Experimental Chemistry

Question 1

what apparatus is used for measuring fixed volumes
eg.20.0cm3 or 25.0cm3

Answer 1

pipette

long thingy with a small compartment in the middle? if that makes sense?

Question 2

what apparatus do you use to measure mass?

Answer 2

electronic balance

Question 3

what apparatus do you use to measure time?

Answer 3

stopwatch

Question 4

what apparatus do you use to measure temp.?

Answer 4

thermometer

Question 5

what apparatus do you use to measure approximate volumes of liquid?

Answer 5

beaker and measuring cylinder

Question 6

what apparatus is used to measure** exact amounts** of solution (9able to correct to 2dp? )
eg. 18.10cm3

Answer 6

Burette

Question 7

what apparatus is used for measuring gas?

Answer 7

Gas syringe

Question 8

How to collect insoluble gas?
examples of insoluble gas: hydrogen (H2), oxygen (O2), carbon dioxide (CO2)

Answer 8

By Displacement of water

https://digitalteachers.co.ug/wp-content/uploads/2020/01/downward-displacement-of-water.png

Question 9

How to collect gases that are denser than air? (and soluble in water?)

Mr of more than 28 = denser than air.
Examples: chlorine (Cl2), hydrogen chloride (HCl), carbon dioxide (CO2).

Answer 9

By downward delivery

https://tse3.mm.bing.net/th?id=OIP.nUcJvPpdR2Gp7ADAD28fRgHaC-&pid=Api&P=0&h=180

Question 10

How to collect gases that are less dense than air? (and soluble in water?)

Mr of less than 28 = less dense than air.
Examples: ammonia (NH3) and hydrogen (H2)

Answer 10

By Upward delivery

Question 11

How to dry a gas, absorb a gas

Answer 11

1) drying with concentrated Sulfuric Acid
2)Drying with Quicklime (calcium Oxide)
3) Drying with fused calcium chloride

Question 12

How to test for purity of a liquid?

Answer 12

1. Melting point & Boiling point determination. A pure substance has fixed melting and boiling points
   eg. Water melting point =0 °C, Boiling point = 100°C
2. Chromatography
   A pure substance will produce only one spot on the chromatogram.

Take note that:
 impurities lower the melting point & increase the boiling point of a substance
 an impure substance will melt or boil over a range of temperature (eg. 55°C to 70°C)
 an impure substance will produce more than one spot on the chromatogram

Question 13

When do you use filtration?

Answer 13

to separate an insoluble solid from a liquid.
Residue: insoluble solid remaining on filter paper
Filtrate: Liquid passed through filter paper

Question 14

Describe the experiment using filtration

Answer 14

1. Add water to the mixture of sand & salt
2. Stir to dissolve salt
3. Filter the mixture. Residue is sand; filtrate is salt
   solution
4. To obtain salt: heat the filtrate to obtain saturated
   solution
5. Cool to allow crystals to form
6. Dry between pieces of filter paper.

Question 15

Describe experiment using Crystallisation

Answer 15

1. Add water to dissolve the impure copper(II) sulfate solution
2. Filter to remove impurities
3. Heat the filtrate to obtain saturated solution
4. Cool to allow crystals to form
5. Dry crystals between pieces of filter paper.

Question 16

When is Crystalisation used?

Answer 16

Separate a soluble solid from its solution
Eg. copper(II) sulfate from copper(II) sulfate
solution

Question 17

When is Distillation used?

Answer 17

To separate a liquid from a solution
Eg. Obtain water from salt solution

https://images.app.goo.gl/VxrBRDjkrjsSXURV6

Question 18

Describe experiment using distillation

Answer 18

(1) The bulb of the thermometer should be
positioned beside the side arm of the
distillation flask to measure boiling point of
the vapour
(2) The condenser should be positioned so that it
slants downwards to allow the condensed
liquid to flow into the conical flask.
(3) Boiling chips are added to ensure smooth
boiling.
(4) The condenser cools the vapour back to a
liquid.
(5) If a volatile distillate is to be collected, use a
water bath for heating to prevent the
solution from catching fire.
(6) Beaker of ice placed under the distillate
collected to cool the vapour and form liquid

Question 19

When is Fractional Distillation used?

