<< Chapter < Page Chapter >> Page >

The idea of mole concept is simple. It neatly relates various reactants and products in the ratio of whole numbers. There is, however, one hitch in applying this concept. The reactants or products may not necessarily be participating in its pure form. Consider the reaction :

M g + 2 H C l M g C l 2 + H 2

Here, magnesium is used in its pure solid form. The hydrogen gas is evolved in pure gaseous form. On the other hand, Hydrochloric acid is used as a solution of a specific concentration in water.

Thus, magnesium and hydrogen exist in pure form. We can find moles of solid magnesium by using its molecular weight. Similarly, we can determine moles of pure hydrogen gas using Avogadro’s hypothesis. In the case of hydrochloric acid, however, the acid in the form of solute participates in reaction – not the solvent i.e. water. Clearly, we need to find a way to connect the concentration of HCl to mass or moles. In this module, we shall exactly do the same by defining different concentration terms of the solution and its relation with mass or moles of the solute as involved in the reaction.

Solution
A solution is a homogeneous mixture of two or more components. The substance present in smaller proportions is called solute and the substance in larger proportion is called the solvent.

Solution comprises of solute and solvent. In expressing concentration of solution, we make use of the fact that mass is conserved,

Mass of solution W S = Mass of solute W B + Mass of solvent W A

The concentration, however, need not be necessarily expressed in terms of mass (w). We may choose volume (v) also depending upon measuring convenience. Sometime, we may express concentration as combination of mass (w) and volume (v).

Concentration of a solution is basically measurement of solute (B) with respect to solution(S) or solvent(A). With the only exception of molality, concentration is expressed as a comparison of the quantity of solute (B) to that of solution (A+B). In the case of molality, it is comparison of solute (B) to that of solvent (A). Further, this comparative ratio is either a number or percentage (%).

There are large numbers of concentration measuring terms. They are basically classified under following three categories :

  • Measurement based on mass/volume : mass percentage (w/w), volume percentage (v/v), strength of solution (w/v)
  • Measurement based on molecular weight (moles) : molarity (M), molality (m)
  • Measurement based on equivalent weight (gram - equivalents) : normality (N)

Measurements based on mass/volume

Mass percentage (w/w)

The mass percentage is expressed as :

Mass percentage x = Mass of solute B Mass of solution A + B X 100

Mass percentage x = W B W S X 100 = W B W A + W B X 100

If we measure mass in grams, we can rewrite the expression :

Mass percentage x = g B g S X 100 = g B g A + g B X 100

Sometimes, we may opt to express concentration simply as fraction. In this case, we are not required to multiply ratio by 100,

Mass fraction = W B W A + W B = g B g A + g B

Problem : One litre of oxalic acid of density 1.08 gm/cc contains 3.24 gm of oxalic acid. Find its mass percentage.

Solution : The mass of solute (oxalic acid) is given. We need to find the mass of the solution to determine mass percentage.

g S = V S X ρ S = 1000 X 1.08 = 1080 g m

Mass percentage x = g B g A + g B X 100 = 3.28 1008 X 100 = 0.3

Questions & Answers

a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
im not good at math so would this help me
Rachael Reply
how did I we'll learn this
Noor Reply
f(x)= 2|x+5| find f(-6)
Prince Reply
f(n)= 2n + 1
Samantha Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Got questions? Join the online conversation and get instant answers!
QuizOver.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Stoichiometry. OpenStax CNX. Jul 05, 2008 Download for free at http://cnx.org/content/col10540/1.7
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Stoichiometry' conversation and receive update notifications?

Ask