11.106

SECTION

11

11.7

LABORATORY SOLUTIONS

TABLE 11.47

Concentrations of Commonly Used Acids and Bases

Freshly opened bottles of these reagents are generally of the concentrations indicated in the table. This may not

be true of bottles long opened and this is especially true of ammonium hydroxide, which rapidly loses its strength.

In preparing volumetric solutions, it is well to be on the safe side and take a little more than the calculated

volume of the concentrated reagent, since it is much easier to dilute a concentrated solution than to strengthen

one that is too weak.

A concentrated C.P. reagent usually comes to the laboratory in a bottle having a label which states its

molecular weight

w , its density (or its specific gravity)

d , and its percentage assay

p . When such a reagent is

used to prepare an aqueous solution of desired molarity

M , a convenient formula to employ is

V

100wM

pd

where V

is the number of milliliters of concentrated reagent required for 1 liter of the dilute solution.

Example:

Sulfuric acid has the molecular weight 98.08. If the concentrated acid assays 95.5% and has the

specific gravity 1.84, the volume required for 1 liter of a 0.1 molar solution is

V

100 98.08 0.1 5.58 mL

95.5 1.84

Formula

Density,

Weight %

Reagent

Weight

g · mL

1 (20 C)

(approx)

Molarity

V, mL*

Acetic acid

60.05

1.05

99.8

17.45

57.3

Ammonium hydroxide

35.05

0.90

56.6

14.53

60.0

(as NH

3 )

17.03

28.0

Ethylenediamine

60.10

0.899

100

15.0

66.7

Formic acid

46.03

1.20

90.5

23.6

42.5

Hydrazine

32.05

1.011

95

30.0

33.3

Hydriodic acid

127.91

1.70

57

7.6

132

Hydrobromic acid

80.92

1.49

48

8.84

113

Hydrochloric acid

36.46

1.19

37.2

12.1

82.5

Hydrofluoric acid

20.0

1.18

49.0

28.9

34.5

Nitric acid

63.01

1.42

70.4

15.9

63.0

Perchloric acid

100.47

1.67

70.5

11.7

85.5

Phosphoric acid

97.10

1.70

85.5

14.8

67.5

Pyridine

79.10

0.982

100

12.4

80.6

Potassium hydroxide (soln)

56.11

1.46

45

11.7

85.5

Sodium hydroxide (soln)

40.00

1.54

50.5

19.4

51.5

Sulfuric acid

98.08

1.84

96.0

18.0

55.8

Triethanolamine

149.19

1.124

100

7.53

132.7

11.108

SECTION

11

TABLE 11.48

Standard Stock Solutions (

Continued

)

Element

Procedure

Gold

Dissolve 1.000 g Au in 10 ml of hot HNO

3 by dropwise addition of HCl, boil to expel

oxides of nitrogen and chlorine, and dilute to volume. Store in amber container away

from light.

Hafnium

Transfer 1.000 g Hf to Pt dish, add 10 ml of 9

M

H 2 SO

4 , and then slowly add HF drop-

wise until dissolution is complete. Dilute to volume with 10% H

2 SO

4 .

Holmium

Dissolve 1.1455 g Ho

2 O

3 in 50 ml of 2

M HCl; dilute to volume.

Indium

Dissolve 1.000 g In in 50 ml of 2

M HCl; dilute to volume.

Iodine

Dissolve 1.308 g Kl in water and dilute to volume.

Iridium

(1) Dissolve 2.465 g Na

3 IrCl

6 in water and dilute to volume. (2) Transfer 1.000 g Ir

sponge to a glass tube, add 20 ml of HCl and 1 ml of HClO

4 . Seal the tube and place

in an oven at 300 C for 24 hr. Cool, break open the tube, transfer the solution to a

volumetric flask, and dilute to volume. Observe all safety precautions in opening the

glass tube.

Iron

Dissolve 1.000 g Fe wire in 20 ml of 5

M

HCl; dilute to volume.

