Preparation of solution

TECHNIQUES IN CHEMISTRY LABORATORY

SKL 1023DR.LEE TIEN TIEN

GROUP B

NAME MATRIX NO

NORSYAFIQAH BT ROSLI E20121004959

ATHIFAH BT ISMAIL E20121003644

AZURA BT CHE AZMI E20121004984

FATEN NADIA BT MASRI E20121004999

SITI SHAHRIFFAH NORAINY BT SAHRANI

E20121004927

ADRINA BT KASIM E20121004962

What should we learn?

Preparing solution of target

concentration

Correct apparatus for preparing

solution

Safety precautions in preparing

of solution

Proper method in transferring

and handling solution

Introduction to preparing solutionMany experiment involving chemicals

call for their use in solution from. That is, two or more substances are mixed together in known quantities.

This may involve weighing a precise amount of dry material or measuring a precise amount of liquid.

Preparing solutions accurately will improve an experiment’s safety and chances for success.

Let’s understand the terms !!

solute

•Substance which dissolves in a solution

solvent

•Substance which dissolves another to form a solution

•Example: water is the solvent

Continue….

solution

•Mixture of two or more pure substances

mole

•The amount of pure substance containing the same number of chemical units

•1mole is 6.02 X 1023 molecules of that substance

Safety precaution in preparing solution

Check the label on all chemical bottles twice before removing any of the contents

Make sure all chemicals are clearly and currently label with the correct name and concentration

Continue…

Never return any unused chemicals to their original container

Treat any chemical as if it is HAZARDOUS

Measurements and Significant Digits

One of the most important requirements of a good scientist is the ability to properly record measurements to the correct number of significant digits and with the correct units. Examples of the types of volumetric glassware and instruments encountered in the laboratory are given below with directions on how to correctly record measurements.

Apparatus are Commonly used in Preparation of Solution

Beaker

Not designed to accurately measure

volumes of liquids.

Designed to hold a particular amount of liquid

come in various sizes with different

calibrations

These measurements

have a ±5% error and are therefore approximations.

An examination of the 100-mL beaker shown reveals calibration lines every 10 mL between 20 and 80 mL. These measurements have a ±5% error and are therefore approximations.

The 250-mL beaker has calibration lines every 25 mL between 25 and 200 mL. The error again is ±5%. The amount of liquid in the beaker is therefore 125 mL ±5%.

Erlenmeyer flask

Not designed to accurately measure

volumes of liquids.

useful for stirring solutions during

titrations and synthetic work.

most common sizes of erlenmeyer flasks probably are 250 ml

and 500 ml.

also designed to hold a particular amount of liquid

Erlenmeyer flasks come in various sizes. An examination of the 250-mL flask shown gives calibration lines every 25 mL between 50 and 200 mL. These measurements have a ±5% error and are therefore approximations.

The 500-mL Erlenmeyer flask has calibration lines every 50 mL between 200 and 500 mL. The error again is ±5%. The amount of liquid in the flask is therefore 500 mL ±5%.

Graduated cylinder

calibrated to contain (TC) or

to deliver (TD) a precise amount

of liquid

more accurate and precise than

flasks and beakers for this

function

Tolerances vary with the size of the graduated

cylinder.

Tolerances may or may not be

given at the top of the cylinder

neck. If not shown, use one

half interval division.

The 50-mL graduated cylinder shown has 1-mL divisions and a tolerance of ±0.50 mL and is calibrated to contain the measured volume.

A graduated cylinder marked TC will hold the volume measured but will not deliver that volume to the container when transferred. Some of the liquid will remain behind in the graduated cylinder. If an exact amount is to be transferred, the graduated cylinder should be marked. TD.

MEASUREMENTS: Water and aqueous solutions will form a concave meniscus when placed in a graduated cylinder as the water molecules are more strongly attracted to the glass than each other.  The bottom of the curved surface is read at eye level and the volume measurement is read to the proper number of significant digits. 

Determine the smallest division marked on the graduated cylinder: (1) find two adjacent markings that have a numeric label, (2) subtract and divide by the number of divisions between the numeric labels.

Numbers are scaled to increase from bottom to top of the graduated cylinder. Using the scale markings, determine the value of the certain digits.

