Chapter 1.2 Part A: Chemical Apparatus Grade 10 (Level L)

1.2.1 Names and uses of chemical apparatus

• Pipette: To measure specific amounts of liquid (e.g. exactly 10 cm3, exactly 25 cm3, etc., to the nearest 0.05 cm3).
• Burette: To measure variable volumes of liquids from 0 to 50 cm3 e.g. 16.7 cm3; to the nearest 0.05 cm3 per reading or 0.1 cm3 per sample taken, since determining the volume of liquid used requires two readings to be taken and subtracted one from the other.
• Measuring cylinder: To measure various volumes of liquids, accuracy depending on size and graduation of the cylinder (rather inaccurate).
• Beaker: To measure only approximate volumes of liquids, not to be used for precise quantities. It can be also used as a container.
• Conical flask: Used as a container.
• Evaporating dish: Used in crystallization.
• Volumetric flask: To prepare solutions with a specific volume, e.g. 250 cm3, 1000 cm3, etc., to the nearest 0.10 cm3.
• Test tube: Used for small-scale experiments.
• Boiling tube: To boil small quantities of solutions (this apparatus is very similar to the test tube with the only difference that its glass is thicker).
• Separating funnel: To separate two immiscible liquids.
• Funnel: Used in filtration.
• Crucible tongs: To hold large hot chemical apparatus.
• Test tube holders: To hold test tubes while heating them.
• Thermometer: To measure the temperature.
• Wire Gauze: Allows uniform heat distribution when using a Bunsen burner.

 Q1 Name the apparatus you would use to:

a. measure 25.6 cm3 of liquid.     

            Choose...

•             Pipette
•             Measuring cylinder
•             Burette

        

b. measure 15 cm3 of liquid as accurately as possible.     

            Choose...

•             Pipette
•             Measuring cylinder
•             Burette

        

c. measure approximately 100 cm3 of liquid.     

            Choose...

•             Pipette
•             Measuring cylinder
•             Burette

        

answer :

a. measure 25.6 cm3 of liquid.      = Burette b. measure 15 cm3 of liquid as accurately as possible.      = Pipette c. measure approximately 100 cm3 of liquid.      = Measuring cylinder

 Q2 Arrange the following pieces of apparatus in the order of greatest accuracy first:

Measuring cylinder

          

        

Beaker

             

        

Burette

             

        

Pipette

            

        

1.2.2 Drawing chemical apparatus

When we draw chemical apparatus we usually show only cross sections. Do not attempt to draw three-dimensional diagrams or shade the drawings. It is important that diagrams are neat and tidy, that the pieces of apparatus are in proportion to one another and that everything is clearly labeled. The diagrams should be large enough to be seen clearly and should be in pencil. Use a ruler for straight lines and keep a set of coins for drawing circles.

Below is some of the apparatus we will be using in grade ten. You should be able to draw, label and identify each piece of apparatus and know its function.

 Q3 Name the following glass articles which are usually found in a laboratory.

            Choose...

•             Pipette
•             Funnel
•             Conical flask
•             Beaker

        

            Choose...

•             Pipette
•             Funnel
•             Conical flask
•             Beaker

        

            Choose...

•             Pipette
•             Funnel
•             Conical flask
•             Beaker

        

            Choose...

•             Pipette
•             Funnel
•             Conical flask
•             Beaker

        

Steps to follow for lighting a burner

Before using the Bunsen burners in the lab, the teacher will open the main safety valve which would allow gas to come into the pipes (normally this will be closed)

a) Place the Bunsen burner on a porcelain tile to protect the surface of the bench.

b) Make sure that the Bunsen burner is attached to a gas tap.

c) Make sure that the air hole(s) of the Bunsen burner is/are closed.

d) Hold a lighted match or splint to the muzzle of the Bunsen burner and slowly open the gas tap until the gas ignites (Do not open the gas tap first, and keep your face and hair away from the burner). This will produce a very sooty, yellow flame.

e) Slightly open the air holes until the flame is blue at the bottom and slightly yellow at the top (the teacher will demonstrate first).

f) If a very hot flame is required, fully open the air hole and the gas tap. Be very careful with this type of flame and never leave the Bunsen burner with a blue flame when not

Why should you never leave the Bunsen burner with a blue flame when not in use?

