flinnsci.com CHEMICALS SAVE ON HAZMAT FEES 37
HAZARD ALERT: Buffers in low pH range are strongly acidic; those in
high pH range are strongly alkaline.
Storage: Best and most conveniently stored together with proper recognition
and precaution for their individual acid or alkaline nature. Keep bottles
tightly closed.
Disposal: #26b
Shelf Life: Ready-to-use Buffer Solutions’ shelf life varies depending on pH
value—from good to poor. The higher the pH value, the shorter the shelf life.
Storage conditions vary so widely that it isn’t possible to be specific about
shelf life. Concentrated buffers, buffer capsules and buffers in Chemvelopes®
all have better long-term shelf life than standard buffers.
Technical Note: The pH 4, 7 and 10 buffer solutions are dyed for convenience
to allow easy identification and prevent con fusion. These three buffers
are the standards used to calibrate pH meters.
Bromphenol Blue Indicator Solution
0.04%, aqueous
B0065 100 mL $6.60
Storage: Organic #9
Disposal: #26b
Shelf Life: Indefinite
Color and Odor: Dark purple, odorless liquid.
Bromthymol Blue
indicator, sodium salt
pH 6.0 yellow to 7.6 blue
powder
C27H27Br2O5SNa
F.W. 646.38
Reagent B0046 5 g $22.68
Laboratory grade B0233 5 g 12.85
Storage: Organic #9
Disposal: #26a
Shelf Life: Indefinite
Soluble: Water
Color and Odor: Blue-green, odorless solid.
CAS No. 34722-90-2
Bromthymol Blue Indicator Solution
0.04%, aqueous B0173 100 mL $ 3.65
B0047 500 mL 7.52
B0228 1000 mL 11.02
Storage: Organic #9
Disposal: #26b
Shelf Life: Indefinite
Color and Odor: Blue-green, odorless liquid.
Buffer Solutions
concentrated
pH accuracy ±0.02 at 25 °C.
pH 4.00 when 1 volume is diluted to 5 volumes
B0098 500 mL $14.03
pH 7.00 when 1 volume is diluted to 25 volumes
B0099 500 mL 19.78
pH 10.00 when 1 volume is diluted to 10 volumes
B0100 500 mL 14.40
HAZARD ALERT: Low and high pH concentrates (pH 4 and 10) should be
treated as strongly acidic and alkaline solutions, respectively.
Storage: With Inorganic #2 family for convenience.
Disposal: #26b
Shelf Life: Much better than prepared buffers that are ready to use.
Concentrates last longer and take up less shelf space.
Buffer Solutions
pH accuracy ±0.02 at 25 °C
500 mL bottle
Catalog No. pH Value Price
B0087 2.00 $15.75
B0088 3.00 15.18
B0089 4.00 (red) 7.03
B0090 5.00 15.80
B0091 6.00 15.75
B0092 7.00 (green) 6.99
B0093 8.00 15.86
B0094 9.00 15.29
B0095 10.00 (blue) 7.20
B0096 11.00 15.80
B0097 12.00 15.69
Buffer Solutions continued
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Understand Buffer Solutions
and pH
What is pH?
The pH scale represents the acidity or alkalinity of an aqueous solution. pH is
defined as the negative logarithm of the hydrogen ion concentration of a solution.
pH = –logH+.
Absolutely pure water is the standard used in determining pH value. Since pH
measurements depend on the chemical properties of water, the pH scale is not
accurate for nonaqueous solutions. The pH scale was established with a range of 0
to 14 pH units. The low end of the scale is acid, the high end alkaline, with pH 7.00 at
the mid-point as neutral.
Each unit on the pH scale represents a tenfold difference in acidity level. For
example, pH 4 is ten times as acidic as pH 5. A pH 3 solution has ten times the acidity
level of a pH 4 solution and 100 times the acidity level of a pH 5 solution.
What is a buffer?
A buffer is a chemical substance that resists changes in pH upon the addition of
excess strong acid or strong base.
A buffer solution contains both a weak acid and its conjugate weak base. The weak
acid component neutralizes any excess strong base added to the solution while the
weak base component neutralizes any excess strong acid that may be added. As a
result, a buffer solution maintains a constant hydrogen ion concentration despite the
addition of relatively large quantities of acid or base.
Science teachers should know that water (distilled or deionized) has no “buffer
effect.” In fact, the use of “dip and read” test papers will quickly influence the pH of the
pure water. Almost always, the test paper used in such water will read pH 5.00 after
the paper has been dipped in the water even though the actual pH of the water may
be entirely different. In this example, the test paper itself has had an effect on the pH
value of the water. Good quality water is not a substitute for a buffer.
What are pH test papers?
pH papers are made with special indicator dyes that react (change color) at specific
pH values. Two pH units is the use ful limit for most indicators and indicator papers.
No further perceptible color change will occur regardless of a further pH change in
the solution being tested. For example, using a test paper with a pH range of 6.00 to
8.00, a reading can be successfully taken if the pH falls between the aforementioned
points. If the pH is actually below 6.00 or higher than 8.00, the test paper cannot
detect that change and will simply change color to one extreme or the other of its
2.00 pH unit range.
pH papers may not be reliable in aqueous solutions containing proteins or alkaloids
(e.g., nitrogen-based substances of plant origin like nicotine).
Continued on next column.
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