Amount of Substance

Question 1

What is the definition of relative atomic mass?

Answer 1

The average mass of an atom of an element relative to 1/12th of the relative atomic mass of an atom of carbon-12

Question 2

What is the definition of relative formula mass?

Answer 2

The average mass of that molecule compared to 1/12th of the relative atomic mass of carbon-12

Question 3

What is avogrado’s constant?

Answer 3

6.022 × 10²³

Question 4

What is the equation for moles using mass and Mr?

Answer 4

moles = mass / Mr

Question 5

What is molar mass and what are the units?

Answer 5

1 mole of atoms, it is numerically the same as Mr. The units are g/mol or g mol^-1

Question 6

How do you work out the number of molecules?

Answer 6

moles x avogadro’s constant

Question 7

How do you work out the number of atoms?

Answer 7

moles x avogadro’s constant x number of atoms

Question 8

What is the equation for % uncertainty?

Answer 8

instrument uncertainty / quantity measured x 100

Question 9

How do you convert g/dm3 into mol/dm3

Answer 9

÷ Mr

Question 10

What is the equation to find the dilution factor?

Answer 10

initial concentration / target concentration

Question 11

What is the dilution factor?

Answer 11

The sum of parts

Question 12

How do you find the volume of 1 part in the dilutions method?

Answer 12

volume of solution / dilution factor

Question 13

What is the ideal gas equation?

Answer 13

PV=nRT

Question 14

How do you convert Celsius into Kelvin?

Answer 14

+273

Question 15

How do you convert Kelvin into Celsius?

Answer 15

-273

Question 16

How do you convert kPa into Pa?

Answer 16

x 10^3

Question 17

How do you convert mPa into Pa?

Answer 17

x 10^6

Question 18

How do you convert cm³ into m^3?

Answer 18

x 10^-6

Question 19

How do you convert dm^3 into m^3?

Answer 19

x 10^-3

Question 20

What are the two steps of finding the Mr of a gas?

Answer 20

Find the moles with the ideal gas equation of n=PV/RT
Find the Mr with the equation Mr=mass/mol

Question 21

What are the errors in calculating the Mr?

Answer 21

The volume of gas in a syringe is greater than the true volume because some air leaked into the syringe, so the Mr is too small.
The volume of the gas in the syringe is less than the true volume because not all the liquid is vaporised in the syringe, so the Mr is too large.

Question 22

What is the empirical formula?

Answer 22

It is the simplest (whole number) ratio of the number of atoms of each element present in a molecule

Question 23

What is the molecular formula?

Answer 23

It is the actual number of atoms of each element in one molecule of a compound.

Question 24

What are the steps to find the empirical formula?

Answer 24

1. Write atoms in ratio
2. Write percentages in ratio
3. Divide by Ar
4. Divide by smallest mol for a whole number ratio in simpliest form

Question 25

What are spectator ions?

Answer 25

They are ions that are chemically unchanged at the end of a reaction

Question 26

What are the rules for ionic equations?

Answer 26

1. Make sure the equation is balanced 2. Only write chemicals that are (aq) as ions (apart from elements) 3. Make sure both sides are balanced 4. Cancel any species that are identical either side of the arrow

Question 27

What are the rules of predicting masses in chemical reactions?

Answer 27

1. Ensure you have a balanced equation 2. Calculate moles 3.Use ratios in the equation to get moles of the unknown 4. Convert back to mass

Question 28

What is the yield of a chemical?

Answer 28

The amount of product formed

Question 29

Why would the actual yield be much less than the theoretical yield?

Answer 29

Some of the products may be left in the container or the reaction may not go to completion (reversible) or the reactants are reversible

Question 30

What is the equation for calculating percentage yield?

Answer 30

Percentage yield= Actual yield / theoretical yield x 100

Question 31

What is the equation for atom economy?

Answer 31

Atom economy= Mass of desired product / total mass of reactants or products x 100 Or Mr

Question 32

Is 100% atom economy possible?

Answer 32

Yes only if one product if formed

Question 33

Describe the ,method for making up a standard solution?

Answer 33

- Weigh out the sample in weighing boat and transfer to beaker - Re - weigh the boat and calculate the mass added ( Weighing by difference) - Dissolve sample in distilled water and add into a volumetric flask with the washings of the glass rod, funnel and beaker - Make up to 250cm^3 in volumetric flask, near the 250 mark and use a pipette to ensure that the bottom of the meniscus is on the 250cm^3 mark - Invert to give a homogenous solution

Question 34

What are the steps during a titration?

Answer 34

-Fill a burette with the acid of a known concentration after rinsing and ensure there no air bubbles. -Accurately measure an amount of the alkali using a calibrated pipette and pipette filler after rinsing. -Add the alkali to a conical flask with a few drops of a suitable indicator (phenolphatlein) -Run in the acid from the burette and swirl the flask until the colour just changes, showing that the solution in the conical flask is now neutral-This is a rough titre - Repeat the procedure until three values for the volume of acid used at neutralisation are the same, within experimental error. Concordant results are within 0.1cm^3 of each other.

Question 35

Why do you rinse the conical flask near the end point?

Answer 35

To add reagents back to flask

Question 36

Why do you wash the burette with water before titration?

Answer 36

To remove any soluble impurities

Question 37

Why do you wash the burette with the solution that will be used?

Answer 37

To ensure that the concentration of the solution is not changed by water

Question 38

How do you reduce error in a burette?

Answer 38

Use larger volumes of solutions by decreasing the concentration

Question 39

How do you convert grams into tonnes?

Answer 39

x (1x10^6)

Question 40

How do you convert cm^3 to litres?

Answer 40

/1000