxide

 

X

 

H2SO4

Sulphuric acid

X

   

MgBr2

Magnesium bromide

   

X

PbCO3

Lead(II) carbonate

     

HNO3

Nitric acid

X

   

CuBr

Copper (I) bromide

   

X

Ca(OH)2

Calcium hydroxide

 

X

 

HCl

Hydrochloric acid

X

   

NaCl

Sodium chloride

   

X

Al(OH)3

Aluminum hydroxide

 

X

 
 

Windex window cleaner

 

X

 
 

The content of citrus foods

X

   
 

Potassium iodide

   

X

7.†††††††† Give three everyday examples of neutralization reactions.

(1)             (1)                Limestone in soil neutralizes acidic precipitation.

(2)             (2)                Antacid tablets neutralize excess stomach acid.

(3)             (3)                Spermine from semen neutralizes acid from vaginal secretions.

8.†††††††† Fill in the blank:†††††††††† NaOH + HF --> H2O + NaF

p49 answers

Exercises

1.†††††††† a)†††††††† List three everyday solutions or substances with a pH < 7.

††††††††††† Toilet bowl cleaner; wine; soft drinks, juice

b)†††††††† Do the same for pH > 7.

Windex with ammonia, soap, toothpaste, baking soda, ocean water

2.†††††††† List three substances that can have a pH of exactly 7. What do these substances have in common?

††††††††††† Some salts, distilled water, milk

††††††††††† They are neither acidic nor basic

3.†††††††† How much more acidic is a pH 4 solution compared to a pH = 6 solution?

††††††††††† 106-4 = 100 times

4.†††††††† How much more basic is a pH 11 solution compared to a pH = 9 solution?

1011-9 = 100 times

5.†††††††† What could you do to lower the pH of soil?

††††††††††† Add acid

6.†††††††† What could you do to raise the pH of an acidified lake?

††††††††††† Add base

Answers to Examples  p46

1.         Classify as acid or base

a.         vinegar__A___

b.         drano____B__

c.         NaOH  ____B_

d.         HCl____A__

e.         pH = 3___A___

f.          pH = 5___A___

g.         pH = 8 ____B__

h.         A solution which turns blue litmus red___A__

i.          An electrolyte that is corrosive but which will not react with Mg to release hydrogen gas___B__

j.          A bitter-tasting substance___B___

 

2.         Complete the following ionic equations:

a.         HBr àH+ + Br-

b.         KOH àK+ + OH-