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Acids&bases.

posted Jul 23, 2016, 10:50 PM by Upali Salpadoru   [ updated Aug 30, 2017, 11:30 PM ]
     
Fig.1. Litmus test for acids.
Warning:-  
1.Handling concentrated acids and strong Alkalis is a dangerous task.  
2. Never taste a lab chemical.
3. Never add water to a concentrated acids. (Acids have to be added to water)

What is an acid test?
This originated from the using of nitricacid to test for  gold. It may also mean using of litmus to recognize acids. Now it has taken a wider meaning.
What are acids?                                      
In chemistry an acid is a compound that can produce Hydrogen ions, H+ in excess when dissolved in water. 
An acid is  a proton donor.

This chart will help you to recognize acids , bases and salts..
Chart no.1. Strong Acids,  and their salts.
   
  Chart no.1. Strong Acids,  and their salts.
  • Acids are printed in red while the alkalis are blue.
  • It is your task to get the formulae of the respective salts.
  • If you have any difficulty in deriving the formalae  please click Atoms and Molecules.
 These acids are sometimes called 'Mineral aciids'. They are strong, ionise well producing lot of H+.
  This is how  they ionize.     
  HCl H+ + Cl- .  
                           HNO3    H+   +  NO3-.     
                                                           H2SO4 → H+ +SO4-
What are Bases?

GCSE bite size BBC defines a bases as:-

"Substances that can react with acids and neutralise them to make a salt and water are called bases." 

A base is a proton acceptor.

 Chart. 2.  Salts of weak acids.  

Ions

HCOO-

Formate

CH3COO-

Acetate

S2-

Sulphide

CO32-

Carbonate

PO43-

Phosphate

H+

HCOOH

Forrmic acid

CH3COOH

Acetic acid

H2S

Hydrogen sulphide

H2CO3

Carbonic acid

H3PO4

Phosphoric acid

Na +

HCOONa

CH3COONa

Na2S

Na2CO3

 

K+

HCOOK

CH3COOK

K2S

K2CO3

 

Mg 2+

Mg(HCOO)2

Mg(CH3COO)2

MgS

MgCO3

 

Al3+

Al(HCOO)3 

Al(CH3COO)3

Al2S3

Al2(CO3)3

 

Zn2+

Zn(HCOO)2

Zn(CH3COO)2

ZnS

ZnCO3

 

Fe2+

Fe(HCOO)2

Fe(CH3COO)2

FeS

FeCO3

 

Pb 2+

Pb(HCOO)2

Pb(CH3COO)2

PbS

PbCO3

 

NH4+

HCOONH4

CH3COONH4

NH4S

(NH4)2CO3

 

Last column is left blank for you to practice.

A few important facts to remember with regard to properties of chemicals.

1. If the name of an element ends with "ium" it has to be a metallic element. 

     (Exception-Helium and mmonium)

2. All the salts of the alkali metals (Li,Na,K ) and ammonium are soluble in water.

3.All nitrates, acetates, and chlorates are soluble in water.

4. All chlorides are soluble except that of silver, mercury and lead.

 5. All sulphates are soluble except that of Barium, Strontium, Calcium, Lead, and Mercury (I).

6. All  carbonates, hydroxides, oxides, silicates, and phosphates of heavy metals are generally insoluble or slightly soluble.

______________________________________...

  Common Properties of Acids, Bases  and Salts.

  1. WARNING No lab chemical should ever be  tasted.

ACIDS

BASES

SALTS

  1. Sour taste.

  2. Corrosive.

  3. Turns blue litmus red.

  4. pH = 0- 7.

  5. Gives CO2 with carbonates.

  6. Neutralize bases.

  7. Dil. acids give H2 with some metals.

  1. Soapy taste.

  2. Feels slippery.

  3. Turns red litmus blue.

  4. pH =  7-14.

  5. Neutralize acids.

  6. Gives H2 with a few metals. (Al)

  1. Differs.

  2. Most are soluble in H2O.

  3. Solids. (Crystaline)

  4. Normal salts do not change the colour of litmus.

  5. pH = 7.

  6. Usually ionise.

Produce H+ ions in excess.

Produce OH- ions in aqueous solutions.

Exist as ions.



 Strong Acids and Bases neutralize each other to produce water and ionic compounds termed salts .
  As the ions of salts remain in ionic form, really what happens is only the formation of water.
     H+  + OH-   =  H2O
A few examples of acid base reactions.
 H+Cl- + Na+ + OH-   →   Na+  + Cl-H2O  Water does not ionise as much as the others.
 H+ +H+ + SO42-+  K+OH- +  K+ + OH- →  K+ K+ + SO42+H2O
 2H+ + 2NO3-  + Ca2++ 2OH-  → Ca2+ + 2NO3-  +H2O
 2HCl  + MgO     MgCl2 +  H2O

Acid Base Indicators.
These are a substances used to determine the acidity or basicity of a substance.