There are two reasons for the last rule. First, a flame yellow at the top is more easily seen than a faint blue flame. Secondly, a blue flame is more likely to go off, allowing unburned gas to flow into the laboratory, which is not only a health hazard, but may cause an explosion.

Remember the following safety rules when using a Bunsen burner:

a) Do not open the gas tap before you place the lighted match near the muzzle of the burner.

b) Never leave the Bunsen burner with a blue flame when not in use.

Q4 Fill in the blank.

You should not open the tab before lighting a match to avoid any _______ in the laboratory.

Q5 Fill in the blank.

Never leave the Bunsen burner with a  flame, when not in use.

Q6 Fill in the blank.

A blue flame is less visible and more likely to go off than a

flame.

1.2.4 Heating a test-tube

Observe the following rules when heating a test-tube:

1. Never have the test-tube more than half filled with liquid, otherwise the liquid may boil and spill out, causing bodily harm or putting out the flame.

2. Always use test-tube holders and never tongs or your hand. Tongs may cause the tube to slip out or break.

3. Do not hold the test tube upright in the flame, instead have it inclined at an angle as shown below. An upright tube is more likely to spit the liquid out when the liquid inside it starts to boil.

4. Keep the test-tube moving as it is being heated, by moving your wrist from side to side. This will help to prevent ‘bumping’ due to the liquid overheating at one specific spot (local overheating).

5. When the liquid starts to boil vigorously remove the tube temporarily out of the flame, or reduce the flame, so the liquid will not spill out.

Q7 Which of the following should be done while heating a test-tube?

Always use test-tube holders.

When the liquid starts to boil vigorously, keep the tube for a while on the flame.

Keep the test-tube still as it is being heated.

Never have the test-tube more than half filled with liquid.

Always hold the test tube upright in the flame for maximum heating.

1.2.5 Heating a beaker or evaporating Dish

Rules for heating a beaker or an evaporating dish:

a) The beaker or dish must be placed on a tripod and gauze as shown below.

b) Do not more than half-fill the beaker or dish with liquid.

c) Use tongs and never your hands to transfer the hot evaporating dish to a steam bath.

1.2.6 Crystallization

Crystallization is the process of forming crystals. Crystals are solid “objects” with distinctive plane faces at specific angles with respect to each other, angles that are characteristic of the crystalline material. Your teacher will show you a few samples of crystals.

Q8 Fill in the blank.

 are solid "objects" with distinctive plane faces at specific angles with respect to each other, angles that are characteristic of the crystalline material.

Q9 Fill in the blank.

 is the process of forming crystals.

1.2.6 Crystallization – Cont.

Crystallization can take place by cooling a pure liquid, as in the case of ice crystals forming when pure water is cooled. It can also take place by heating a solution (e.g. sea water) until the liquid evaporates and solid salt crystals remain. It can also take place by evaporation. When sugar is dissolved in water, and the water is allowed to evaporate, sugar crystals appear. Sea salt is obtained from the sea by collecting sea water in flat beds and allowing the warmth of the sun to evaporate the water.

In order to obtain crystals, the solvent (the liquid in which a solid is dissolved) has to be carefully evaporated in the final stages.

The technique involves the following steps:

a) Heat the evaporating dish directly with the Bunsen burner until most of the water has evaporated. Do not boil dry.

b) Now, using tongs, transfer the evaporating basin to a steam bath as shown below crystals?

Note: If only a small volume of salt solution is to be evaporated (25cm3 or less) then step (a) can be omitted.

