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12 Chemistry -- Volumetric Analysis

Whenever a solution gives ppt,does the Normality/Molarity of a solution changes?

It's not necessary for a substance to change it's normality as it is volume and mass dependent. Until and unless any external substances are added to a solution, it's unlikely for the solution to change it's normality/molarity.

Define Decinormal Solution.

The solution containing 1/10 (one tenth) of one gram equivalent weight of substance dissolved in 1 litre of volume is called decinormal solution. It is represented as N/10 or 0.1N .

What are the requisites for a substance to be a primary standard?

The requisites for a substance to be a primary solution are:

  • It should be in available in pure state ,
  • Its composition should be constant during storage and weighing,
  • It should be readily soluble in water and not be decomposed by water,
  • It should have high equivalent weight and should not be hygroscopic or deliquescent.

Write an example of redox titration. Why is it called so?

An example of redox titration is titration of oxalic acid solution against KMno4solution in acidic medium.

It is called so because ,during titration ,oxidation occur on one of the species and reduction on the other species, making it redox reaction and thus redox titration.

Calculate the mass of oxalic acid required to prepare its 250 ml of N/10 solution.

Solution:

Molecular weight of oxalic acid= 126

Equivalent weight of oxalic acid =63

Volume of solution to be prepared ,V =250ml

Conc.of solution to be prepared, N=0.1N

Now ,

We have

Mass of oxalic acid (g)=Equivalent weight volume normality 1000

= 632500.11000

1.575g

What volume of water should be added to 50ml of N/2 NaOH to make it exactly decinormal?

solution:

volume v1= 50ml

concentration n1= 0.5N

volume v2=?

concentration n2=o.1N

Now we have

molar equivalent of seminormal solution= molar equivalent of deci normal solution

or, 0.5* 50= 0.1*v

or, 250= v

Thus, volume of water should be added=250-50 =200 ml

What Are The Differences Between End Point And Equivalence Point?

The main difference between equivalence and endpoint is thatthe equivalence point is a point where the chemical reaction comes to an end while the endpoint is the point where the colour change occurs in a system.

Oxalic acid is taken as a primary standard solution. Why?

oxalic acid is taken as primary standard solution because it is highly stable as it is weak acid and can be obtained in pure form. also because it is non-hygroscopic, non- deliquescent and hass high molecular mass which leads to less error and highly precise data can be observed.



Distinguish between decinormal and decimolar solution.

Deci- Normal solution ---->The solution containing 1/10 mole of solute in 1 liter of solution is called normal solution.

Deci-molar solution(M10):The solution containing 110 th mole of solute in 1 liter of solution is known as decinormal solution.

Difference between molarity and normality.


Normality Molarity
1. It is the number of gram equivalents of solute dissolved per litre solution. 1. It is the number of gram molecules of solute dissolved per litre its solution.
2. In general, Normality(N) = (g/L)/eq. wt 2. Molarity(M) = (w*1000)/(v* mol. wt)



What is the normality of 20cc of 2M phosphoric acid (H3PO4)?

Normality = Molarity x n

here N is acidity for base and basicity for acid.

so Normality = 2 x 3

since H3PO4 has 3 displaceable hydrogen.

Normality = 6 N

What do you mean by the equivalent weight of an element?

equivalent weight is the weight of a substance especially in grams that combines with or is chemically equivalentto eight grams of oxygen or one gram of hydrogen.

Define the molarity of a solution. Calculate the molarity of one liter of 93% H2SO4 solution (weight by volume). The density of the solution is 1.84 g/mL.

The number of moles of a solute dissolved in 1 L (1000 ml) of the solutionis known as the molarity of the solution.

we know,

Molarity * mol. wt = %(w/v) * 10

Molarity = 93*10/98 ==> 9.489


"All standard solutions are not primary standard solutions." Comment the statement.

No, they are not. A primary standard is a reagent that is extremely pure,stable,has no waters of hydration and has high molecular weight.Lots of standard solutions are only secondary standard solutions because their concentration changes with time or because it is impossible to produce the exact concentration.

