Ppt on acid-base indicators colors

Three important elements in Winemaking

The amount of titrate solution used is the key to titratable acidity (TA) of the wine. Each cc of solution represents 0.1% TA. Thus, if 5-1/2 cc of solution were used to produce the indicated color change, the TA of the wine or must equals 0.55/safest method, ensuring the wine does not suffer from oxidation or further processing. SO2 is often removed from wine by aerating. This is based on the slow oxidation of the SO2 and is only really suitable for slightly excessive doses of SO2. Free SO2 can be removed /


Chapter Fifteen 1 Hall © 2005 Prentice Hall © 2005 General Chemistry 4 th edition, Hill, Petrucci, McCreary, Perry Acids, Bases, and AcidBase Equilibria.

? Chapter Fifteen 60 Hall © 2005 Prentice Hall © 2005 General Chemistry 4 th edition, Hill, Petrucci, McCreary, Perry AcidBase Indicators An acidbase indicator is a weak acid or base. The acid form (HA) of the indicator has one color, the conjugate base (A – ) has a different color. One of the “colors” may be colorless. In an acidic solution, [H 3 O + ] is high. Because H 3 O + is a common ion, it suppresses the/


Topic 1C – Part II Acid Base Equilibria and Ksp

using titration curve plots. We use an indicator, a chemical that changes colors at various pH’s. Most acid-base titrations involve the addition of one colorless /acid at equivalence point find pH with ICE and Kb ** Weak base after equivalence - leftover strong base. Indicators Weak acids that change color when they become bases. weak acid written HIn Weak base HIn H+ + In- clear red Equilibrium is controlled by pH End point - when the indicator changes color. Indicators Since it is an equilibrium the color/


Titrations Main Idea: Titrations are an application of acid-base neutralization reactions that require the use of an indicator. 1.

point for the titration of HPr (a weak acid) with NaOH (a strong base) lies at pH 8.80. 10 Acid-Base Indicators Chemists often use a chemical dye rather than a pH meter to detect the equivalence point of an acid-base titration. Chemical dyes whose colors are affected by acidic and basic solutions are called acid-base indicators. Many natural substances act as indicators. – If you use lemon juice in your/


Acid-Base Equilibria.

is a small system. Acid-Base Indicators An acid-base indicator is a weak acid having one color and the conjugate base of the acid having a different color. One of the “colors” may be colorless. HIn + H2O º H3O+ + In- color 1 color 2 Acid-base indicators are often used for applications in which a precise pH reading isn’t necessary. A common indicator used in introductory chemistry laboratories is litmus. 17-3 Acid-Base Indicators Color of some substances depends on/


Acids and Bases Vanderbilt Student Volunteers for Science Training Presentation Spring 2014.

be useful at different pH’s. For example: Litmus can tell us if something is either a base or an acid Methyl orange indicator changes color at ph3/4. It is red below pH 4 and yellow above pH 4. Universal indicator has a large number of color changes at different pH’s and can more precisely tell us what the pH of a solution is/


Acids and Bases Strength of Acids and Bases. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Lemon juice, which contains.

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. An indicator (HIn) is an acid or a base that dissociates in a known pH range. Indicators work because their acid form and base form have different colors in solution. Measuring pH Acid-Base Indicators The acid form of the indicator (HIn) is dominant at low pH and high [H + ]. The base form (In − ) is dominant at high pH and high [OH − ]. Copyright/


Introduction to Acids, Bases and Salts. Arrhenius Definition of Acids and Bases Acids produce H + in aqueous (water) solutions Acids produce H + in aqueous.

meter Use an electronic pH meter Use an indicator such as litmus Use an indicator such as litmus Use pH paper containing universal indicator Use pH paper containing universal indicator Acid/Bases Indicators See Table M Examples: Litmus Litmus pH range for color change (4.5 – 8.3) pH range for color change (4.5 – 8.3) Color change: red to blue Color change: red to blue Phenolphthalein Phenolphthalein pH range/


Acids and Bases Agenda “ the acid test ”“ acid drop ”“ acid rain ” “ put the acid on ”“ do acid ”“ acid head ” Day 71 – Strong and Weak Acids and Bases.