Home experiment: In order to obtain good, larger crystals of a salt or sugar, dissolve sugar or table salt in some water, until no more can dissolve. Filter the solution by pouring it through two layers of kitchen paper (see filtration later in this chapter). Place the solution in a clean glass, covered with a light sheet of paper. Wait a few days. Bring the crystal to school. Who has managed to obtain the largest crystals?

Q 10What are the two conditions that should be taken into consideration while performing a crystallization to obtain large crystals of salt?

the solution must be mixed with another solvent

the solution should be saturated

the crystallization should take place very slowly

the solution must be heated quickly at very high temperature

Q11 Which of the following are procedures used for obtaining crystals?

• cooling a pure liquid
• 
  
• evaporation
• 
  
• heating a solution
• 
  
• condensation

1.2.7 Units of volume in the laboratory

As you will soon see, many of the instruments we use in the laboratory are used to measure volume. In the laboratory, volume is usually measured in liters or in milliliters. The units that are used can be any of the following

Fill in the blank.

The units of volume used in the laboratory are  and milliliters.

answer 

1 liter=1 l=1 L=1000 mL=1000 cm3=1 dm3$\boxed{{\displaystyle \mathrm{}\mathrm{}\mathrm{}\mathrm{}\mathrm{}{}^{\mathrm{}}\mathrm{}{}^{}}}$

Fill in the blank.

The units of volume used in the laboratory are

and milliliters.

1.2.8 Using a measuring cylinder

A measuring cylinder is used to measure volumes of liquids where great accuracy is not important.

Measuring cylinders come in various sizes and it is important  to use the most appropriate 

cylinder for the volume to be measured e.g. if 10.0cm3 ± 0.5 ml of liquid is required,

then either a 10ml or 25ml cylinder should be used and not a 250ml cylinder.

If we want to measure 30 ml of water using a measuring cylinder, which of the following measuring cylinders 

would be most suitable?

250 ml measuring cylinder

50 ml measuring cylinder

25 ml measuring cylinder

100 ml measuring cylinder

1.2.8 Using a measuring cylinder – Cont.

When reading a measuring cylinder you must:

a) stand the cylinder on the bench, do not hold it in your hand.

b) bend down so that your eye is on the same level as the surface of the liquid when you read the scale.

c) measure to the bottom of the curved surface of the liquid. This curved surface is called a meniscus.

For very accurate measurements of volume (with an uncertainty between ± 0.05 cm3 and 0.1cm3), 

pipettes and burettes must be used (explained later).

Next

1.2.9 Filtration

Filtration is the process of separating a liquid from an insoluble solid (i.e. does not dissolve in the liquid). A beaker, filter stand, filter funnel and a piece of filter paper are required.

Name the chemical technique that can be used:

To separate salt from a solution of sea water: 

Name the chemical technique that can be used:

In a sewage works, to remove insoluble material from water: 

1.2.9 Filtration – Cont.

It is important to fold the filter paper properly and this is done as follows:

a) Fold the filter paper in half and then into quarters.

b) Open the paper out to make a cone with a thickness of three on one side and one on the other.

The filter paper now fits neatly into the filter funnel. Wet the filter paper before starting the filtration and always pour liquid onto the three-thickness side and never allow liquid to come within 1cm of the top of the paper.

Never poke a wet filter paper with your finger, a spatula or a glass rod as this may tear the paper and you will have to start again.

How do you fold a filter paper to fit it in a funnel?

Open the paper out to make a cone with equal thickness on each side.

Wet the paper with distilled water then fold it into half.

Open the paper out to make a cone with a thickness of three on one side and one on the other.

Fold the filter paper in half and then into quarters.

The liquid, which comes through the filter paper, is known as the filtrate and the solid, is left behind on the paper, 

is called the residue.

Fill in the blanks.

is the process of separating a liquid from an insoluble solid.

Fill in the blanks.

The

is the liquid which comes through the filter paper.

1.2.10 Measuring mass

The Electric Balance

In earlier courses you have learned how to use a beam balance to measure to the nearest 0.1 g. 

Now, you have to be able to measure to the nearest 0.01 g. To do this, you will need to use an electric balance. 

