Chapter 2 - Measurment and Purity

Question 1

When measuring where do put the decimal points to.

Answer 1

The 1st or 2nd decimal point

Question 2

Are mercury thermometers or digital thermometers more accurate

Answer 2

Digital thermometers are.

Question 3

In terms of mass what is used more for chemistry

Answer 3

Grams are used more than kilograms.

Question 4

In measuring when do mostly use the measuring cylinder

Answer 4

When measuring volumes of liquids where accuracy isn’t an important factor

Question 5

What is the apparatus pipette used for

Answer 5

Pipettes are the most accurate way of measuring the fixed volume of liquids.

Question 6

What is the apparatus Burette used for

Answer 6

It’s most accurate way of measuring a variable volume of liquid.
E.g titration

Question 7

What apparatus is most used for measuring gas

Answer 7

The volume of a gas sometimes needs to be measured and is done by collecting it in a graduated measuring apparatus
A gas syringe is usually the apparatus used.

Question 8

What is a graduated cylinder inverted in water used for

Answer 8

When measuring a gas a graduated cylinder inverted in water, provided the gas isn’t water-soluble can be used to measure gas.

Question 9

When is the appropriate time to flip the cylinder upright

when measuring gas.

Answer 9

If the gas happens to be heavier than air and is colored, the cylinder can be used upright.

Question 10

What is paper chromatography

Answer 10

This technique is used to separate substances that have different solubilities in a given solvent (e.g. different coloured inks that have been mixed to make black ink)

Question 11

What are steps for paper chromotography

Answer 11

A pencil line is drawn on chromatography paper and spots of the sample are placed on it. Pencil is used for this as ink would run into the chromatogram along with the samples.
The paper is then lowered into the solvent container, making sure that the pencil line sits above the level of the solvent so the samples don´t wash into the solvent container
The solvent travels up the paper by capillary action, taking some of the coloured substances with it
Different substances have different solubilities so will travel at different rates, causing the substances to spread apart. Those substances with higher solubility will travel further than the others
This will show the different components of the ink / dye

Question 12

What is the simplified steps of chromatography

Answer 12

1. First set up the chromatography experiment
2. Secondly lower paper into beaker with appropriate solvent and wait for solvent to travel up the paper.
3. Lastly analyse chromatogram to see the different components of ink/dye

Question 13

What happens if you use an impure substance in chromatography

Answer 13

An impure substance will show up with more than one spot, a pure substance should only show up with one spot

Question 14

If a substance used is a mixture in chromatography what happens

Answer 14

If the substance is a mixture, it will separate on the paper to show all the different components as separate spots

Question 15

If two substance that are identical are used in chromatography what will happen

Answer 15

If two or more substances are the same, they will produce identical chromatograms

Question 16

What’s the difference between paper chromatography and chromatogram

Answer 16

Paper chromatography is the name given to the overall separation technique while a chromatogram is the name given to the visual outcome of

Question 17

What do pure substances melt and boil at

Answer 17

Pure substances melt and boil at specific and sharp temperatures. Eg water has a boiling point of 100°C and a melting point of 0°C

Question 18

What is range of melting and boiling for mixtures

Answer 18

Mixtures have a range of melting and boiling points as they consist of different substances that melt or boil at different temperatures. Therefore the melting points and boiling points of substances can be used to check whether something is a pure substance or is mixture.

Question 19

What is a pure substance

Answer 19

A pure substance consists of only one substance and contains nothing else.

Question 20

In food and drugs why is having a pure substance important

Answer 20

as impurities could be dangerous even in small amounts

Question 21

What are Melting and boiling points used for for with food and drugs

Answer 21

It’s used to assess the purity of food and drugs

Question 22

If something is impure what will happen e.g water

Answer 22

For example, if a sample of water melts at exactly 0°C and boils at exactly 100°C then the water is pure, but If the melting and boiling points of the water aren’t these exact values then the water must be impure and contain other substances i.e. it must be a mixture

Question 23

What are retention factor values

Answer 23

These values are used to identify the components of mixtures

Question 24

What does calculating the retention factor value (Rf) do

Answer 24

Calculating the Rf value allows chemists to identify unknown substances because it can be compared with Rf values of known substances under the same conditions. The Rf value of a particular compound is always the same

Question 25

How do you calculate retention factor value (Rf)

Answer 25

Retention factor = distance moved by compound ÷ distance moved by solvent
The Rf value is a ratio and therefore has no units
It’s kinda like chromatography.

Question 26

What are locating agents

Answer 26

For chromatography to be useful the chemist needs to be able to see the components move up the paper, which is not the case for invisible samples such as proteins
Locating agents are substances which react with the sample and produce a coloured product which is then visible

Question 27

When is the chromatogram treated with locating agent

Answer 27

The chromatogram is treated with the agent after the chromatography run has been carried out, making the sample runs visible to the naked eye

Question 28

How do you seperate a mixture of solids

Answer 28

For a difference in solubility, a suitable solvent must be chosen to ensure the desired substance only dissolves in it and not other substances or impurities

Question 29

What are immiscible liquids

Answer 29

They are liquid solutions that do not dissolve in one another. They are liquids that do not mix in equal proportions.

Question 30

How can immiscible liquids be separated

Answer 30

Immiscible liquids can be separated using a separating funnel or by decanting

Question 31

What is decanting

Answer 31

It’s gradually pouring out a liquid from another liquid.

Question 32

What’s filtration

Answer 32

Used to separate an undissolved solid from a mixture of the solid and a liquid / solution ( e.g. sand from a mixture of sand and water). Centrifugation can also be used for this mixture. Pouring insoluble mixture of solid and liquid in the filter tunnel Using the filter the liquid particles will gradually fall through and sold particles will not

Question 33

What’s residue in filtration

Answer 33

The solid particles that can’t get through the filter paper

Question 34

What’s filtrate in filtration

Answer 34

It’s the liquid particles that pass through the filtrate

Question 35

What’s crystallisation

Answer 35

Used to separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold (e.g. copper sulphate from a solution of copper (II) sulphate in water)

Question 36

How does crystallisation work

Answer 36

The solution is heated, allowing the solvent to evaporate to leave a saturated solution behind.
Test if the solution is saturated by dipping a clean, dry, cold glass rod into the solution. If the solution is saturated, crystals will form on the glass rod

Question 37

What’s simple distillation

Answer 37

Used to separate a liquid and soluble solid from a solution (e.g. water from a solution of saltwater) or a pure liquid from a mixture of liquids

Question 38

How does simple distillation work

Answer 38

The solution is heated and pure water evaporates producing a vapour which rises through the neck of the round-bottomed flask
The vapour passes through the condenser, where it cools and condenses, turning into pure liquid H2O which is collected in a beaker
After all the water is evaporated from the solution, only the solid solute will be left behind

Question 39

What is fractional distillation

Answer 39

Used to separate two or more liquids that are miscible with one another (e.g. ethanol and water from a mixture of the two)

Question 40

How does fractional distillation work

Answer 40

The solution is heated to the temperature of the substance with the lowest boiling point
This substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker
All of the substance is evaporated and collected, leaving behind the other components(s) of the mixture

Question 41

What does miscible mean

Answer 41

Miscible means liquids that can be mixed together in all proportions