given for a certain temperature (25 o C), thus may change at different temperatures – what if the solution already has a color, like paint? – the ability of the human eye to distinguish colors is limited Acid-Base Indicators A pH meter may give more definitive results – some are large, others portable – works by measuring the voltage between two electrodes; typically accurate to within 0.01/


Acid-Base Theories n OBJECTIVES: –Compare and contrast acids and bases as defined by the theories of: a) Arrhenius, b) Brønsted-Lowry, and c) Lewis.

given for a certain temperature (25 o C), thus may change at different temperatures –what if the solution already has a color, like paint? – the ability of the human eye to distinguish colors is limited Acid-Base Indicators n A pH meter may give more definitive results –some are large, others portable –works by measuring the voltage between two electrodes; typically accurate to within 0/


19.2 Hydrogen Ions and Acidity > 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Chapter 19 Acids, Bases, and Salts 19.1.

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. An indicator (HIn) is an acid or a base that dissociates in a known pH range. Indicators work because their acid form and base form have different colors in solution. Measuring pH Acid-Base Indicators The acid form of the indicator (HIn) is dominant at low pH and high [H + ]. The base form (In − ) is dominant at high pH and high [OH − ]. 19/


Chapter 19 “Acids, Bases, and Salts”. Properties of Acids n They taste sour (don’t try this at home). n They can conduct electricity. –Can be strong or.

given for a certain temperature (25 o C), thus may change at different temperatures –what if the solution already has a color, like paint? – the ability of the human eye to distinguish colors is limited Acid-Base Indicators n A pH meter may give more definitive results –some are large, others portable –works by measuring the voltage between two electrodes; typically accurate to within 0/


Chapt. 18 – Acids and Bases 18.1Acids and Bases: An Introduction 18.2 Strengths of Acids and Bases 18.3Hydrogen Ions and pH 18.4 Neutralization.

hydrolysis (topic discussed later) Must choose pH indicator end point accordingly Matching of equivalence point and pH indicator end point – titration of strong acid with strong base Matching of equivalence point and pH indicator end point – titration of weak acid with strong base Acid Base Indicators are weak acids or bases themselves Hin (aq) + H 2 O (l)  H 3 O + (aq) + In - (aq) Color A Color B Acid Base Indicators K a = [H 3 O + ] [In/


Acids/Bases/Salts Properties. Common Acids Lacticsour milk Aceticvinegar Phosphorictart taste in soda Citriccitrus fruits Malicapples Tartaricgrapes Formicant.

so that we can see what is happening over time. Some indicators change color more than once and can be added to solutions so that we can see what is happening over time. Acid/Bases/Salts Neutralization/Titrations Neutralization  Chemical reaction between an acid and a base.  Products are a salt (ionic compound) and water. Neutralization ACID + BASE  SALT + WATER HCl + NaOH  NaCl + H 2 O HC 2/


Chapter 19 “Acids, Bases, and Salts” Pre-AP Chemistry Charles Page High School Stephen L. Cotton.

given for a certain temperature (25 o C), thus may change at different temperatures –what if the solution already has a color, like paint? – the ability of the human eye to distinguish colors is limited Acid-Base Indicators n A pH meter may give more definitive results –some are large, others portable –works by measuring the voltage between two electrodes; typically accurate to within 0/


Chapter 19 “Acids, Bases, and Salts” Pequannock Township High School Chemistry Mrs. Munoz.

given for a certain temperature (25 o C); thus may change at different temperatures.  What if the solution already has a color, like paint?  The ability of the human eye to distinguish colors is limited. Acid-Base Indicators A pH meter may give more definitive results. Some are large, others portable. Works by measuring the voltage between two electrodes; typically accurate to within 0.01/


Chapter 19 Acids & Bases Section 19.1 AcidBase Theories 1.

