pH of Orange Juice 1

Measuring the pH of Orange JuiceMeasuring the pH of Orange Juice

pH of Orange Juice 2

What is pH?What is pH? pH is a measure of the concentration of hydrogenpH is a measure of the concentration of hydrogen ions (Hions (H++) in grams/1000 ml of water) in grams/1000 ml of water

The pH scale ranges from 1 to 14The pH scale ranges from 1 to 14

number 7 represents a neutral solutionnumber 7 represents a neutral solution

numbers below 7 show an acidic solutionnumbers below 7 show an acidic solution

numbers above 7 show a basic solutionnumbers above 7 show a basic solution

pH of Orange Juice 3

pH of Common SubstancespH of Common Substances

pH of Orange Juice 4

How is the pH scale made?How is the pH scale made? The pH scale is “logarithmic”The pH scale is “logarithmic”

Each whole value of pH below 7 is ten timesEach whole value of pH below 7 is ten times MORE ACIDIC than the next lower wholeMORE ACIDIC than the next lower whole number:number: - - pH 4 is 10 times more acidic than pH 5pH 4 is 10 times more acidic than pH 5 -- pH 4 is 100 times more acidic than pH 6pH 4 is 100 times more acidic than pH 6 - pH 4 is 1000 times more acidic than pH 7- pH 4 is 1000 times more acidic than pH 7

Each whole value of pH above 7 is ten timesEach whole value of pH above 7 is ten times MORE ALKALINE (basic) than the next higherMORE ALKALINE (basic) than the next higher whole number:whole number: - pH 10 is 10 times more basic than pH 9- pH 10 is 10 times more basic than pH 9 - pH 10 is 100 times more basic than pH 8- pH 10 is 100 times more basic than pH 8 - pH 10 is 1000 times more basic than pH 7- pH 10 is 1000 times more basic than pH 7

pH of Orange Juice 5

What does the pH scale look like?What does the pH scale look like?

The mathematical equation for pH is:The mathematical equation for pH is:pH = - log (concentration of H+)pH = - log (concentration of H+)

grams/Liter

grams/Liter

pH of Orange Juice 6

How do we measure pH?How do we measure pH? There are several ways to measure pHThere are several ways to measure pH

1.1. ph Meterph Meter

A digital readout givesA digital readout gives the pH directly.the pH directly.

This meter has a specialThis meter has a special built-in electrodebuilt-in electrode placed in the solution. placed in the solution.

A pH meter is the most accurate, but most expensive methodA pH meter is the most accurate, but most expensive method

pH of Orange Juice 7

2. pH Paper2. pH Paper

Paper strip on a rollPaper strip on a roll shows differentshows different colors forcolors for each pH unit.each pH unit.

pH MeasurementspH Measurements

pH paper is the least accurate, but cheapest methodpH paper is the least accurate, but cheapest method

pH of Orange Juice 8

3. pH Test Strips3. pH Test Strips

Test strips showTest strips show different colors fordifferent colors for pH in fractionspH in fractions of a pH unit over aof a pH unit over a narrow range.narrow range.

pH MeasurementspH Measurements

We will use pH strips because they areWe will use pH strips because they aremore accurate than pH papermore accurate than pH paper

pH of Orange Juice 9

Prepare Orange Juice SolutionsPrepare Orange Juice Solutions1. Using a thawed can of frozen orange juice, make1. Using a thawed can of frozen orange juice, make a batch of juice that you would normally drink –a batch of juice that you would normally drink – 3 cans of tap water plus 1 can of frozen juice3 cans of tap water plus 1 can of frozen juice LABEL THIS 100% OJLABEL THIS 100% OJ

2. Measure 50 ml of the 100% OJ into a 500 ml2. Measure 50 ml of the 100% OJ into a 500 ml graduated Erlenmeyer flask and fill with tapgraduated Erlenmeyer flask and fill with tap water to the 500 ml mark.water to the 500 ml mark. LABEL THIS 10% OJLABEL THIS 10% OJ

3. Repeat step 2 using 25, 10, 5, and 2.5 ml of 100% 3. Repeat step 2 using 25, 10, 5, and 2.5 ml of 100% OJ - LABEL THESE 5%, 2%, 1%, and 0.5% OJOJ - LABEL THESE 5%, 2%, 1%, and 0.5% OJ

pH of Orange Juice 10

Measure pH of OJ SolutionsMeasure pH of OJ Solutions1. Pour about 50 ml of the 100% OJ into a 100 ml1. Pour about 50 ml of the 100% OJ into a 100 ml beaker and label it. Repeat with the 10%, 5%,beaker and label it. Repeat with the 10%, 5%, 2%, 1% and 0.5% solutions.2%, 1% and 0.5% solutions.

2. Hold the white end of a 4070 test strip and dip it2. Hold the white end of a 4070 test strip and dip it into one of the solutions prepared in 1 above tointo one of the solutions prepared in 1 above to about ½-inch for 2 seconds.about ½-inch for 2 seconds.

3. Shake off excess liquid and match the color of the3. Shake off excess liquid and match the color of the strip to the color chart before it dries. Record strip to the color chart before it dries. Record the pH value on the data table.the pH value on the data table.

4.4. Repeat the process with all the solutions and Repeat the process with all the solutions and the tap water.the tap water.

pH of Orange Juice 11

pH vs. OJ concentrationpH vs. OJ concentrationData TableData Table

OJ ConcentrationOJ Concentration pH pH

0.0% (tap water)0.0% (tap water) ______________ 0.5%0.5% ______________ 1.0%1.0% ______________ 2.0%2.0% ______________ 5.0%5.0% ______________10.0%10.0% ______________

pH of Orange Juice 12

Graphing the ResultsGraphing the Results

Make a graph of the results using “semi-log”Make a graph of the results using “semi-log”paper – this paper has a logarithmic scalepaper – this paper has a logarithmic scaleon the y-axis and a linear scale on the x-axis.on the y-axis and a linear scale on the x-axis.

Show the OJ Concentration on the y-axisShow the OJ Concentration on the y-axisand the pH value on the x-axis.and the pH value on the x-axis.

pH of Orange Juice 13

Semi-log Paper for Graphing ResultsSemi-log Paper for Graphing Results

pH of Orange Juice 14

QuestionsQuestions

1.1. Which solution is the most acidic?Which solution is the most acidic?

2.2. What is the pH of tap water?What is the pH of tap water?

3.3. Using the graph, predict the pH valueUsing the graph, predict the pH value of a 50% OJ solution.of a 50% OJ solution.