Your teacher will demonstrate its use.

Weighing by Difference

When measuring a mass, either using the ‘dial-O-gram’ or the electronic scale, it is always more accurate to

 weigh by difference whenever possible.

Suppose you would like to measure about of 1g of a solid X. Do the following:

a) Weigh accurately and record the mass of a weighing bottle (m1).

b) Add approximately 1g of a solid to the bottle and accurately record the mass (m2).

c) The accurate mass of the solid is obtained by subtraction (m2 - m1).

This method reduces the effect of any mechanical error that may be present in the balance.

1.2.11 Using a pipette

A pipette is designed to measure a specified fixed volume of liquid when correctly filled, 

usually to the nearest 0.05 cm3. In other words you can only select one of a specified number of volumes, not in between.

 The common capacities of pipettes are 5 ml, 10 ml, 25 ml and 50 ml.

Never use your mouth to suck liquid into a pipette. Instead, use a pipette filler. 

A pipette filler has three valves, marked either A, S and E or 1, 2 and 3.

a) Attach the filler to the pipette.

b) Squeeze valve A (for air out) (valve 1) and at the same time squeeze the bulb of the filler. 

This drives the air out of the filler.

c) Place the pipette in the liquid to be used.

d) Squeeze valve S (for suck) (valve 2) and the liquid is sucked into the pipette. 

Continue until the liquid is a few centimeters above the calibration mark.

e) Move your eyes to the same level as the calibration mark and carefully squeeze valve E (for empty) 

(valve 3) to empty some liquid until the bottom of the liquid meniscus just touches the calibration mark. 

(If you overshoot then you must go back and repeat steps ‘d’ and ‘e’)

f ) Remove the filler from the pipette and allow the liquid to run out into a clean beaker or flask.

g) After the liquid has run out, touch the bottom of the pipette against the side of the beaker or flask.

 A little liquid should still be left in the tip of the pipette. 

Do not blow out this liquid into the beaker or flask as the measurement requires this liquid to be left over.

Q

A specified fixed volume of liquid in volumetric pipettes means

an exact volume such 26.5 ml

a volume with uncertainty of + or - 1 ml

a non-variable volume

an exact volume

A specified fixed volume of liquid in volumetric pipettes means

a non-variable volume

an exact volume

a volume with uncertainty of + or - 1 ml

an exact volume such 26.5 ml

You are required to measure out 25 cm3 of liquid as accurately as you can.

The most suitable glassware used to carry on this measurement is the

.

1.2.12 Using a burette

A burette is designed to measure unspecified volumes of liquid (between 0.0 ml and 50.0 ml). 

The commonest burette is graduated from 0.0 ml to 50.0 ml in 0.1 ml units, and it should be read to the nearest 0.05 ml.

It should be noted that one drop of liquid coming out of a burette, a pipette or a dropper has a volume very nearly

  equal to 0.05 ml. (How can this be determined?)

How to Fill a Burette

a) Place the burette in a burette stand and insert a filter funnel in the mouth of the burette.

b) Place some of the liquid to be measured into the burette.

c) Let out some liquid until no air is left in the section of the burette between the valve (tap) and the tip (outlet). I

f you can’t do that, ask for help from the teacher.

d) Pour in the liquid from a beaker until the liquid is close to the 0.0 mark (almost completely filling the burette).

e) Remove the funnel. If you have filled the burette over the zero mark, open the valve to allow some liquid to run out, 

until the bottom of the liquid meniscus is in line with 0.0 mark (remember to position your eyes at the same level as 

the 0.0 mark). The burette is now ready to be used.

It is good practice to place a white piece of paper behind the burette when taking the reading. 

The bottom of the meniscus is difficult to observe without a white background.

Fill in the blank.

The instrument used to measure a volume of 27.0 cm3 with an uncertainty of ± 0.1cm3 or less is  

 .

Fill in the blank.

In 1.0 ml of liquid there is  

 drops.

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