Preparation • Over 300 recipes of common

"Your Safer Source for Science Supplies"

Laboratory Solution Preparation

Laboratory Solution Preparation

? Basic concepts of preparing solutions

? Over 300 recipes of common laboratory solutions

? Solution preparation tips

Many of the reagents used in science are in the form of solutions which need to be purchased or prepared. For many purposes, the exact value of concentration is not critical; in other cases, the concentration of the solution and its method of preparation must be as accurate as possible. The Flinn Laboratory Solution Preparation reference section is designed for both the novice and experienced solution maker. It provides valuable information on the basic concepts of preparing solu tions and instructions for preparing most solutions required in the high school science laboratory. Professional quality solutions are possible when high quality and fresh chemicals and solvents are used, and meticulous procedures are followed. Many of the solutions described

in this section are available ready-made from Flinn Scientific to save valuable laboratory prep time. The section is divided into several parts for your convenience. Basic concepts of preparing solutions Preparation of simple inorganic salt solutions Preparations of acid and base solutions Recipes for Biological, Histological, and Chemical solutions

Basic Concepts of Preparing Solutions

Molarity

The most common unit of solution concentration is molarity (M). The molarity of a solution is defined as the number of moles of solute per one liter of solution. Note that the unit of volume for molarity is liters, not milliliters or some other unit. Also note that one liter of solution contains both the solute and the solvent. Molarity, therefore, is a ratio between moles of solute and liters of solution. To prepare laboratory solutions, usually a given volume and molarity are required. To determine molarity, the formula weight or molar mass of the solute is needed. The following exam ples illustrate the calculations for preparing solutions.

If starting with a solid, use the following procedure:

? Determine the mass in grams of one mole of solute, the molar mass, MMs.

? Decide volume of solution required, in liters, V.

? Decide molarity of solution required, M.

? Calculate grams of solute (gs) required using equation 1. eq. 1. gs = MMs x M x V

? Example: Prepare 800 mL of 2 M sodium chloride. (MMNaCl = 58.45 g/mol)

gNaCl = 58.45 g/mol x 2 mol/L x 0.8 L gNaCl = 93.52 g NaCl

Dissolve 93.52 g of NaCl in about 400 mL of distilled water, then add more water until final volume is 800 mL.

If starting with a solution or liquid reagent:

? When diluting more concentrated solutions, decide what volume (V2) and molarity (M2) the final solution should be. Volume can be expressed in liters or milliliters.

? Determine molarity (M1) of starting, more concentrated solu tion.

? Calculate volume of starting solution (V1) required using equa tion 2. Note: V1 must be in the same units as V2. eq. 2. M1V1 = M2V2

? Example: Prepare 100 mL of 1.0 M hydrochloric acid from concentrated (12.1 M) hydrochloric acid. M1V1 = M2V2 (12.1 M)(V1) = (1.0 M)(100 mL) V1 = 8.26 mL conc. HCl

Add 8.26 mL of concentrated HCl to about 50 mL of distilled water, stir, then add water up to 100 mL.

Percent Solutions

Mass percent solutions are defined based on the grams of solute per 100 grams of solution.

Example: 2 0 g of sodium chloride in 100 g of solution is a 20% by mass solution.

Volume percent solutions are defined as milliliters of solute per 100 mL of solution.

Example: 1 0 mL of ethyl alcohol plus 90 mL of H2O (making approx. 100 mL of solution) is a 10% by volume solution.

Mass-volume percent solutions are also very common. These solutions are indicated by w/v% and are defined as the grams of solute per 100 milliliters of solution.

Example: 1 g of phenolphthalein in 100 mL of 95% ethyl alcohol is a 1 w/v% solution.

BASIC CONCEPTS OF PREPARING SOLUTIONS continued on next page. ? 2011 Flinn Scientific, Inc. All Rights Reserved.