+ ] pH = - log (2.5 x 10 - 4 ) pH = 3.60 44 AcidBase Indicators Indicator Indicator - is an acid or a base that undergoes dissociation in a known pH range An indicator is a valuable tool for measuring pH because its acid form and base form have different color in solution. For each indicator, the change from dominating acid form to dominating base form occurs in a narrow range of approximately two pH units/


Acids and Bases RNA uses amino-acids to build proteins/enzymes It is the acids in citrus fruits that give them the sour taste and allows the fruit to stay.

neutralize to form a polypeptide 10 Indicators  chemicals which change color depending on the acidity/basicity  many vegetable dyes are indicators  anthocyanins  litmus  from Spanish moss  red in acid, blue in base  phenolphthalein  found in laxatives  red in base, colorless in acid  chemicals which change color depending on the acidity/basicity  many vegetable dyes are indicators  anthocyanins  litmus  from Spanish moss  red in acid, blue in base  phenolphthalein  found in laxatives  red/


 OBJECTIVES: Define the properties of acids and bases.

by the loss or gain of a single hydrogen ion.  Chemical Indicators? They are weak acids or bases that have a different color from their original acid and base  General equation is: HA (aq) + H 2 O (l) ↔ H 3 O + (aq) + A - (aq)  Acid + Base ↔ Conjugate acid + Conjugate base  NH 3 + H 2 O ↔ NH 4 1+ + OH 1- base acid c.a. c.b.  HCl + H 2 O ↔ H 3/


Acids & Bases. Properties of Acids Sour taste Change color of acid-base indicators (red in pH paper) Some react with active metals to produce hydrogen.

(aq) Na 2 SO 4 (aq) + 2H 2 O (l) Some are electrolytes Examples of Acids Lemons and oranges - citric acid Vinegar - 5% by mass acetic acid Pop and fertilizer - phosphoric acid Properties of Bases Bitter taste Change color of acid-base indicators (blue in pH paper) Dilute aqueous solutions feel slippery Ex. Soap Some react with acids to neutralize and form salt and water Some are electrolytes Examples of/


1 Acid Bases Chemistry. 2 Acid-Base Objectives 1. Identify the properties of acids and bases. 2. Classify solutions as acidic, basic, or neutral. 3. Compare.

36 Determining pH There are several ways to determine pH: 1. Indicators can be used to determine the approximate pH of a solution. -acid-base indicators: compounds whose colors are sensitive to pH ♦either weak acids or weak bases ♦come in many different colors ♦exact pH range colors also changes ~transition interval: pH range over which an indicator changes colors 37 2. pH paper is made from soaking the paper in/


Acids Arrhenius Model Produce hydrogen ions aqueous solution. HCl  H + (aq) + Cl - (aq) Acids you SHOULD know: Acids you SHOULD know: Strong Acids Hydrochloric.

is a good choice for the titration of a strong acid with a strong base, and phenolphthalein changes color at the equivalence point of a titration of a weak acid with a strong base. 19 Chemical dyes whose color are affected by acidic and basic solutions are called acid-base indicators. Indicators and Titration End Point Many indicators used for titrations are weak acids. – Each has its own particular pH or pH ranges/


19.4 Neutralization Reactions > 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Chemists use acid-base reactions to determine.

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. An indicator (HIn) is a weak acid or base that dissociates in a known pH range. Indicators work because their acid form and base form have different colors in solution. Acid-Base Indicators The acid form of the indicator (HIn) is dominant at low pH and high [H + ]. The base form (In − ) is dominant at high pH and high [OH − ]. 19.2 Hydrogen/


Chapter 15 Acid-Base Titration and pH 1. Solution Concentrations* Molarity – one mole of solute dissolved in enough solvent (water) to make exactly one.

several solutions were. You used litmus paper and pH paper (Hydrion) Acid-base indicators are sensitive to pH of acids and bases. They will change color as a result of the ions present. 31 In acidic solutions, an indicator will be one color (litmus turns red) and in basic solutions, an indicator will be another color (litmus burns blue). 32 Indicator Samples Methyl red, Bromthymol blue, Methyl orange, Phenolphthalein, Phenol red are/


Acid Base Titrations AP Chemistry Chapter 15. Titration Titrations are used to determine the amount of acid or base in a solution Titrant: the solution.

is the same as the equivalence point. Acid-Base indicators Used to detect the equivalence point in an acid- base titration These work on LeChatelier’s Principle HIn  H + + In - clear pink Changes in equilibrium result in color changes. Indicators are usually weak organic bases or acidsacid form has different color than conjugate base form. Indicators change colors at different pH’s. We select an indicator that changes color at the expected equivalence point. Equivalence/


19.4 Neutralization Reactions > 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Chemists use acid-base reactions to determine.

