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chemistry: physical chemistry 1 > amount of substance > Flashcards

amount of substance Flashcards

1
Q

how do you convert from cm^3 to dm^3?

A

divide by 1000

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2
Q

how do you convert from dm3 to cm3?

A

multiply by 1000

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3
Q

what is relative atomic mass?

A

● mass of each atom

● always to 1 d.p

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4
Q

what is the definition of relative atomic mass?

A

average mass of an atom relative to C−12 on a scale in which an atom of C−12 has a mass of 12

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5
Q

what is the definition of relative molecular (formula) mass?

A

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

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6
Q

how do you calculate relative atomic mass?

A

(% abundance 1 x mass of isotope 1) + (abundance 2 x mass of isotope 2)

/ 100 (or total abundance)

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7
Q

what is avogadro’s constant?

A

6.022 x 10^23

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8
Q

what is the sig fig rule?

A

● generally 3 sig figs

● give answer the same amount of sig figs as the sig figs of the numbers in the question

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9
Q

what is molar mass?

A

numerically the same as Mr but in g / mol

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10
Q

what is the calculation for moles?

A

m = m / mr

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11
Q

what is the calculation for number of molecules?

A

number of molecules = moles x avogadro’s number

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12
Q

what is the calculation for number of atoms?

A

number of atoms = moles x avogadro’s number x number of atoms in molecule

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13
Q

what is the calculation for concentration?

A

c = n / v

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14
Q

what is a solute?

A

solid that dissolves in solvent to form a solution

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15
Q

what is a solution?

A

mixture formed when solute dissolves in solvent

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16
Q

what is a solvent?

A

the liquid in which a solute dissolves

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17
Q

what is the calculation for concentration using gdm^-3?

A

c = mass / v

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18
Q

how do you go from cm^3 to dm^3?

A

divide by 1000

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19
Q

how do you convert from moldm^-3 to gdm^-3?

A

x Mr

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20
Q

how do you convert from gdm^-3 to moldm^-3?

A

/ Mr

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21
Q

what is the dilution factor?

A

● initial conc / target conc

● sum of the parts

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22
Q

what is whatever you are diluting equal to?

A

one part

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23
Q

what is the calculation for % uncertainty?

A

% uncertainty = (instrument uncertainty / quantity measured) x 100

24
Q

how do you improve accuracy?

A

larger volume, larger mass as it decreases % uncertainty

25
Q

what is the ideal gas equation?

A

PV = nRT

P - pressure (Pa) (N/m^2)
V - volume (m^3)
n - number of moles
R - 8.31JK^-1mol^-1
T - temp (K)

26
Q

how do you convert from degrees celsius to kelvin?

A

+273

27
Q

how do you convert from kelvin to degrees celsius?

A

-273

28
Q

how do you convert from kPa to Pa?

A

x 10^3

29
Q

how do you convert from dm^3 to m^3?

A

x 10^-3

30
Q

how to convert from cm^3 to m^3?

A

x 10^-6

31
Q

how do you write ionic equations?

A

● make sure equation is balanced

● only write chemicals that are (aq) as ions

● make sure both sides are balanced

● cancel out any species that are identical either side of the arrow

32
Q

what are spectator ions?

A

ions that are chemically unchanged at the end of a reaction

33
Q

what is the calculation for percentage yield?

A

actual / theoretical x 100

34
Q

what is theoretical yield?

A

number of moles or mass obtained by calculation

35
Q

what is the actual yield?

A

number of moles or mass of product obtained experimentally

36
Q

what is percentage yield?

A

shows how much of a particular product you get from the reactants compared to the maximum theoretical amount that you can get

37
Q

what is atom economy?

A

shows how many atoms used in reaction become desired product

38
Q

what is the calculation for atom economy?

A

mass (or mr) of desired product / total mass (or mr) of reactant (or product) x 100

39
Q

what does atom economy take into account?

A

the big number

40
Q

when is atom economy 100%?

A

when there’s 1 product

41
Q

what is the method for making a volumetric solution and carrying out a simple acid-base titration?

A

● weigh sample out in boat

● transfer to beaker

● reweigh boat, calculate mass added (weighing by difference - to ensure that we know what solid has actually been transferred)

● dissolve sample in distilled water (must be less than 250cm3)

● add into volumetric flask with washings of glass rod, funnel, beaker (washings to ensure all of solid is in solution)

● make up to 250cm3 in volumetric flask, near 250cm3 graduation mark use pipette, ensure bottom of meniscus on 250cm3 mark

● invert (to give a homogenous solution rather than to dissolve)

42
Q

what are the steps of titration?

A

● fill burette with acid of known conc after rinsing with NO air bubbles

● accurately measure amount of alkali using calibrated pipette and pipette filler after rinsing

● add alkali to conical flask with few drops of suitable indicator

● run in acid from burette and swirl flask until colour just changes showing solution in conical flask is neutral - rough titre

● repeat procedure until 3 values for volume of acid used at neutralisation are same, within experimental error

● concordant results are within 0.1cm^3 of each other

43
Q

how do you prepare and use a burette?

A

● washing with water 3 times - removes any soluble impurities

● washing with solution the used to fill burette - ensures conc not changed by water

*applies for pipette

● use funnel to fill burette - don’t leave in funnel - drops could affect volume

● if air bubble left in burette, space will be filled during titration causing volume added to be too high

44
Q

how do you read from a burette?

A

● from bottom of meniscus

● readings taken from 2 d.p.

45
Q

how do you use indicator?

A

● 1-3 drops

● if too much pH may change as its acidic

46
Q

why do we use a conical flask?

A

● less chance of losing liquid when swirling

● easier to swirl contents

47
Q

how do you rinse a conical flask?

A

● near end point wash sides of conical flask with distilled water - returns reagents to reaction mixture

● does not affect accuracy as water does not change moles of each reagent

48
Q

how do you see colour change?

A

use white tile

49
Q

how to go from milligrams to grams?

A

divide by 1000

50
Q

what is the empirical formula?

A

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

51
Q

what is the molecular formula?

A

actual number of atoms of each element in one molecule of the compound

52
Q

why is the actual yield much less than the theoretical yield?

A

● reactants may be impure

● reaction may not go to completion

● some of the product may be left in the container

● it may be difficult to purify the product

53
Q

how do you reduce error from burette?

A

● use larger volumes of solution

● must decrease concs of solution you are using in burette to ensure you are using larger volumes

54
Q

why do you swirl the conical flask during a titration?

A

to ensure the complete mixing of reactants

55
Q

what is the rough titre?

A

● the first titre you perform

● to get an approximate titre

● as single titre could be flawed / anomalous

● never include rough titre in an average

56
Q

what is the general method for a back titration?

A

● react a known mass of solid to be analysed with an excess (but known) amount of acid

● make up excess acid to a specific volume and titrate against a standard base

● calculate the amount of acid remaining (the excess)

● calculate amount of acid used up in original reaction by subtraction from initial number of moles

● calculate number of moles present the original solid by consideration of the stoichometry of reaction

57
Q

what are the uses of back titrations?

A

● finding relative formula mass of an unknown carbonate

● identifying metal in an unknown metal oxide

● finding the percentage of metal in an alloy

● finding purity of an impure carbonate or oxide

chemistry: physical chemistry 1 (5 decks)

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