Estimate the distance the meniscus lies between markings as a decimal fraction. Multiply the fraction times the division increment from Step 1. Add this to the certain digits to provide the uncertainty in the measurement.

Follow this step to make volume measurement with proper number of significant figure

EXAMPLE 1 

Step 1.  The labeled scale markings are 8 mL and 6 mL. There are 10 divisions between the numeric labels.  [(8-6)/10] mL = 0.2 mL is the increment value.

Step 2.  The first certain digit is 6 mL since the meniscus is below 8 mL.  There are three smaller scale divisions below the meniscus: 3 x 0.2 mL/division = 0.6 mL  The known digits are (6 + 0.6 ) mL = 6.6 mL

Step 3.  The meniscus lies 0.1 of the distance between the markings: 0.1 x 0.2 mL = 0.02 mL  The volume should be recorded as (6.6  + 0.02) mL = 6.62 mL

Burette

•A burette, is a uniform-bore glass tube with fine gradations and a stopcock at the bottom, used especially in laboratory procedures for accurate fluid dispensing and measurement. 

•Like graduated cylinders, burettes come in various volume sizes.

•Care must be taken when filling the burette that the tip contains no air bubbles.

•The burette is commonly used in titrations to measure precisely how much liquid is used.

measurement

Water and aqueous solutions will form a concave meniscus when placed in a burette similar to a

graduated cylinder

The bottom of the curved surface is read at eye level and the volume measurement is

read to the proper number of

significant digits.

Use the steps given for graduated cylinders to make the volume

measurement with the proper number of significant digits

Note that, unlike the graduated cylinder, the numbers are

scaled to increase from top to bottom.

EXAMPLE 1

Step 1. The labeled scale markings are 14 mL and 15 mL. There are 10 divisions between

the numeric labels. [(15-14)/10] mL = 0.1 ml is the increment value.

Step 2. The first certain digit is 14 mL since the meniscus is below 14 mL. There are zero smaller scale division

above the meniscus: 0 x 0.1 mL/division = 0.0 mL The

known digits are (14 + 0.0 ) mL = 14.0 mL

Step 3. The meniscus lies 0.5 of the distance between the

markings: 0.5 x 0.1 mL = 0.05 mL The volume should be

recorded as (14.0 + 0.05) mL = 14.05 mL

A pipette is a type of chemical dropper used in laboratory experiments to measure and transport fixed volumes of chemicals

Volumetric flasks are calibrated to contain a  precise volume of solution

and are, therefore, often used to prepare solutions needed for

quantitative analysis.

The neck of the flask has a calibration mark to indicate the fill level for the

volume of solution needed.

The bottom of the meniscus is lined up with this mark to insure accuracy. 

Volumetric Flasks

The flask can also be used for dissolving substances in specific

liquids.

This method is carried out if someone wants to find out what

solutions can be produced if particular liquids and substances

are mixed together.

This flask is also used when two different liquids are chosen to be

mixed together.

MEASUREMENTS: Note the volume given on the volumetric flask. Tolerances are usually within a few hundredths of a mL. When filled to the calibration mark, the flask

shown would contain 100.00 mL (0.10000 L) of solution.

Technique

An electronic balance is a device used to find accurate measurements of weight. It is used very commonly in laboratories for weighing chemicals to ensure a precise measurement of those chemicals for use in various experiments.

PREPARATION OF SOLUTION FROM SOLID

PREPARATION OF SOLUTION FROM SOLID

This is how to make a chemical solution using a solid dissolved in a liquid, such as water or alcohol.

If you don't need to be very accurate, you can use a beaker or Erlenmeyer flask to prepare a solution.

More often, you'll use a volumetric flask to prepare a solution so that you'll have a known concentration of solute in solvent.

STEPS OF PREPARATION OF SOLUTION FROM SOLID

STEP 1

•Weight out the solid that is your solute .

STEP 2

•Fill the volumetric flask about halfway with distilled water or deionized water (aqueous solutions) or other solvent.

•Volumetric flasks are used to accurately prepare solutions for chemistry.

STEP 3

•Transfer the solid into the small beaker or volumetric flask.

•More easier to dissolve the solid if transfer to the small beaker than the volumetric flask.