Lanthanum

Dissolve 1.1717 g La

2 O

3

(dried at 110

C) in 50 ml of 5

M HCl, and dilute to volume.

Lead

(1) Dissolve 1.5985 g Pb(NO

3 )2

in water plus 10 ml HNO

3 , and dilute to volume. (2)

Dissolve 1.000 g Pb in 10 ml HNO

3 , and dilute to volume.

Lithium

Dissolve a slurry of 5.3228 g Li

2 CO

3

in 300 ml of water by addition of 15 ml HCl; after

release of CO

2

by swirling, dilute to volume.

Lutetium

Dissolve 1.6079 g LuCl

3

in water and dilute to volume.

Magnesium

Dissolve 1.000 g Mg in 50 ml of 1

M

HCl and dilute to volume.

Manganese

(1) Dissolve 1.000 g Mn in 10 ml HCl plus 1 ml HNO

3 , and dilute to volume. (2) Dis-

solve 3.0764 g MnSO

4 · H

2 O (dried at 105

C for 4 hr) in water and dilute to volume.

(3) Dissolve 1.5824 g MnO

2

in 10 HCl in a good hood, evaporate to gentle dryness,

dissolve residue in water and dilute to volume.

Mercury

Dissolve 1.000 g Hg in 10 ml of 5

M

HNO

3 and dilute to volume.

Molybdenum

(1) Dissolve 2.0425 g (NH

4 )2 MoO

4

in water and dilute to volume. (2) Dissolve 1.5003 g

MoO

3

in 100 ml of 2

M ammonia, and dilute to volume.

Neodymium

Dissolve 1.7373 g NdCl

3 in 100 ml 1

M HCl and dilute to volume.

Nickel

Dissolve 1.000 g Ni in 10 ml hot HNO

3 , cool, and dilute to volume.

Niobium

Transfer 1.000 g Nb (or 1.4305 g Nb

2 O

5) to Pt dish, add 20 ml HF, and heat gently to

complete dissolution. Cool, add 40 ml H

2 SO 4

, and evaporate to fumes of SO

3 . Cool

and dilute to volume with 8

M

H

2 SO

4 .

Osmium

Dissolve 1.3360 g OsO

4

in water and dilute to 100 ml. Prepare only as needed as solu-

tion loses strength on standing unless Os is reduced by SO

2 and water is replaced by

100 ml 0.M1

HCl.

Palladium

Dissolve 1.000 g Pd in 10 ml of HNO

3

by dropwise addition of HCl to hot solution;

dilute to volume.

Phosphorus

Dissolve 4.260 g (NH

4 )2 HPO

4 in water and dilute to volume.

Platinum

Dissolve 1.000 g Pt in 40 ml of hot aqua regia, evaporate to incipient dryness, add 10

ml HCl and again evaporate to moist residue. Add 10 ml HCl and dilute to volume.

Potassium

Dissolve 1.9067 g KCl (or 2.8415 g KNO

3 ) in water and dilute to volume.

Praseodymium

Dissolve 1.1703 g Pr

2 O

3

in 50 ml of 2

M

HCl; dilute to volume.

Rhenium

Dissolve 1.000 g Re in 10 ml of 8

M

HNO

3 in an ice bath until initial reaction subsides,

then dilute to volume.

Rhodium

Dissolve 1.000 g Rh by the sealed-tube method described under iridium.

Rubidium

Dissolve 1.4148 g RbCl in water. Standardize as described under cesium. Rb (in

g/ml)

(40)(0.320)(wt of residue).

Ruthenium

Dissolve 1.317 g RuO

2

in 15 ml of HCl; dilute to volume.

Samarium

Dissolve 1.1596 g Sm

2 O

3 in 50 ml of 2

M

HCl; dilute to volume.

Scandium

Dissolve 1.5338 g Sc

2 O

3

in 50 ml of 2

M

HCl; dilute to volume.