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. An indicator (HIn) is a weak acid or base that dissociates in a known pH range. Indicators work because their acid form and base form have different colors in solution. Acid-Base Indicators The acid form of the indicator (HIn) is dominant at low pH and high [H + ]. The base form (In − ) is dominant at high pH and high [OH − ]. 19.2 Hydrogen/


Week of 12/1/14. It’s 12/1/14, good morning! 7-5.6-- Distinguish between acids and bases and use indicators (including litmus paper, pH paper, and phenolphthalein)

a colorless chemical that turns magenta (bright pink) in a base, and stays colorless in neutral or acidic solutions. 3. Students need to know the indicator colors (magenta for base or colorless for acids or neutrals) for phenolphthalein. C. pH paper 1.Has a range of colors depending on the pH of the solution. 2.The color of the paper is compared to the chart of the vial/


Aim AB 1a What are the properties of Acids and Bases?

the soluble salts tend to be spectator ions Acid Base Indicators tell us how acid or basic a substance is See Table M for examples of various indicators The pH range on the chart represents the point that a color change will occur –Values to the left represent more acidic pHs –Values to the right represent more basic pHs Acid Base Indicator Examples 1.A solution leaves thymol blue a/


Acids and Bases Chemistry Lowell High School 2006-2007 2/20/07 to …

, HBr, NaOH Thursday, February 22, 2007 IndicatorsIndicators INDICATE pH via color  As the pH of the solution changes, the indicator molecule reacts to the presence of H + by rearranging itself and forming a different color.  There is no “ standard ” color for each pH. Red is not always acid, blue is not always base Thursday, February 22, 2007 Agenda  FYI’s  Quiz  Conjugate Acid/BaseIndicator Lab Friday, February 23, 2007 FYI/


Chapter 19 “Acids, Bases, and Salts”. Section 19.1 Acid-Base Theories n OBJECTIVES: –Define the properties of acids and bases.

given for a certain temperature (25 o C), thus may change at different temperatures –what if the solution already has a color, like paint? – the ability of the human eye to distinguish colors is limited Acid-Base Indicators n A pH meter may give more definitive results –some are large, others portable –works by measuring the voltage between two electrodes; typically accurate to within 0/


Acids, Bases, and Salts”. Warm Up n What is the difference between cohesion and adhesion? n What is the change in kinetic energy between a solid and.

given for a certain temperature (25 o C), thus may change at different temperatures –what if the solution already has a color, like paint? – the ability of the human eye to distinguish colors is limited Acid-Base Indicators n A pH meter may give more definitive results –some are large, others portable –works by measuring the voltage between two electrodes; typically accurate to within 0/


1 The Chemistry of Acids and Bases. 2 Acid and Bases.

.Determine the pH to the tenth and ion concentration of the following unknown solution given the color of each indicator:  Methyl Orange – yellowish orange  Chlorphenol Red – yellow  Bromthymol Blue – yellow  Bromcresol Green – blue 46 ACID-BASE REACTIONS Titrations H 2 C 2 O 4 (aq) + 2 NaOH(aq) ---> acid base acid base Na 2 C 2 O 4 (aq) + 2 H 2 O(liq) Carry out this reaction/


ACIDS and BASES pH indicators pH indicators are valuable tool for determining if a substance is an acid or a base. The indicator will change colors in.

.0 x 10 -7 M d. [OH-] = 1.0 x 10 -7 M basic acidic neutral Example #5 Which is the MOST basic from question #4? B. Acids and bases: Titrations The amount of acid or base in a solution is determined by carrying out a neutralization reaction; an appropriate acid-base indicator (changes color in specific pH range) must be used to show when the neutralization is completed/


ACIDS and BASES (unit 11) Notes start on slide 35 ***

in the eq. expression Finally, Calculate pH pH = -log [H + ] pH = -log (5.4 x 10 -5 ) pH = -(-4.27) pH = 4.27 Acids and bases: Titrations The amount of acid or base in a solution is determined by carrying out a neutralization reaction; an appropriate acid-base indicator (changes color in specific pH range) must be used to show when the neutralization is completed. Buret Solution with/


