Chem

Question 0

Empirical formula

Answer 0

The simplest whole number ratio of atoms of each element in a compound.

Question 1

Molecular formula

Answer 1

Actual number of atoms of each element in a molecule

Question 2

General formula

Answer 2

The simplest algebraic formula for a member of a homologous series.

Question 3

Structural formula

Answer 3

The minimum detail that shows the arrangement of the atoms in a molecule

Question 4

Displayed formula

Answer 4

Shows the relative positioning of the atoms and the bonds between them

Question 5

Avogadro constant

Answer 5

The number of atoms in 12g of carbon 12.

6.022x10-23

Question 6

How can you reduce errors in measuring mass?

Answer 6

Use a more accurate balance

Larger mass

Weighing sample before and after addition and then calculating the difference will ensure a more accurate measurement of the mass added.

Question 7

What does it mean if the percentage error due to the apparatus is less than the percentage difference between the actual value and the calculated value?

Answer 7

There is a discrepancy in the result due to other errors

Question 8

If the percentage error due to the apparatus is greater than the percentage difference between the actual value and the calculated value?

Answer 8

There is no discrepancy and all errors in the results can be explained by the sensitivity of the equipment

Question 9

How can you decrease apparatus error?

Answer 9

Decrease the sensitivity error by using apparatus with a greater resolution.

Increase the size of the measurements made

Question 10

Cm^3 to Dm^3

Answer 10

Divide by 1000

Question 11

Cm^3 to m^3

Answer 11

Divide by 1,000,000

Question 12

Dm^3 to m^3

Answer 12

Divide by 1000

Question 13

How do you get concentration in gdm^-3

Answer 13

Concentration in mol dm^-3 x Mr of the substance

Question 14

Percentage yield

Answer 14

Actual yield/ theoretical yield

X100

Question 15

Percentage atom economy

Answer 15

Mass of useful products/mass of all reactants

X100

Question 16

Irritants

Answer 16

Dilute acid and alkalis

Must wear googles

Question 17

Corrosive

Answer 17

Stronger acids and alkalis

Wear googles

Question 18

Flammable

Answer 18

Keep away from naked flames

Question 19

Toxic

Answer 19

Wear gloves
Avoid skin contact
Wash hands after use

Question 20

Oxidising

Answer 20

Keep away from flammable/ easily oxidised materials

Question 21

Why should large amounts of zinc sulphate not be used?

Answer 21

Decomposition is likely to be incomplete

Question 22

Why does the crucible need to be dry?

Answer 22

A wet crucible would give an inaccurate result.

It would cause mass loss to be too large as water would be lost when heating.

Question 23

How does the lid improve the accuracy?

Answer 23

Prevents loss of solid from the crucible but should be loose fitting to allow gas to escape.

Question 24

Why should small amounts of solid not be used?

Answer 24

The errors in weighing are too high

Question 25

What is concentration in gdm^3 the same as?

Answer 25

The mass of the solute dissolved in 1dm^3

Question 26

When is a gas syringe usually used?

Answer 26

To work out moles of gas To follow reaction rates

Question 27

What should you do when recording volume?

Answer 27

Note down the temperature and pressure of the room

Question 28

What two things are important when drawing a diagram?

Answer 28

Don't leave gaps in the diagram where the gas could escape Draw the gas syringe with measurements on it

Question 29

Potential errors when using a gas syringe

Answer 29

Gas escapes before bung is inserted Syringe sticks Some gases like carbon dioxide and sulphur dioxide are soluble in water so the true amount of gas is not measured.

Question 30

Improving accuracy when weighing solutions?

Answer 30

Weighing bottle again after it has been emptied into the beaker. The weighing bottle could be washed and washings added to the beaker Fill so the bottom of the meniscus sits on the line on the neck of the flask

Question 31

Why is a white tile used underneath the flask?

Answer 31

To help observe the colour change.

Question 32

What precautions should you take if you are working with an unknown substance?

Answer 32

Treat the substance as potentially toxic and wear gloves.

Question 33

Why is a conical flask used in preference to a beaker?

Answer 33

It is easier to swirl the mixture in a conical flask without spilling the contents.

Question 34

How can distilled water be used in a titration?

Answer 34

It can be added to a conical flask during a titration to wash the sides of the flask so that all the acid on the side is washed into the reaction mixture to react with the alkali.

Question 35

Why does distilled water not affect the titration reading?

Answer 35

Water does not react with the reagents or change the number of moles of acid added.

Question 36

What can we say about the results if our data is concordant?

Answer 36

The results are accurate and reproducible and the titration technique is good/consistent.

Question 37

What is important to consider when titrating mixtures?

Answer 37

If the mixture contains other substances that have acid based properties.

Question 38

Why is it important to do titrations on several samples in quality control?

Answer 38

The amount/ concentration of the chemical being tested may vary between samples.

Question 39

Why is magnesium hydroxide suitable for dealing with excess stomach acid?

Answer 39

It has a low solubility in water and is only weakly alkaline so not corrosive or dangerous to drink. It does not produce any carbon dioxide gas.

Question 40

Relative atomic mass

Answer 40

The average mass of one atom compared to one twelfth the mass one atom of carbon 12

Question 41

How do you calculate percentage error?

Answer 41

Sensitivity error/ measurement made on apparatus | x by 100

Question 42

How do you calculate the maximum percentage error?

Answer 42

add all the individual equipment errors together

Question 43

How can you reduce errors in a titration?

Answer 43

Replacing measuring cylinders with pipettes or burettes which have lower apparatus sensitivity error will lower the error. To reduce the error in a burette reading it is necessary to make a titre a larger volume. This could be done by: increasing the volume and concentration of the substance in the conical flask or by decreasing the concentration of the substance in the burette. Fill the jet space prior to commencing the titration as it would lead to errors otherwise as it will fill during the titration. This will lead to a larger than expected titre reading.