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chemistry > topic 5 > Flashcards

topic 5 Flashcards

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1
Q

what is a mole definition

A

measuring amount of substance

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2
Q

what number is a mole

A

avogadros number
6.02 x 10^23 atoms/molecules

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3
Q

how to work out number of particles

A

avogadros x moles

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4
Q

how to work out moles

A

mass / Me

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5
Q

cslculate the number of moles in 23g of gold

A

23/197
= 0.12 mol

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6
Q

how to work out moles in solution

A

conc. (moldm-3) x vol (dm3)

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7
Q

how to work out conc. in gdm-3

A

mass/vol

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8
Q

calculate moles of 200cm3 of 0.35 moldm-3 HCl

A

0.35 x 200x10-3
= 0.07 mol

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9
Q

what is empirical formula

A

simplest whole number ratio of elements in a compound

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10
Q

how to work out empirical formula

A
  1. write out elements involves
  2. write % as masses
  3. divide these by Mr to get moles
  4. divide all by smallest number of moles
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11
Q

work out empirical formula od a compound that contains 23.3% Mg, 30.7% S, 46% O

A
  1. Mg S O
  2. 23.3g 30.7g 46g
  3. 24.3 32.1 16
    = 0.96 0.96 2.88
  4. 1 1 3

MgSO3

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12
Q

work out the empirical formula when a hydrocarbin combusts completely to make 0.845g of CO2 and 0.173g H2O

A

1write H2O and CO2 headings
2. write doem masses
3. divide by Mr to get moles
4. divide number of C and H atoms by smallest moles

CO2 H2O
0.845g 0.173g
——— ———
44 18
=0.019 =0.0096x2=
0.0192
/ 0.019=1 /0.019=1

CH

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13
Q

how to work out molecular formula from empirical

A

work out Me of empirical/ Mr molecular
x atoms in empirical

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14
Q

what do ionic equations show

A

ions formed in solution and which particles are reacting

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15
Q

how to work out ionic equations

A

axe aq
ditich doubles

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16
Q

what is the ionic equation of H2SO4 + 2KOH –> K2SO4 + 2H2O

A

2H^+ + SO4^2- + 2K^+ + 2OH^- –> 2K^+ + SO4^2- + 2H2O

2H^+ + 2OH^- —> 2H2O

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17
Q

how to work out theoretical masses

A
  1. write equation and balance
  2. work out Mr and write as masses
  3. find 1 gram of compound you know the mass of x mass, divide other compound by this and x same
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18
Q

how much CaO can be made when 34g Ca burnt in O2

A
  1. 2Ca(s) + O2 (g) —> 2CaO (s)
  2. 40x2 = 80g 56x2 =112g
  3. /80=1g /80=1.4
    x34 = 34g x34 = 47.6g

= 47.6g

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19
Q

what is a displacement reaction

A

more reactive element takes place of less reactive element in compound

20
Q

what is an acid base reaction

A

form salt and water
carbonates produce carbon dioxide as well

21
Q

what is a precipitation reaction

A

solid produced after 2aq reactants react

22
Q

how to work out moles from volume and molar gas volume

A

volume/molar gas volume

23
Q

what is molar gas volume at room temperature and pressure

A

24 dm3 mol-1

24
Q

what is molar gas volume at standard temperature and pressure

A

22.4 dm3 mol-1

25
Q

how much gas in cm3 is produced when 6.2g of Mg reacts with HCl at rtp

A

Mg(s) + 2HCl(aq) —> MgCl2 (aq) + H2 (g)
Mr Mg = 24.3
mol Mg = mass/Mr = 6.2/24.3 = 0.255 mol
Mg:H2 1:1 ratio so H2 mol = 0.255
volume = mol x molar gas volume = 0.255 x 24 = 6.12 dm3
= 6120 cm3

