Properties of acids and bases
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PROPERTIES OF ACIDS AND BASES. Acids. taste sour or tart (vinegar, lemons) aqueous solutions of acids are electrolytes cause indicators to change colors many metals react with acids to produce H 2 gas react with hydroxides to form a salt and water

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PROPERTIES OF ACIDS AND BASES

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PROPERTIES OF ACIDS AND BASES


Acids

  • taste sour or tart (vinegar, lemons)

  • aqueous solutions of acids are electrolytes

  • cause indicators to change colors

  • many metals react with acids to produce H2 gas

  • react with hydroxides to form a salt and water

  • most formulas begin with H.

  • pH < 7, pOH > 7

  • [H3O+] > 1.0 x 10-7, [OH-] < 1.0 x 10-7

  • produce H3O+ (aka H+) ions in water solutions


Common uses of acids

  • HNO3 or HCl are used for etching metals.

  • HF is used for etching glass.


Bases

  • bitter taste (soap, unsweetened chocolate)

  • bases are electrolytes in aqueous solution

  • cause indicators to change colors

  • feel slippery

  • react with acids to form a salt and water

  • often contain OH- , or ammonia NH3

  • pH > 7, pOH < 7

  • [H3O+] < 1.0 x 10-7, [OH-] > 1.0 x 10-7

  • produce OH- ions in water solutions


  • hydroxide ion (OH-)

    • formed when a water molecule loses a H+

  • hydronium ion (H3O+)

    • formed when a water molecule gains a H+

      H2O + H+ H3O+

      *your text uses H+ and H3O+ interchangeably*


Acidic solutions

[H3O+] > [OH-]

[H3O+] > 1.0 x 10-7

Basic solutions

[OH-] > [H3O+]

[OH-] > 1.0 x 10-7

[H3O+] < 1.0 x 10-7


Acidic or Basic?

  • [H3O+] = 1 x 10-3

  • [H3O+] = 1 x 10-11

  • [OH-] = 1 x 10-4

  • [OH-] = 1 x 10-13

H+ > 1.0 x 10-7

Acidic

Basic

H+ < 1.0 x 10-7

OH- > 1.0 x 10-7

Basic

[H3O+] = 1 x 10-10

OH- < 1.0 x 10-7

Acidic

[H3O+] = 1 x 10-1


pH Concept:

pH = - log [H3O+] or - log [H+]

  • A logarithm (log) is the exponent to which 10 must be raised to get the number.

  • logbasevalue = exponent

  • If X = 10Y, then log10 X = Y

  • In calculator enter:

    - log (value)


Example:

log 101 = 1

log 10-5 = -5

If [H3O+] = 1.0 x 10-4

pH = - log [H3O+]

then pH = -log [1.0 x 10-4]

= 4.00


pH problems:

What is the pH if:

[H3O+] = 1 x 10-5pH = __________

pH = - log [H3O+]

[H3O+] = 1 x 10-13pH = __________

pH = - log [H3O+]

pH > 7 is basic

pH < 7 is acidic

pH = 7 is neutral

5

Acidic

13

Basic


pOH = -log [OH-]

What is the pOH if:

[OH-] = 1 x 10-4pOH =

pOH = -log [OH-]

[OH-] = 1 x 10-3pOH =

pOH = -log [OH-]

4

Basic

3

Basic


pH + pOH = 14

pH = 6pOH =

pH = 4pOH =

pOH = 3pH =

pOH = 11pH =

8

10

11

3


Calculator:

10x (-pH.)

[H3O+] = antilog (-pH)[OH-] = antilog (-pOH)

  • pH = 7.00so[H3O+] =

    [H3O+] = antilog (-7.00)

  • pH = 3.00[H3O+] =

    [H3O+] = antilog (-3.00)

  • pOH = 8.00[OH-] =

    [H3O+] =

    [OH-] = antilog (-8.00)

    14 = 8 + xx = 6

1.0 x 10-7

1.0 x 10-3

1.0 x 10-8

1.0 x 10-6


Using a programmable calculator for pH:

What is the pH if [H3O+] = 5.2 x 10-2

pH = - log (H3O+)

pH = (-) log (5.2 x 10-2)

- log10 (5.2 x10-2) enter

pH =

1.3


Using a programmable calculator for antilogs:

What is the [H3O+] if the pH is 4.92?

[H3O+] = antilog (-pH)

[H3O+] = antilog (-4.92)

Calculator:

10x (- 4.92) Enter

[H3O+] =

10x is the 2nd function of the log key

1.2 x 10-5


Example:

  • pH = 9.29 [H3O+] = ?

  • [H3O+] = antilog (-pH)

  • [H3O+] = antilog (-9.29)

  • Calculator:

  • 10x(-9.29) Enter

  • [H3O+] = 5.13 x 10-10


Indicators

  • Indicators are substances that change color in solutions of different pH.

  • Indicators are usually weak acids.

  • They are one color in their acid form and a different color in their base form.

  • HIn  H+ + In-

  • Help determine approximate pH


Indicators cont.

phenolphthalein

  • colorless in acid

  • pink in base

  • changes at pH 8.0 -10.0


Indicators cont.

litmus

  • blue litmus turns red in acid

  • red turns blue in base

    universal indicator

  • mixture of indicators

  • changes into different colors at each pH (rainbow colors)


Indicators cont.

bromothymol blue

  • blue in basic solutions

  • yellow in acidic solutions

  • green in neutral solutions


Common acidsCommon bases

HClNaOH

HNO3 KOH

H2SO4Ca(OH)2

H3PO4Mg(OH)2

HC2H3O2NH3

H2CO3


Acid-Base Reactions

  • When acids and bases react, the products most commonly formed are water and a salt (ionic compound).

  • This is called a neutralizationreaction.


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