1 The Chemistry of Acids and Bases. 2 Acid and Bases.

.Determine the pH to the tenth and ion concentration of the following unknown solution given the color of each indicator:  Methyl Orange – yellowish orange  Chlorphenol Red – yellow  Bromthymol Blue – yellow  Bromcresol Green – blue 50 ACID-BASE REACTIONS Titrations H 2 C 2 O 4 (aq) + 2 NaOH(aq) ---> acid base acid base Na 2 C 2 O 4 (aq) + 2 H 2 O(liq) Carry out this reaction/


Indicators and pH Meters Acid-base indicators are compounds whose colors are sensitive to pH. Indicators change colors because they are either weak acids.

Acid-base indicators are compounds whose colors are sensitive to pH. Indicators change colors because they are either weak acids or weak bases. Chapter 15 Section 2 Determining pH and Titrations HIn and In − are different colors. In acidic solutions, most of the indicator is HIn In basic solutions, most of the indicator is In – Indicators and pH Meters The pH range over which an indicator changes color is called its transition interval. Indicators that change color/


Chapter 14 Chemical Compounds Preview Section 1 Ionic and Covalent CompoundsIonic and Covalent Compounds Section 2 Acids and BasesAcids and Bases Section.

to identify an unknown chemical. Like acids, many bases are corrosive. Section 2 Acids and Bases Chapter 14 Bases and Their Properties, continued Bases Change Color in Indicators Like acids, bases change the color of an indicator. Most indicators turn a different color in the presence of bases than they do in the presence of acids. For example, bases change the color of red litmus paper to blue. Section 2 Acids and Bases Chapter 14 Bases and Their Properties, continued When/


Acids/Bases/Salts Properties. Properties  electrolytes  turn litmus red  sour taste  react with metals to form H 2 gas  slippery feel  turn litmus.

equals mole ratio required by reaction Determined by… Determined by… indicator color changeindicator color change B. Titration dramatic change in pHdramatic change in pH B. Titration moles H 3 O + = moles OH - M  V  n = M  V  n M:Molarity V:volume n:# of H + ions in the acid or OH - ions in the base B. Titration  42.5 mL of 1.3M KOH are/


Chapter 15 Acid-Base Theories. Properties of Acids and Bases Acids –Give foods a tart or sour taste What acidic foods might you eat? –Aqueous solutions.

to two decimal places –Rules are due to the sensitivity of pH meters Acid-Base Indicators Dyes An indicator (HIn) is an acid or base that undergoes dissociation in a known pH range –An indicator is a valuable tool for measuring pH because its acid form and base form have different colors in solution –The acid form of the indicator dominates the disassociation equilibrium at low pH –The basic form of the/


Chapter 8 Solutions, Acids, and Bases Section 8.1 Formation of Solutions Section 8.2 Solubility and Concentration Section 8.3 Properties of Acids and Bases.

Taste, Slippery Feel, and Color Changes in Indicators Identifying Bases: Bitter Taste, Slippery Feel, and Color Changes in Indicators Many cough syrups and other liquid medicines contain similar bases. Many cough syrups and other liquid medicines contain similar bases. Bases feel slippery. Bases feel slippery. Turn red litmus paper blue; can also use phenolphthalein (acid-base indicator) Turn red litmus paper blue; can also use phenolphthalein (acid-base indicator) Solution w/ base phenolp. =red; solution w/


Chapter 16 “Acids, Bases, and Salts” Adapted & Modified from: Pre-AP Chemistry Charles Page High School Stephen L. Cotton.

given for a certain temperature (25 o C), thus may change at different temperatures –what if the solution already has a color, like paint? – the ability of the human eye to distinguish colors is limited Acid-Base Indicators  A pH meter may give more definitive results –some are large, others portable –works by measuring the voltage between two electrodes; typically accurate to within 0.01/


Chapter 19 “Acids, Bases, and Salts”. Section 19.1 Acid-Base Theories n OBJECTIVES: –Define the properties of acids and bases.

given for a certain temperature (25 o C), thus may change at different temperatures –what if the solution already has a color, like paint? – the ability of the human eye to distinguish colors is limited Acid-Base Indicators n A pH meter may give more definitive results –some are large, others portable –works by measuring the voltage between two electrodes; typically accurate to within 0/


Copyright © Houghton Mifflin Company. All rights reserved.14–1 Acids, Bases, and AcidBase Equilibria.

