Preparation of Solutions (cont.)

Procedure Checklist 6-1:Procedure Checklist 6-1: Calculating by the Proportion Method

1. Write a conversion factor with the • units needed in the numerator or

before the colon;

• units converting from in the denominator or after the colon.

Preparation of Solutions (cont.)

Procedure Checklist 6-1: Procedure Checklist 6-1: (cont.)(cont.)

2. Write a factor • with the unknown, “X,” in the numerator or

before the colon .

• with the number to convert in the denominator or after the colon.

X/B or X:B

Procedure Checklist 6-1:Procedure Checklist 6-1: (cont.)(cont.)

3. Set the two factors up as a proportion.

4. Cancel units.

5. Cross-multiply or multiply the means and extremes and solve for the unknown value.

Using Conversion Factors: Proportion Method (cont.)

X/B = C/D or X:B = C:D

Preparation of Solutions (cont.)

Calculate the amount of NaCl needed for for 250 mL of 0.9% sodium chloride.

0.9 g NaCl in 100 mL solution

Step A Convert

No conversion is needed.

ExampleExample

Preparation of Solutions (cont.)

0.9 g NaCl in 100 mL solution

Step B Calculate using the proportion method.

0.9 g /100 mL = X/250 mL

0.9 g x 250 = 100 x X

225 g/100 = 100X/100

2.25 g NaCl = X

ExampleExample

Preparation of Solutions (cont.)

Step C Think!...Is It Reasonable?

Since there is 0.9 g of NaCl in 100 mL, there should be more than 2 times that amount in 250 mL, so 2.25 g is a reasonable answer.

ExampleExample

Preparation of Solutions (cont.)

Procedure Checklist 6-2:Procedure Checklist 6-2: Calculating by Dimensional Analysis

1. Write the unknown “X” on one side of the equation.

X =

Preparation of Solutions (cont.)

Procedure Checklist 6-2Procedure Checklist 6-2 (cont.)(cont.)

2. On the other side of the equation, write a conversion factor with the units of measure for the answer on top and the units you are converting from on the bottom.

mL

g. x

100

90

Preparation of Solutions (cont.)

Procedure Checklist 6-2 Procedure Checklist 6-2 (cont.)(cont.)

3. Multiply the numerator of the conversion factor by the number that is being converted divided by 1.

1

250

100

90 mLX

mL

g.x

Preparation of Solutions (cont.)

Procedure Checklist 6-2 Procedure Checklist 6-2 (cont.) (cont.)

4. Cancel units.

1

250

100

90 mLX

mL

g.x

Preparation of Solutions (cont.)

Procedure Checklist 6-2:Procedure Checklist 6-2:5. Solve the equation.

gX

100

225

g.X 252

Preparation of Solutions (cont.)

Step C Think! … Is It Reasonable?

Regardless of the method used, we find that 2.25 g of NaCl is needed to prepare 250 mL of a 0.9% solution.

ExampleExample

Preparation of Solutions (cont.)

Write the recipe for 250 mL of 0.9% sodium chloride solution.

ExampleExample

0.9% Sodium Chloride Solution

NaCl 2.25 g

Water qsad 250 mL

Practice

Write a recipe for preparing 50 g if a 10% zinc oxide ointment using zinc oxide powder and petrolatum jelly.

ANSWER:

10% Zinc Oxide Ointment

Zinc oxide powder 5g

Petroleum jelly 45 g

Preparing a Dilution from a Concentrate

• When preparing a solution from two solutions of different concentration, know

– Solvent – less concentrated solution

– Solute – more concentrated solution

• To calculate, use

– Formula method

– Alligation

Preparing a Dilution from a Concentrate (cont.)

Procedure Checklist 16-1 Procedure Checklist 16-1 Formula Method

1. Identify information needed:

a. V = volume of solution needed

b. C = concentration of solution needed

c. St = amount of solute

d. Sv = amount of solvent

Preparing a Dilution from a Concentrate (cont.)

Procedure Checklist 16-1 Procedure Checklist 16-1 (cont.)

2. Insert values into formula:

C x V = St

3. Determine the amount of solvent by subtracting the solute from the total volume:

V – St = Sv

Preparing a Dilution from a Concentrate (cont.)

Ordered: 1 oz of ¼ strength hydrogen peroxide in normal saline for wound care TID for 2 days. Write the recipe.

Step A = Convert ounces to mL.

1 oz TID x 2 day = 6 oz

1oz/30 mL = 6 oz/ X

180 mL = X

ExampleExample

Preparing a Dilution from a Concentrate (cont.)

Step B Calculate.

V = 180 mL, C = ¼

C x V = St ¼ x 180 mL = 45 mL of the solute (hydrogen peroxide)

V – St = Sv

180 mL – 45 mL = 135 mL of the solvent (normal saline)

ExampleExample

Preparing a Dilution from a Concentrate (cont.)

The recipe is:

Step C

Since 45 is one fourth of the total volume of solution (180 mL) and 135 + 45 = 180 mL, this answer is reasonable.

ExampleExample

¼ strength Hydrogen Peroxide – 180 mL

H2O2 45 mL

NS 135 mL

Practice

Clean leg wound with 2 oz of ½ strength hydrogen peroxide in normal saline q6 h x 3 days. Write the recipe for total supply needed.

½ hydrogen peroxide – 720 mL

H2O2 360 mL

NS 360 mL

ANSWER: