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Concentration Measurement: Percent and PPM

Mr. Shields Regents Chemistry U12 L03

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Percent Concentration (V/V)Percent Concentration (V/V)

The two “Percent” methods for measuring Concentration are Volume/Volume (V/V) and Mass/Mass(m/m).

Let’s look at the V/V method 1st:

The formula for % Concentration (V/V) is:

Percent (V/V) = Volume of solute x 100 Volume of Solution

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Percent Concentration (V/V)Percent Concentration (V/V)Using Percent (V/V) to specify Concentration is used when BOTH the solute and solvent are liquids

Example: water + vinegar (H20 + CH3COOH)

It also assumes no INTERACTION (i.e. reaction) betweenThe solute and the solvent.

And notice that we are dividing the volume of the SOLUTE By the volume of the SOLUTION – not the other way around

Percent (V/V) = Volume of Solute x 100 Volume of Solution

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Percent Concentration (V/V)Percent Concentration (V/V)

V/V solution concentrations tells us what % of solute ispresent in the solution. Doubling the amount of solute willNot necessarily double the % V/V. As we add solute to thesolvent the volume of the solvent also increases.

AND REMEMBER ! It is essential to express both theSolute and the solution volumes in the SAME UNITS.For example Liters and Liters or Milliliters and Milliliters,

% V/V = 3/9 = 33% % V/V = 6/12 = 50%% V/V = 3/9 = 33% % V/V = 6/12 = 50%

How much solute and solvent is present in each?

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Percent (V/V) ProblemPercent (V/V) Problem27 ml of ethanol are dissolved in 270 ml of Octane.What is the % Concentration of Ethanol?

% Conc. (V/V) = 27 ml x 100 = 9.1% (27 + 270)

What is the concentration in % (V/V) if 1.5 ml of VinegarIs dissolved in 30 ml of water?

% conc. of vinegar (V/V) = 1.5 ml x 100 = 4.76 % (1.5 + 30)

Note: Vinegar bought at the store is about a 5% sol’n

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Percent Concentration Percent Concentration (m/m)(m/m)

Percent Concentration by mass, % (m/m), is calculated veryMuch like the % (v/v) method:

Percent (m/m) = Mass of solute x 100 Mass of Solution

NOTE it’s the mass of the Solution and NOT the just theSolvent.

As in v/v calculations the totalsolution is equal to the sum ofBoth the Solute and the Solvent +mass mass mass

=

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Percent (m/m) ProblemPercent (m/m) Problem1) What is the % Concentration (m/m) of I2 if 16.7g of I2Are dissolved in 250g of ethanol?

% Conc. (m/m) = 16.7g x 100 = 6.26% (16.7g + 250g)

2) 24g of AgNO3 were dissolved in 125ml of water. WhatIs the % concentration (m/m) of AgNO3 in solution?

Desity of H2O = 1g/ml; the mass of the water = 125g

Conc. of AgNO3 (m/m) = 24g x 100 = 16.1% (24 + 125)

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PPMPPMThe last method of expressing sol’n concentrationsQuantitatively is PARTS PER MILLION (i.e. ppm)

This method is used extensively in theEnvironmental Field. Why is this the case?

It’s a method that allows one to easily comprehend the Concentration of extremely small amounts of solute inSolvent.

So we might find for example that a sample of drinkingWater contains 3.2 ppm of Arsenic and compare that to the allowable levels of As in drinking water (0.05 ppm)

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PPMPPM

If the allowable limits of As in drinking water is 0.05 ppm,What does this mean in terms of concentration?

- First, 1 ppm means 1 part in 1 million (106) parts

So, if the acceptable level of As is 0.05 ppm then for every 5 Molecules of As moleculesallowed in drinking water there must be100,000,000 (108) molecules of water.

Expressed another way we could say… - for every 5g of As there must be 100,000,000g of H20!

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PPM CalculationsPPM Calculations

How do we calculate ppm? We’ll use this equation…

ppm of solute = Mass of Solute x 106 Mass of Solution

Notice that again we are dealing with the TOTAL massOf the solution.

Let’s look at an example…

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PPM CalculationsPPM CalculationsA 6.5g sample of well water is found to contain3.5 x 10-6g of Pb+2. What is the concentration of lead In the well water in ppm?

PPM Lead = mass of the solute x 106

mass of the solution

PPM Lead = 3.5 x 10-6g x 106

6.5g

PPM Lead = 0.538 ppm

Is this the total mass?Why can we use it?

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PPM CalculationsPPM Calculations

What is the concentration in ppm of NaCl in water if1.2g is dissolved in 240 ml of water?

PPM NaCl = mass of the solute x 106

mass of the solution

PPM NaCl = 1.2g x 106 = 4975.1 ppm (1.2 +240)g

The salinity of sea water is about35,000 ppm

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PPM CalculationsPPM Calculations

What if we hadn’t added in the 1.2g of NaCl to theMass of solvent (240g). Would it have made a difference? Let’s check it out …

PPM NaCl = mass of the solute x 106

mass of the solution

PPM NaCl = 1.2g x 106 = 5000 ppm 240g

YES! It would have made a difference 5000ppm vs 4975ppmSo always add in the mass of the Solute to the solventif it is a Significant amount

Mass of solvent ONLY

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PPM CalculationsPPM CalculationsWhat if we had only added in 1.2 mg of NaCl to 240 ml Of water. Does it make much difference if we add theMass of the salt to the solvent?Calculate it both ways and see …

PPM NaCl = 0.0012g x 106 = 4.999975ppm (0.0012 + 240)g

PPM NaCl = 0.0012g x 106 = 5.000000ppm 240g

Are these two numbers significantly different?

No, not really! So here we could have ignored the massOf the salt

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Global Warming is blamed on the increase in CO2 Levels in the atmosphere.

A) How much did CO2 increase in both ppm and %between 1957 and 2000?

16.98% increase in CO2

B) In 2000 whatWas the Percent by Volume of CO2

In the atmosphere?

O.037%

372 X 100 =106

(372-318)/318 x 100

54 ppm increase or