How many mL of a 0.1 M HCl are required to react completely with a 1gm mixture of Na2CO3 and NaHCO3 containing the equimolar amount of the two.

solution:let, the amount of Na2Co3 in the mixture = x gmNaHCo3 present in mixture = (1-x) gmMolar mass of Na2Co3 = 2*23+12+3*16 = 106 gm/molesimilarly, molar mass of NaHCo3 = 84 gm/moletherefore, moles of Na2Co3 in x gm = x/106 and moles of NaHCo3 in (1-x) gm = (1-x)/84According to the question,x/106 = (1-x)/84 so, x = 0.558gmThus the number of moles of Na2Co3 and NaHCo3 are 0.00526 moleAgain by reaction,


Na2CO3+2HCl2NaCl+H2O+CO2

Na2CO3+2HCl2NaCl+H2O+CO2
NaHCO3+HClNaCl+H2O+CO21 mole ofNa2CO3
...

It is better to express the concentration in molality rather than molarity. why?

Mathematically,

Molality = mol / kg

Molarity = mol/ liter

it means that Molality solely depends upon the mass of solution and solute but molarity takes measurement with respect to volume of the solution.

we know that volume is temperature dependent quantity i.e. volume varies with temperature and has direct relation but in contrast there is no effect of temperature or any other quantity in mass. Since the difference in temperature can trigger the preciseness in expressing concentrations, it is...

What is meant by the normality factor?

In titration, normality factor is the ratio of the amount of substance taken to the amount of substance to be taken to prepare a standard solution.

It is also taken as the ratio of experimental weight to the theoretical weight of the amount of substance with respect to preparation of solution.

Define the term titration error.

Titration error is defined as the difference between the measured endpoint and equivalence point of the titration

What is meant by the acidity of the base?

The acidity of base is the number of monobasic acid(s), required to neutralize one molecule of the base.

In other words, it is the number of replaceable OH group(s) present in the base.


What is meant by acidimetry?

The process of determination of the strength of acids by carrying out neutralization titration with standard alkali is called acidimetry.

1).The number of gram equivalents of a solute dissolved per liter of solution is

2).'M' is the molecular mass of KMnO4. The equivalent weight of KMnO4when it is converted into K2MnO4 is

3).Normality of 2M H2SO4 is

4). The solution of sulphuric acid contains 80% by weight of H2SO4. Specific gravity of this solution is 1.71.Its normality is about

5). Phenolphthalein is a

6). The indicator used in the titration of iodine against sodium thiosulphate is

7). Indicators used in acid base titration are

8). Which indicator can be used in the titration of strong acid and strong base?

9). The indicator used in titration of oxalic acid with caustic soda is

10). Methyl orange gives red colour in 

11). The range of phenolphthalein as an indicator is in between PH 

12). Starch can be used as an indicator for the detection of traces of 

13). In the reaction NaOH + H3PO4 --------->NaH2PO4 + H2. The equivalent weight of phosphoric acid(H3PO4) is 

14). Equivalent weight of an acid is equal to 

15). The pink colour of phenolphthalein in alkaline medium is due to 

16).Approximately atomic weight of an element is 26.89. If its equivalent weight is 8.9,the exact atomic weight of element would be

17). Acidified potassium permanganate  solution is decolourised by

18). If M is molecular weight of KMnO4, equivalent weight of KMnO4 in acidic medium is

19). When KMnO4 is reduced with oxalic acid in acidic medium the oxidation number of Mn changes from?

20). 0.16g of dibasic acid required 25 ml of decinormal NaOH solution for complete neutralization. The molecular weight of the acid will be 

21). 74.5 gm of a metallic chloride contains 35.5 gm of chlorine, the equivalent weight of the metal is 

22). If the wt. of metal and chlorine in a metal chloride is in the ratio of 1:2, the equivalent weight of the metal is

23). When volume of water is to be added to 150 ml of 0.2 N Na2CO3 solution to make it 0.05 N ?

24). The volume of 0.1 M H2SO4 that is needed to completely neutralize 40 ml of 0.2 M NaOH is 

25). The normality of 10% NaOH solution is

26). 0.4 gm of NaOH is added to 10 ml of 1N HCl, the resulting solution is 

27). When 50 ml of HCl reacts with 10 gm of CaCO3, normality of the solution is

28). 0.45 gm of acid of molecular weight 90 was neutralized by 20 ml of 0.5N caustic potash. The basicity of the acid is

29). How much NaOH is required to neutralize 1500cm3 of 0.1NHCl?

30). 200 ml of 0.2 M HCl is neutralized with 0.1 M NaOH. Then during their half neutralization, what will be the molarity of HCl?

2M Na2CO3 is equal to its normality

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