1. Solids

Never return unused chemicals to the reagent bottle

From reagent bottle Use a clean and dry spatula or spoon

Place the stopper upside down on the bench.

Mouths of test-tube and reagent bottle are at the eye level.

Never return unused chemicals to the reagent bottle

(a) Pouring a liquid from a reagent bottle to a test tube

Mouths of test-tube and beaker are at the eye level

Pour the liquid along the spout of the beaker.

spout of the beaker

Use gas generator

It can produce a large amount of gas

easily control the flow of the product gas

What are the advantages of using tap funnel?

Rate of addition of liquid can be controlledPrevent the gas escaping from the funnel

re ac tin g liq u id

re ac tin g so lid

ro u n d b o tto m ed fla sk

g a s o u t

ta p fu n n e l

For gases that do not dissolve in water

1. Displacement of water

It a gas is produced from a hot vessel and heating is stopped, water may be sucked back to the hot vessel is

Sucking back

g as

w a te r

W a te r is b e in g su ck ed b ack

How to prevent sucking back?The delivery tube must be removed from water before heating is stopped.

g as

w a te r

W a te r is b e in g su ck ed b ack

> (i) upward delivery (downward displacement)

> (ii) downward delivery (upward displacement)

For gases having densities much smaller than air. Examples:

hydrogen, ammonia

Up w a rd d e live ry

g a s

For gases having densities much larger than air. Examples:

carbon dioxide, chlorine

D ow nw ard de live ry

G a s

For collecting all kinds of gases

Can be used to measure volume of the gasPrecaution

•Horizontal position

•Prevent the plunger from falling out

•Keep the syringe clean, dry and free from grease.

Two uses:

Draw a labelled diagram for preparation of gas

Use of Bunsen Burner

Bunsen flame

Heating liquids

Construction of a Bunsen burner

a ir h o le

to w ng asb ase

je tco lla r

b a rre l

•Close the air hole.

•Put a lighted match near the top of barrel.

•Turn on the gas supply

How to light a Bunsen burner?

air hole

towngasbas

e

jetcollar

barrel

How to control the size of a Bunsen flame?

by using the gas tap

When there is no immediate use of a burner, what should you do?

Turn it off; orleave it with a small luminous flame.

Turn the collar to adjust the size of the air-hole

Non-luminous flame

Luminous flame

Small air-hole

Large air-hole

or air hole is closed

The air hole is closed completely

There are 3 zones.

Non-luminous zoneLuminous zoneDark zone

Non-luminous zone

Luminous zone

Dark zone

This flame is not very hot.

The air hole is open.

There are 3 zones.

Non-luminous zoneGreen-blue zone

Dark zone

Non-luminous zone

Green-blue zone

Dark zone

This flame is hotter than luminous flame.

•The amount of air getting into the barrel is too much.

•The gas supply is too low.

How do you know that there is ‘striking back’?

Why does striking back occur?

What is ‘striking back’?

A high pitched sound will usually be heard.

Gas burns at the jet instead of the mouth of the barrel.

What should you do?

Caution!

The collar is very hot.

Turn off the gas supply immediately.

shake the tube

Use a small non-luminous flame

How to get uniform heating?

Use test-tube holder

Heat the upper part of the liquid first

move the tube around the flame

The tube should not be more than 1/3 full.

Safety precaution

The tube should be pointed to open area, never to anybody

For larger amount of liquidA wire gauze is placed between the beaker and the flame

The beaker should not be filled more than 1/2 full.

The liquid is heated indirectly

Inflammable liquids may easily catch fire.

Why are inflammable liquids heated indirectly?

Oil bath may be used to achieve a higher temperature.