Safety Reference

Basic Concepts of Preparing Solutions, continued

1-800-452-1261



Conversion Between Percent Solutions

You may wish to convert mass percent to volume percent or vice versa. If so, follow this procedure:

A 10% by mass solution of ethyl alcohol in water contains 10 g of ethyl alcohol and 90 g of water. 1. The formula for determining the volume of the component (ethyl alcohol in our example) is: mass of ethyl alcohol Volume = -------------------- density of ethyl alcohol 2. Determine the volume of the total solution by dividing the mass of the solution by the density of the solution. 3. Determine the percent by volume by dividing the volume of the component by the volume of the solution. Let's solve 1, 2, and 3 above as follows: 1. Mass of ethyl alcohol = 10 g (given) Density of ethyl alcohol = 0.794 g/mL (from handbook) mass Volume = ------ density Volume of ethyl alcohol = ----1--0 g---- = 12.6 mL

0.794 g/mL 2. Mass of solution = 100 g (given)

Density of solution (10% ethyl alcohol) = 0 .983 g/mL (from handbook)

100 g Volume of solution = ---------- = 101.8 mL*

0.983 g/mL 3. Volume percent of solution

volume of ethyl alcohol 12.6 Percent = -------------------- = ------ = 12.4%

total volume of solution 101.8 Reverse the procedure to convert volume percent to mass percent.

* The volume percent statement generally is accurate but the volume percent is not always calculated directly from the volumes of the mixed ingredients because the final volume may not equal the sum of the separate volumes. In our solution (No. 2 above) note that if the alcohol volume (12.6 mL) is added to the water volume (90 mL), the final volume is less than 102.6 mL.

? 2011 Flinn Scientific, Inc. All Rights Reserved.

Calculating Molarity from Percent Solutions

To determine the molarity of a mass percent solution, the density of the solution is required. Use the following proce dure:

1. Determine the mass of solution by multiplying the volume of the solution by the density of the solution.

mass = volume x density

2. Determine concentration in percent by mass of the solute in solution. Change to the decimal equivalent.

3. Calculate the molar mass of the compound, MM.

4. Multiply mass (step 1) by mass % (step 2) and divide by molecular mass (step 3) to find the number of moles present in the whole solution.

5. Divide the number of moles (step 4) by the volume in liters of the solution to find the molarity of the solution.

Example: D etermine molarity of 37.2% hydrochloric acid (density 1.19 g/mL).

1. Mass of solution = 1,000 mL x 1.19 g/mL = 1,190 g

2. Mass % = 37.2 % = 0.372

3. Molar mass of hydrochloric acid = 36.4 g/mol

4. mass x mass % 1,190 g x 0.372 ---------------- = ---------------- = 12.1 moles MMHCl 36.4 g/mol

5. Molarity = moles/liters = 12.1 moles/1 liter = 12.1 M

Definitions

Buffer: A solution which tends to maintain a constant pH when excess acid or base is added.

Concentrated: For some commonly used acids and bases, the maximum solubility (at room temperature) in an aqueous solution or as a pure liquid.

Concentration: The relative amount of solute and solvent in a solution.

Hydrates: Compounds containing water chemically combined in a definite ratio. Computations using formula weight must take the water molecules into account.

Miscible: The ability of two liquids to be completely soluble in one another.

Molality: A concentration unit (m); defined as the number of moles of solute divided by the number of kilograms of solvent.

Molar Mass: The mass of a mole of any element or compound.

Molarity: A concentration unit (M); defined as the number of moles of solute divided by liters of solution.

"Your Safer Source for Science Supplies"

Preparation of Simple Inorganic Salt Solutions

Preparation of Simple Inorganic Salt Solutions

Name / Formula / F.W.