Answer 19

Used to separate two or more miscible liquids
with different boiling points. Miscible liquids are liquids that dissolve in each other.

Liquid mixture is boiled to vaporise the liquids
according to its boiling point. Liquid with the lowest boiling point will be collected first.

Question 20

Describe how industries use Fractional Distillation

Answer 20

To obtain fractions of liquid air
eg. Obtain oxygen from air
Separate crude oil into different fractions

Question 21

What is Paper Chromatography used for?

Answer 21

(a) separate the components of dyes in a mixture
(b) identify the dyes present in a mixture
(c) determine if a substance is pure
(if there is only one spot on the chromatogram, the
substance is pure)

most soluble dye would travel the furthest distance

Question 22

Why should the starting line should be drawn with a pencil rather than with ink. (paper chromatography)

Answer 22

Ink contains dyes and will interfere with the
results of the chromatogram.

Question 23

Why must the start line must be drawn be above the solvent level? (paper chromatography)

Answer 23

To prevent the dyes from dissolving into the solvent.

Question 24

How to calculate Rf
(paper chromatography)

Rf means: relative distance the spot traveled compared to the distance it could have traveled if it moved with the solvent front

Answer 24

Rf = distance travelled by the spot
———————————————–
distance travelled by the solvent
Rf value has NO units

line in the middle means divide

Question 25

Why should the spots of solutions and dyes on the starting line be small? (paper chromatography)

Answer 25

So as to avoid smudging and overlapping of neighbouring spots.

Question 26

Why is it necessary to close the container by a
lid? (paper chromatography)

Answer 26

Prevent solvent evaporation

Question 27

Define Element

Answer 27

It is a pure substance that** cannot be broken down** into two or more simpler substances by chemical processes.

Eg. ALL elements in the Periodic Table

Question 28

Define Compound

Answer 28

A compound is a pure substance that contains** two or more elements** that are** chemically combined **in a fixed ratio.

Eg
H2O = 2 hydrogen & 1
oxygen atoms
NaCl = 1 sodium & 1
chlorine atom

Question 29

Define Mixture

Answer 29

Mixtures are made up of two or more substances that are not chemically combined.

Eg
* Petrol (contains a mixture of
carbon compounds)
* Air (is made up of nitrogen
gas, N2, oxygen gas, O2,
Carbon dioxide gas CO2)

Question 30

How to seperate a mixture?

Answer 30

The components of a mixture can be
separated by physical processes
eg.
1. magnetic separation
2. filtration
3. crystallization
4. fractional distillation
5. chromatography
6. distillation

Question 31

How to seperate a compound?

Answer 31

A compound can only be broken down into its
elements or into simpler compounds by
chemical processes eg.
1. thermal decomposition:
- heating calcium carbonate to obtain
calcium oxide and carbon dioxide
2. electrolysis
- melting sodium chloride at high
temperature to obtain sodium metal and
chlorine gas

Question 32

What are the properties of a mixture?

Answer 32

It does not have a fixed melting & boiling
point (melts or boils over a range of
temperatures eg: from 200C to 350C)

Question 33

What are the properties of a compound?

Answer 33

The physical and chemical properties of a
compound are different from those of its
constituent elements.

[Compound Fixed Melting point]
>Calcium carbonate 825
>Calcium oxide 2 572
>Carbon dioxide -56.6

Question 34

Energy changes when a mixture is formed?

Answer 34

No chemical reaction takes place when a
mixture is formed — usually there is little or no
energy change.

Question 35

Energy changes when a compound is formed?

Answer 35

A chemical reaction takes place when a
compound is formed — usually there is an
energy change,
e.g. the reactants get hot or cold.