Indicators from kitchen and garden.

Substance

With Acids

With Alkalis

Beet root.

Red

Purple

Black berries & blue.

Red

Blue to violet.

Blue grapes

Deep red

Violet

Cherries

Bright red

Purple to blue.

Curcumin / turmeric

(curry powder)

Red ( pH below 8.6)

Yellow.

Geranium petals(Pelargonin)

Orange

Light blue

Morning glory

Reddish purple pH=6.6

Blue at pH=7.7

Onion (red)

Light red (strong smell)

Green  ( Low smell)

Petunia petals

Red

Violet

Red cabbage.

pH colours.

pH value

cabbage.jpg

Shoe flower

Red

Green

 

It worth trying out these also.

carrot juice, cranberry, Red radish, Rhubars, Strawberry,Tea, Food colouring.

pH pondus hydrogenii

This is a way to express the H+ concentration using logarithms.

"A measure of the degree to which a solution is acidic or alkaline.

An acid is a substance that can give up a hydrogen ion (H+);

A base is a substance that can accept H+.

The more acidic a solution the greater the hydrogen ion concentration and the lower the pH; a pH of 7.0 indicates neutrality,"

  Courtsey The free dictionary


Universal Indicator (Solution or Paper) gives a value by the colour change to get the acidity of a substance.

 

Mehara.jpg

Is Vinegar an acid?

Why is it?

Ali.jpg

                    Yes and No.

 It is an acidic substance not a pure acid or even a dilute acid.

Having an acidic or an alkaline property will not make a mixture an acid or an alkali.


Q.1.0
Classify these as:-Acids,  Acidic,  Alkali, Alkaline,  Salts, & others.
HCl      PbCl2       Water        Slaked lime(aq)    Soda water     Gastric juice  Vinegar Saliva      CuSO4        Na2CO3                      Lime juice      H3PO4         H2S,             Wax,         Oil           HNO3          NaOH          NH4OH              NaCl             Soap

 Marks  20.  

Q.2.0

 2.1

Ion

Salts

H+

HCl

HNO3

H2SO4

H2CO3

Cu2+

Hg2+

Ag+

NH4+

Fe3+

 

 

 

 


1.       2.2  Give the formulae of salts formed by the acids marked in red and the ions in the first column.  

5 x4 = 20.

2.      2.3 Which ion gives  blue or bluish coloured salts.                                                                                       5

3.      2.4 Which ion give thermally unstable salts.                                                                                                 5

4.      2.5 Name the following:-

a.       A soluble carbonate      b. c.  Insoluble chloride.                                 5x2   = 10     =  30 




Q.3.0

Complete these equations.

 1.     KOH  HCl  →  H2O +  ................

 2.   H2SO4 +  Ca(OH)2 → CaSO4 + ..............

 3.  ...........+HNO3  NH4NO3   + H2O

 4,  MgO  + ...........→ MgCl2    + H2O

  5.  NH4OH  +  ............→    (NH4)2CO3    + H2O

marks.4x5 =20


Q.4.0

1. A solution was tested with blue litmus paper. The colour did not change. What is your observation?

a. Alkaline solution.  b. Acid solution.  c. Neutral solution. d. Alkaline or neutral solution.

2. Half a tea spoon of lime was added to a beaker of pure water. A milky colour resulted. On filtering that there was a white residue. What is your observation with regard to solubility of lime?

a. Insoluble. b. Soluble. c. Either slightly soluble or insoluble.  d. Slightly soluble.

3. Most inorganic compounds contain hydrogen are acids. Yet water does not conform to that rule. What could be the reason?

a. Water has OH- ions to cancel that of H+ ions.           b. Water does not conduct current.

c. Water is a neutral substance.                                      e.  It has no sour taste.

4. Which is correct with regard to the oxides of non metals.

   a. They are solids.    b.  They dissolve in water to form alkalis.     c. They dissolve to form acids.

   d. They dissolve to form acids.

5. In case of an acid spill, which substance is NOT suitable for use as a neutralizing agent.?

a. Sodium hydroxide.    .b. Sodium carbonate.   c. Sodium bi carbonate.   d. Lime water.

 Marks 2x5 = 10.

1.   d.    2.  c    3. a.   4.  c.      5. a.

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