© Houghton Mifflin Company. All rights reserved.14–74 pH 0 1 2 3 4 5 6 pH 7 8 9 10 11 12 13 INDICATORS Indicators signal change in PH Universal paper indicator: Range and Color Changes of Some Common Acid-Base Indicators Indicators pH Scale 1234567891011121314 Methyl orange red 3.1 – 4.4 yellow Methyl red red 4.4 6.2 yellow Bromthymol blue yellow 6.2/


Acid-Base Equilibria Arrhenius Definition Acids are substances that produce hydrogen ions when dissolved in water. Acids are substances that produce.

% neutralization. [H + ] = [OH - ] End point: Change in color of indicator End point: Change in color of indicator Half Equivalence point: 1/2 total amount of titrant added. Buffer solution pH = pK a Half Equivalence point: 1/2 total amount of titrant added. Buffer solution pH = pK a Titrations As acid or base is added, there is As acid or base is added, there is Very little change in/


Acids and Bases

7 8 9 10 11 12 Indicator Acid color Transition color Base color Methyl orange Bromphenol blue STRONG ACID – WEAK BASE pH INDICATOR COLORS IN TITRATION 1 2345 6 789101112 Indicator Phenolphthalein Methyl Red Orange IV ColorlessPinkRed OrangeYellow OrangePeachYellow pH phenolphthalein methyl red methyl orange Indicator Colors in Titration Common pH Indicators Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 520 Edible Acid-Base Indicators COLOR CHANGES AS A FUNCTION OF pH INDICATOR pH 2 3 4 5 6/


Acids, Bases, & pH. RB topic 10 1. Define an electrolyte: a substance that conduct an electric current (due to dissociation of ionic substance via.

the solution in the beaker? ____________________________ For each acid-base indicator on reference table M, color the chart below to indicate appropriate color of the indicator from pH 1 to 14: Titration I. Definitions 1.) A TITRATION is used to determine the [ ], or molarity, of an unknown acid or base through neutralization 2.) Careful neutralization is performed using an acid or a base of KNOWN molarity called a STANDARD 3.) If/


Acids, Bases, and Salts”. Section 19.1 Acid-Base Theories n OBJECTIVES: –Define the properties of acids and bases.

given for a certain temperature (25 o C), thus may change at different temperatures –what if the solution already has a color, like paint? – the ability of the human eye to distinguish colors is limited Acid-Base Indicators n A pH meter may give more definitive results –some are large, others portable –works by measuring the voltage between two electrodes; typically accurate to within 0/


Chapter 19 “Acids, Bases, and Salts” Pre-AP Chemistry Charles Page High School Stephen L. Cotton.

given for a certain temperature (25 o C), thus may change at different temperatures –what if the solution already has a color, like paint? – the ability of the human eye to distinguish colors is limited Acid-Base Indicators n A pH meter may give more definitive results –some are large, others portable –works by measuring the voltage between two electrodes; typically accurate to within 0/


Properties of Acids n Acids taste sour, will change the color of an acid-base indicator, and can be strong or weak electrolytes in aqueous solution.

Properties of Acids n Acids taste sour, will change the color of an acid-base indicator, and can be strong or weak electrolytes in aqueous solution. Properties of Acids n Sour/tart acetic acid citric acid Properties of Acids Blue litmus paper turns red in contact with an acid (and red paper stays red). n Change color of acid/base indicator Properties of Acids n Strong/weak electrolytes –Electrolytes are solutions that conduct electricity. Properties of Acids n/


Chapter 19 “Acids, Bases, and Salts” Pre-AP Chemistry Charles Page High School Stephen L. Cotton.

given for a certain temperature (25 o C), thus may change at different temperatures –what if the solution already has a color, like paint? – the ability of the human eye to distinguish colors is limited Acid-Base Indicators n A pH meter may give more definitive results –some are large, others portable –works by measuring the voltage between two electrodes; typically accurate to within 0/


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