Aluminum chloride AlCl3 ? 6H2O 241.43

Aluminum nitrate Al(NO3)3 ? 9H2O 375.13

Aluminum sulfate Al2(SO4)3 ? 18H2O 666.42

Ammonium acetate NH4C2H3O2 77.08

Ammonium chloride NH4Cl 53.49

Ammonium nitrate NH4NO3 80.04

Ammonium sulfate (NH4)2SO4 132.1

Barium chloride BaCl2 ? 2H2O 244.28

Barium hydroxide Ba(OH)2 ? 8H2O 315.50

Barium nitrate Ba(NO3)2 261.35

Bismuth nitrate Bi(NO3)3 ? 5H2O 485.1

Concentration

0.2 M 0.05 M

0.1 M

g/L

48.3 g 12.1 g

37.5 g

0.1 M

66.6 g

1.0 M 0.1 M

1.0 M 0.5 M

1.0 M 0.5 M 0.1 M 0.1 M

77.1 g 7.7 g

53.5 g 26.7 g

80.0 g 40.0 g 8.0 g 13.2 g

0.1 M

24.4 g

0.1 M

31.5 g

0.5 M 0.1 M

0.1 M

130.7 g 26.1 g

48.5 g in 500 mL 6M

HNO3*

Normality: A concentration unit (N); defined as the number of equivalents of solute per liter of solution. (e.g., 1 M H2SO4 = 2 N H2SO4)

Saturated Solution: A solution that contains the maxim um amount of a particular solute that will dissolve at that temperature.

Solute: The substance which is dissolved, or has gone into solution (typically a solid).

Solution: A uniform homogeneous mixture of two or more substances. The individual substances may be present in varying amounts.

Solvent: The substance which does the dissolving (typically a liquid, such as water or alcohol). Must be greater than 50% of the solution.

Standard Solution: A very precise solution, usually to 3?4 significant figures, used in quantitative analysis or an analytical procedure.

Supersaturated Solution: A solution that contains more solute than equilibrium conditions allow; it is unstable and the solute may precipitate upon slight agitation or addition of a single crystal.

Name / Formula / F.W.

Bismuth trichloride BiCl3 315.34

Concentration

0.2 M

g/L

63.1 g in 500 mL 3M

HCl*

Cadmium chloride CdCl2 ? 21/2H2O 228.34

0.1 M

22.8 g

Cadmium nitrate Cd(NO3)2 ? 4H2O 308.49

0.1 M

30.8 g

Calcium acetate Ca(C2H3O2)2 ? H2O 176.19

0.5 M 0.1 M

88.1 g 17.6 g

Calcium chloride CaCl2 ? 2H2O 147.02

1.0 M 0.1 M

147.0 g 14.7 g

Calcium hydroxide

saturated

2 g

Ca(OH)2

74.10

Calcium nitrate Ca(NO3)2 ? 4H2O 236.16

0.5 M 0.1 M

118.1 g 23.6 g

Chromium(III) chloride CrCl3 ? 6H2O 266.48

0.1 M

26.6 g

Chromium(III) nitrate Cr(NO3)3 ? 9H2O 400.18

0.1 M

40.0 g

Cobalt(II) chloride CoCl2 ? 6H2O 237.95

0.1 M

23.8 g

Cobalt(II) nitrate Co(NO3)2 ? 6H2O 291.05

0.1M

29.1 g

Copper(II) chloride CuCl2 ? 2H2O 170.49

0.5 M 0.1 M

85.2 g 17.0 g

Copper(II) nitrate Cu(NO3)2 ? 3H2O 241.6

0.5 M 0.1 M

120.8 g 24.2 g

Copper(II) sulfate CuSO4 ? 5H2O 249.69

1.0 M 0.5 M

249.7 g 124.8 g

Iron(II) sulfate FeSO4 ? 7H2O 278.03

0.01 M

2.8 g and 1 mL conc.

H2SO4*

Iron(III) chloride FeCl3 ? 6H2O 270.32

1.0 M 0.1 M

270.3 g 27.0 g

Iron(III) nitrate Fe(NO3)3 ? 9H2O 404.00

0.1 M

40.4 g

* Add solid to acid solution, stir, then add to water. Dilute to 1 L. Remember, always add acid to water.

Approximate amount for 1 L of saturated solution. Keep adding solute until it no longer dissolves; stir for 1 hour, then filter.

PREPARATION OF SIMPLE INORGANIC SALT SOLUTIONS continued on next page.

? 2011 Flinn Scientific, Inc. All Rights Reserved.

Safety Reference

Preparation of Simple Inorganic Salt Solutions, continued

1-800-452-1261



Name / Formula / F.W.