26
Q

calcualte amount of gas produced when 5.6 dm3 of N2O decomposes

A

N2O (g) —> N2(g) + 0.5 O2(g)
1 mol N2O produces 1 mol N2 and 0.5 mol O2
1.5 mol produced overall
1.5x5.6 = 8.4 dm3

27
Q

what is the ideal gas equation and all units

A

pV=nRT

p- pressure (Pa)
v- volume (m3)
n- moles
R - gas constant 8.31 JK-1mol-1
T - temperature (K)

28
Q

how to convert m3 to dm3 to cm3

A

m3–>dm3 ‘
x1000
dm3–>cm3 x1000

29
Q

what volume of H2 produced when 12g of K reacts with H2O at 100KPa and 298K, gas constant 8.31

A

2K(s) + 2H2O (l) –> 2KOH (aq) + H2(g)
mass/ Mr 12/39= 0.31mol of K
2 moles K produces 1 mol H2 0.31/2=0.155 mol H2
v=nRT/p
v = 0.155x8.31x298/100,000
= 3.84x10^-3 m3

30
Q

what is a hazard

A

things that could cause harm

31
Q

what is a risk

A

likelihood of harzard causing harm
eg
scalding from hot liquids
burns from hot equipment
burns from chemicals
cuts from glass/metals

32
Q

what is a risk assessment

A

identification of all hazards and risks associated
likelihood of something going wrong
seriousness of risk
how to reduce risk

33
Q

how to make a standard solution

A

weigh - weigh amount of solid precisely using balance and weighing boat
transfer- transfer solid from weighing boat to beaker, wash any solid left into beaker using distilled water
disolve- dissolve solid fully using distilled water, stir to ensure fully disolved
transfer- transfer solution to volumetric flask using funnel, rinse beaker and glass rod into flask
fill- use more distilled water to fill to graduation line, use pipette when near
mix - invert flask to ensure solution fully mixed

34
Q

what mass of solid NaOH is required to make 250c,3 of 0.75 mol dm-3 NaOH solution

A

work out moles
conc. x vol
0.75 x 250x103 = 0.1875 mol

use moles to calculate mass
mol x Mr
0.1875 x 40 = 7.5g

35
Q

how does a titration take place

A

have known acid or alkali in burette with known conc.

have known volume of unknown acid or alkali conc. in conical flask

add chemical in burette to conical flask until indicator changes

read how much chemical was added to neutralise chemical in flask, read from bottom of meniscus

36
Q

18.3 cm3 0.25 moldm-3 HCl required to neutralise 25cm3 KOH, calculate conc. KOH

A
  1. write equation and balance
    HCl + KOh –> KCl + H20
  2. calculate moles of HCl conc x vol
    0.35 x 18.3x10-3 = 4.58 x10-3 mol
  3. use equation to find molar ratio
    1:1 HCl : KOH
    moles KOH = 4.58 x10-3
  4. conc.= moles/vol
    4.58x10-3 / 25x10-3 = 0.18 mol
37
Q

what is an uncertainty

A

degree of error your measurements have
hald the smallest increment on equipment
if you are using more then one measurement with the same units you add uncertainties

38
Q

how to calculate % uncertainty

A

uncertainty / reading
x100

39
Q

what are systematic errors

A

caused every time

40
Q

what are random errors

A

caused through estimating readings
vary

41
Q

how to calculate % yeild

A

actual/theortical
x 100

42
Q

what is theoretical yield

A

amount of product produced assuming no products lost and all reactants fully react

43
Q

how to calculate atom economy

A

Mr of desired product / sum of Mr of all reactants
x100

44
Q

what is atom economy

A

how efficient a reaction is

45
Q

what is the importance of atom economy

A
  • high atom economies produce less waste so benefit environment
  • high atom economies means that raw materials are used more efficiently, more sustainable
  • companies will try to use reactions that tend towards 100% atom economies
  • high atom economy means less by products so less time and money separating these from desirable product

chemistry (15 decks)

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