Volumetric

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Soln

200cm3 of solution contain 2.65g of Na2CO3

1000cm3 of soln will contain X

X = 1000cm3 x 2.65g

200cm3 X = 13.3g

Simple arithetic!

Remember 1dm3 = 1000cm3

Slide 10

Alternatively

You can use this formula:

Mass conc = mass(g)/vol(dm3)

[can you remember?]

Mass = 2.65g(given), Vol in dm3 = 200

1000

= 0.200dm3

.: mass conc = 2.65

0.200

=13.25gdm3

Slide 11

One more

What is the molar conc. of a solution containing 1.12g of potassium hydroxide in 250cm3 of solution? [KOH = 56]

Hint: molar conc. means ??????????

Conc. in mole per dm3

Get your answer in gdm-3 and convert it to

moldm-3

Then you’ve solved the problem

Slide 12

Now let’s do it

250cm3 contain 1.12g

1000cm3 will contain X

X = 1000 x 1.12

250

X = 4.48gdm-3

Convert to molar conc.

Molarity = mass conc molarmass

= 4.48/56

= 0.080mol/dm3

Using formular

Molar conc = amnt (mol)

Vol(dm3)

Mole = mass/Mm

= 1.12/56 = 0.020mol

Vol (dm3) = 250/1000 = 0.250dm3

Molar conc. = 0.020

0.250

= 0.080 mol/dm3

Slide 13

More examples

What mass of sodium hydrogen trioxocarbonate (iv) NaHCO3 would be required to prepare 100cm3 of 2.0 molar solution? [NaHCO3 = 84]

Remember

Molar means mol/dm3

i.e. what mass is needed to prepare 2mol/dm3

You can solve it in mol & then convert it to mass.

OR

Convert the given mol/dm3 to gdm3 and solve the problem.

Slide 14

Have a look!

2molar soln means ????? 2mol/dm3

1000cm3 of the soln contain 2mol NaHCO3

100cm3 will contain X

X = 100 X 2 = 0.2mol

1000

Convert to mass:

Mass of NaHCO3 required = 0.2 X 84

= 16.8g

Slide 15

PRActice problems

Slide 16

Principle of dillution (dillution factor)

Key Concepts

The concentration of a solution is usually given in moles per dm-3 (mol dm-3 OR mol/dm3).

This is also known as molarity.

Concentration, or Molarity, is given the symbol C.

A short way to write that the concentration of a solution of hydrochloric acid is 0.01 mol/L is to write [HCl]=0.01M

The square brackets around the substance indicate concentration.

The solute is the substance which dissolves.

The solvent is the liquid which does the dissolving.