Lead acetate Pb(C2H3O2)2 ? 3H2O 379.34

Lead chloride PbCl2 278.12

Lead nitrate Pb(NO3)2 331.2

Lithium carbonate Li2CO3 73.89

Lithium chloride LiCl 42.40

Lithium nitrate LiNO3 68.95

Magnesium bromide MgBr2 ? 6H2O 292.25

Magnesium chloride MgCl2 ? 6H2O 203.33

Magnesium hydroxide Mg(OH)2 58.34

Magnesium nitrate Mg(NO3)2 ? 6H2O 256.43

Magnesium sulfate MgSO4 ? 7H2O 246.50

Manganese chloride MnCl2 ? 4H2O 197.91

Concentration

0.1M

saturated

1 M 0.5 M 0.1 M 0.1 M

1.0 M 0.1 M

1.0 M 0.5 M

0.1 M

1.0 M 0.1 M

saturated

0.1 M

0.5 M 0.1 M

0.5 M 0.1 M

g/L

38.0 g

12.0 g

331.2 g? 165.6 g 33.1 g

7.4 g

42.4 g 4.2 g

69.0 g 34.5 g

29.2 g

203.3 g 20.3 g 300 g

25.6 g

123.3 g 24.7 g

99.0 g 19.8 g

Make a Solution

Name / Formula / F.W.

Concentration

g/L

Manganese sulfate MnSO4 ? H2O 169.01

Mercury(II) chloride HgCl2 271.50

Mercury(II) nitrate Hg(NO3)2 ? H2O 342.63

Mercury(I) nitrate Hg2(NO3)2 ? 2H2O 561.22

Mercury(I) sulfate Hg2SO4 497.24

Nickel chloride NiCl2 ? 6H2O 237.72

Nickel nitrate Ni(NO3)2 ? 6H2O 290.82

Nickel sulfate NiSO4 ? 6H2O 262.87

Potassium bromide KBr 119.02

Potassium carbonate K2CO3 138.21

Potassium chloride KCl 74.56

0.2 M 0.1 M

0.25 M 0.10 M

0.1 M

0.1 M

0.1 M

0.25 M 0.1 M

1 M 0.2 M

1.0 M 0.5 M

0.5 M 0.1 M

0.5 M 0.1 M

0.5 M 0.1 M

33.8 g 16.9 g

67.9 g 27.2 g

34.2 g in 50 mL conc.

HNO3* 56.2 g in 100 mL conc. HNO3* 49.7 g in 30 mL 1 M HNO3*

59.4 g 23.8 g

290.8 g 58.2 g

262.9 g 131.4 g

59.5 g 11.9 g

69.1 g 13.8 g

37.3 g 7.5 g

* Add solid to acid solution, stir, then add to water. Dilute to 1 L. Remember, always add acid to water.

Approximate amount for 1 L of saturated solution. Keep adding solute until it no longer dissolves; stir for 1 hour, then filter.

? Use 7.5 mL conc. HNO3 to help dissolve.

PREPARATION OF SIMPLE INORGANIC SALT SOLUTIONS continued on next page.

1. Weigh solid.

2. Fill volumet ric flask 1/3?1/2 full with deionized or distilled water.

3. Transfer solid, wash out weigh ing dish.

4. Stir until dissolved. Add more water if necessary.

5. Add deionized or distilled water up to mark.

? 2011 Flinn Scientific, Inc. All Rights Reserved.

"Your Safer Source for Science Supplies"

Preparation of Simple Inorganic Salt Solutions

Preparation of Simple Inorganic Salt Solutions, continued

Name / Formula / F.W.

