Topic 5-Formulae, Equations & Amounts of Substances

Question 1

Give the definition of the Empirical Formula

Answer 1

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

Question 2

If you have 5cm, how many dm will you have?

Answer 2

0.005dm

Question 3

What does Avogadro’s constant tell you? What is the figure?

Answer 3

The number of particles in a mole, 6.02 x 10^23

Question 4

Give the definition for the molecular formula.

Answer 4

The molecular formula gives the actual numbers of atoms of each type of element in a molecule.

Question 5

What is a base?

Answer 5

Bases are substances that act as the opposite of acids, they also release hydroxide ions in aqueous solutions.

Question 6

A solution of sodium hydroxide is described as having a concentration of 0.4 mol dm-3. Explain what this means.

Answer 6

0.4 mols of sodium hydroxide are dissolved in every dm3 of solution.

Question 7

What number must you add to the degrees in C to get the degrees in Kelvin?

Answer 7

273

Question 8

What equation can you use for % uncertainty?

Answer 8

(uncertainty/measurement) x 100 x no.of measurements

Question 9

What will form when a reactive metal + acid react?

Answer 9

Salt + Hydrogen

Question 10

What will form when you react an acid and a base?

Answer 10

Salt + water

Question 11

What reactants will produce salt + water + carbon dioxide?

Answer 11

Acid + carbonate

Question 12

Define the concentration of a solution.

Answer 12

How many moles/grams are dissolved per 1dm”3

Question 13

What are the units for concentration?

Answer 13

g dm-3
or
mol dm-3

Question 14

What type of reaction has taken place if two aqueous solutions react to form a solid?

Answer 14

A precipitation reaction i.e solid precipitate has formed.

Question 15

What is the only thing ionic equations show?

Answer 15

Only the reacting particles (and products they form)

Question 16

Define Molar gas volume.

Answer 16

The space one mole of gas occupies at a certain temp and pressure.

Question 17

What is the volume of 1 mol of gas at room temperature and pressure?

Answer 17

24dm”3 mol-1

Question 18

What is the volume of 1 mol of gas at standard temperature and pressure?

Answer 18

22.4dm”3 mol-1

Question 19

What is the IDEAL gas equation?

Answer 19

PV=nRT

Question 20

What is a hazard?

Answer 20

Anything that has the potential to cause harm or damage.

Question 21

What is risk?

Answer 21

The probability of someone or something being harmed if they are exposed to the hazard

Question 22

Define systematic error

Answer 22

These errors are the same every time you repeat the experiment e.g. set up of equipment.

Question 23

Define a random error

Answer 23

These errors are different every time you repeat the experiment e.g. error reading burette.

Question 24

Which type of error can be reduced by repeating the experiment?

Answer 24

The random errors.

Question 25

If the conical flask is washed out between each titrations, will this effect the moles?

Answer 25

No this has NO EFFECT on mols.

Question 26

How will the experiment be affected if the pipette is washed out with water before each titration?

Answer 26

It will dilute what is in the conical flask so titres will be smaller.

Question 27

What effect will completely filling the volumetric flask rather than it only being to the graduation line, have?

Answer 27

Solution in the burette will be too dilute therefore titre will be larger than it should be.

Question 28

How do you know what is ionic? | which ions become disassociated

Answer 28

Roughly- Metal (or ammonium) compounds. Acids in solution = ionic (only split up ions if it's aqueous) anything else e.g. insoluble salts. = not ionic

Question 29

How do ionic equations for acids and metal hydroxides differ?

Answer 29

All ions disassociate so in the end its always a reaction between H + OH --> H2O

Question 30

What happens in ionic equations for the reaction between acids and metal carbonates?

Answer 30

It will ALWAYS be | CO3 + 2H ----> CO2 + H2O

Question 31

Even in net ionic equations, only which type of element should have a charge?

Answer 31

AQUEUOUS atoms are only ever written with a charge. | Leave gases and solids neutral!!!

Question 32

What should you do with the conical flask to ensure the results of the experiment aren't affected

Answer 32

rinse with distilled or deionised water.

Question 33

Equation for atom economy?

Answer 33

mass of atoms in desired product/ | mass in all reactants x100

Question 34

Equation for percentage yield?

Answer 34

actual yield/ maximum theoretical yield x 100

Question 35

Define "mole"

Answer 35

One mole is the amount of substance that contains the same number of particles as the number of carbon atoms in 12g of C12.

Question 36

What can you know about an equation involving a basic oxide?

Answer 36

That a basic oxide acts oppositely to an acid

Question 37

When are your results labelled as "concordant"

Answer 37

When they are within 0.1 of each other (NOT INCLUDING ROUGH TITRE)

Question 38

In a question you know that two compounds are in a 1:1 ratio. How do you work out the percentage yield of the compound?

Answer 38

As it is in 1:1 ratio, this mean that the THEORETICAL YIELD is equal to this number of mols. Then rearrange the equation.

Question 39

Define the term 'mole'

Answer 39

One mole is amount of substance that contains that contains the same number of particles as the number of carbon atoms in exactly 12g of carbon 12

Question 40

What are the units for molar mass?

Answer 40

g mol-1 | LITERALLY MR THINK G / MOL

Question 41

Explain 3 actions the technician might take in the procedure just before the end point of titration to ensure end point accurate

Answer 41

- White tile to accurately see point of colour change - Drop by drop when closer to rough titre TO AVOID OVERSHOOTING - swirl to ensure all alkali and acid react.

Question 42

In a question where they use a 100cm3 solution and then only put 10cm3 into conical flask remember.....

Answer 42

To divide the moles by 10! | 10/100 of solution so not representational of just 10!

Question 43

How does a graph show direct proportion?

Answer 43

Straight line through origin.

Question 44

Why would you add a pinch of Xcarbonate to acid before the reaction

Answer 44

To saturate solution with CO2.

Question 45

What happens to a solution during a dilution?

Answer 45

Will increase the volume, and decrease the concentration but the moles will stay the same.

Question 46

What is 1000 mg in g?

Answer 46

1g = 1000mg

Question 47

How many kg in 1 tonne?

Answer 47

1000kg