•Use the funnel to transfer the solid or the solution into the volumetric flask.

STEP 4

•Rinse the weighing dish and the funnel with the water to make certain all of the solute is transferred into the flask.

STEP 5

•Stir or swirl the solution until the solute is dissolved. You may need to add more water (solvent) or apply heat to dissolve the solid.

STEP 6

•Fill the volumetric flask to the mark with distilled or deionized water.

•Closed tightly with stopper and invert several time to get homogeneous solution.

HOW TO GET PRECISE AMOUNT OF SOLUTION

Many experiments involving chemicals substances for their use in solution form.

That is, two or more substances are mixed together in known quantities.

This may involve weighing a precise amount of dry material or measuring a precise amount of liquid.

Preparing solutions accurately will improve an experiment's safety and chances for success.

Solution 1: Using percentage by weight (w/v)

Formula : The formula for weight percent (w/v)

is:

[Mass of solute (g) / Volume of solution (mL)]x 100

ExampleA 10% sodium chloride (NaCl) solution has 10g of NaCl dissolved in 100 mL of solution.

STEPS : Weight 10g of NaCl.

Pour it into a graduated cylinder or volumetric flask containing about 80mL of water.

Once the NaCl has dissolved completely (swirl the flask gently if necessary), add water to bring the volume up to the final 100 mL.

Solution 2: Molar Solutions

Molar solutions are the most useful in chemical reaction calculations because they directly relate the moles of solute to the volume of solution.

Formula: The formula for molarity (M) is:

or

Example :How much sodium chloride is needed to make 1 liter of an aqueous 1 M solution?

• First, calculate the molecular weight (MW) of sodium chloride.STEP

1

• Checking the Periodic Table of Elements, find that the atomic weight of sodium (Na) is 23 and the atomic weight of chlorine (Cl) is 35.5.

STEP 2

Therefore, the molecular weight of sodium chloride (NaCl) is:

Na (23) + Cl (35.5) = 58.5 grams/mole

• To make a 1M aqueous solution of NaCl, dissolve 58.5 grams of NaCl in some distilled deionized water

STEP 3

• Then add more water to the flask until it totals 1 liter.STEP

4

To make molar NaCl solutions of other concentrations dilute the mass of salt to 1000ml or 1 liter of solution as follows:

0.1M NaCl solution requires:0.1 x 58.44 g of NaCl = 5.844g

0.5M NaCl solution requires: 0.5 x 58.44 g of NaCl = 29.22g

2M NaCl solution requires:2.0 x 58.44 g of NaCl = 116.88g

Preparation of Solution Through Dilution Method

Concentration =

What we need to know?

Concentration of Solution:

Expression of Concentration:

The amount of solute that dissolved in a certain amount of solution.

Molarity =

•Unit of concentration: Molarity (M)

Formula to calculating dilution:M1V1 = M2V2 or C1V1 = C2V2

where: M1 = Molarity before dilution

C1 = Concentration before dilution

M2 = Molarity after dilution

C2 = Concentration after dilution

V1 = Volume before dilution

V2 = Volume after dilution

Steps that should be taken in preparation of solution :

STEP 3Calculate volume of starting solution required using equation M1V1 = M2V2 .

(Note: V1 must be in the same units as V2).

STEP 2

Determine the molarity of starting.STEP 1

Decide the volume and molarity of the final solution should be.(Volume can be expressed in liters or milliliters).

Example:

Prepare 100mL of 1.0M hydrochloric acid, HCl from concentrated (1.21M) hydrochloric acid, HCl.

  Solution: M1V1 = M2V2

(12.1M)(V1) = (1.0M)(100mL)

V1 = 8.26 mL conc. HCl

  Thus, we need 8.26mL from stock of 1.21M

HCl to prepared 100mL of a 1.0M of HCl.

How to prepared dilution from the laboratory ?Take out the 8.26mL

of 1.21M HCl from the stock. (By using

a pipette)

Transfer to the 100mL volumetric

flask.

Fill in the volumetric flask with distilled water until it nearly to calibration mark.( Used a dropper to make the dilution exactly to the calibration mark)Closed tightly with stopper and invert several time to get homogeneous solution.

Thank you…

For listening and your attention…