Concentration

Potassium chromate K2CrO4 194.21

1.0 M 0.5 M 0.1 M

Potassium dichromate K2Cr2O7 294.22

0.1 M

Potassium ferricyanide K3Fe(CN)6 329.26

0.5 M 0.1 M

Potassium ferrocyanide K4Fe(CN)6 ? 3H2O 422.41

0.1 M

Potassium hydrogen phthalate KHC8H4O4 204.23

0.1 M

Potassium hydroxide see page 118

Potassium iodate KIO3 214.01

saturated 0.2 M 0.1 M

Potassium iodide Kl 166.01

1 M 0.5 M 0.2 M

Potassium nitrate KNO3 101.11

0.5 M 0.1 M

Potassium permanganate KMnO4 158.04

0.2 M 0.1 M 0.01 M

Potassium phosphate, monobasic KH2PO4 136.09

0.1 M

Potassium phosphate, dibasic K2HPO4 174.18

0.1 M

g/L

194.2 g 97.1 g 19.4 g 29.4 g

164.6 g 32.9 g

42.2 g

20.4 g

214.0 g 42.8 g 21.4 g

166.0 g 83.0 g 33.2 g 50.6 g 10.1 g

31.6 g 15.8 g 1.6 g 13.6 g

17.4 g

Name / Formula / F.W.

Potassium phosphate, tribasic K3PO4 212.27

Potassium sulfate K2SO4 174.27

Potassium thiocyanate KSCN 97.18

Silver nitrate AgNO3 169.87

Sodium acetate NaC2H3O2 ? 3H2O 136.08

Sodium bicarbonate NaHCO3 84.01

Sodium borate Na2B4O7 ? 10H2O 381.42

Sodium bromide NaBr 102.90

Sodium carbonate Na2CO3 105.99

Sodium carbonate Na2CO3 ? H2O 124.00

Concentration

0.1 M

0.5 M 0.1 M

1.0 M 0.5 M 0.1 M 0.5 M 0.1 M

1 M 0.5 M

0.5 M 0.1 M

4 %

1.0 M 0.1 M

saturated 1.0 M 0.1 M 1.0 M 0.1 M

g/L

21.2 g

87.1 g 17.4 g

97.2 g 48.6 g 9.7 g 84.9 g 17.0 g

136.1 g 68.0 g

42.0 g 8.4 g

40.0 g

102.9 g 10.3 g

214.0 g 106.0 g 10.6 g 124.0 g 12.4 g

* Add solid to acid solution, stir, then add to water. Dilute to 1 L. Remember, always add acid to water.

Approximate amount for 1 L of saturated solution. Keep adding solute until it no longer dissolves; stir for 1 hour, then filter.

PREPARATION OF SIMPLE INORGANIC SALT SOLUTIONS continued on next page.

General Solubility Rules for Inorganic Compounds

Nitrates (NO3?): All nitrates are soluble.

Acetates (C2H3O2?): All acetates are soluble; silver acetate is moderately soluble.

Bromides (Br?) Chlorides (Cl?) and Iodides (I?): Most are soluble except for salts containing silver, lead, and mercury.

Sulfates (SO42?): All sulfates are soluble except barium and lead. Silver, mercury(I), and calcium are slightly soluble.

Hydrogen sulfates (HSO4?) : The hydrogen sulfates (aka bisul fates) are more soluble than the sulfates.

Carbonates (CO32?), phosphates (PO43?), chromates (CrO42?), silicates (SiO42?): All carbonates, phosphates, chromates, and silicates are insoluble, except those of sodium, potassium, and ammonium. An exception is MgCrO4, which is soluble.

Hydroxides (OH?): All hydroxides (except lithium, sodium, potas sium, cesium, rubidium, and ammonium) are insoluble; Ba(OH)2, Ca(OH)2 and Sr(OH)2 are slightly soluble.

Sulfides (S2?): All sulfides (except sodium, potassium, ammonium, magnesium, calcium and barium) are insoluble. Aluminum and chromium sulfides are hydrolyzed and precipitate as hydroxides.

Sodium (Na+), potassium (K+), ammonium (NH4+): All sodium, potassium, and ammonium salts are soluble. (Except some transi tion metal compounds.)

Silver (Ag+): All silver salts are insoluble. Exceptions: AgNO3 and AgClO4; AgC2H3O2 and Ag2SO4 are moderately soluble.

? 2011 Flinn Scientific, Inc. All Rights Reserved.

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download