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Chemistry > Calculations Involving the Mole > Flashcards

Calculations Involving the Mole Flashcards

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1
Q

What charge is an Al ion

A

Al3+

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2
Q

What ion does Zn form

A

Zn2+

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3
Q

What ion does Ag form

A

Ag+

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4
Q

When do you use the suffix “ide”

A

When a non-metal reacts with one other element

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5
Q

What is the formula for an ammonium ion

A

NH4+

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6
Q

What is the formula for a nitrate ion

A

NO3-

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7
Q

What is the formula for a carbonate ion

A

CO3 2-

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8
Q

What is the formula for a sulfate ion

A

SO4 2-

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9
Q

What is the formula of aluminium oxide

A

Al3+ O2-
Drop and swap method
Al2O3

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10
Q

What is the difference between molecular and empirical formula

A

Empirical - ratio of atoms in element
Molecular - exact amount of atoms in molecule

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11
Q

What is the relative molecular mass

A

The weighted mean mass of a molecule compared with 1/12th the mass of an atom of carbon-12

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12
Q

What is the molecular mass of C2H4Cl2

A

(2x12) + (4x1) + (2x35.5) = 99

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13
Q

How do you calculate relative molecular mass

A

Add up the relative molecular mass of all the atoms in the molecule

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14
Q

How do you calculate the relative formula mass

A

The same way as calculating the molecular mass but using the empirical formula instead

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15
Q

What does the Avogadro’s constant represent

A

The number of particles of a substance in one mole of that substance

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16
Q

What is molar mass

A

The mass of one mole of a substance

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17
Q

What are the units for molar mass

A

g mol^-1

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18
Q

How do you work out the molar mass for an element, molecule and a giant structure

A

Element - Relative atomic mass
Molecule - Relative molecular mass
Giant structure - Relative formula mass

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19
Q

What is the formula for working out amount of substance

A

Amount of Substance = Mass (g) / Molar Mass (g/mol)

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20
Q

Ca = 40.1
Cl = 35.5
Calculate the amount of substance in 388.85 g of CaCl2

A

Calculate relative formula mass of calcium chloride - 40.1 + 71 = 111.1
388.5/111.1 = 3.5 mol

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21
Q

What is the formula for the number of particles in a substance

A

Amount of substance (mol) x the Avogadro constant

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22
Q

Calculate the number of atoms in 81 g of Al (Ar=27)

A

Molar mass = 27
Amount of substance = 81/27 = 3 mol
3 x Avogadro constant = number of particles

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23
Q

Calculate the number of electrons in 98.9 g of sodium

A

Amount of substance = 98.9/23 = 4.3 mol
4.3 x Avogadro constant = number of particles
Ans x 11 = number of electrons

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24
Q

What is the unit of volume always used

A

dm^3

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25
What is the unit of concentration
mol dm^-3
26
21.25 g of NaNO3 was dissolved in water The final volume of the solution was 125 cm^3 Calculate the concentration of the solution
21.25/85 = 0.25 mol 125 cm^3/1000 = 0.125 dm^3 0.25/0.125 = concentration
27
What is the volume of one mole of any gas
Approximately 24 dm^3
28
What is room temperature and pressure
Temp - 20 degrees Celsius Pressure - 101000 Pa`
29
How do you work out the volume if you don't have the concentration
Moles x 24
30
A sample of CO2 has a volume of 3.6 dm^3 at room temperature and pressure. Calculate the number of moles of CO2
Moles = vol/24 3.6/24 = 0.15 moles
31
What is the ideal gas equation
Pressure x Volume = Number of Moles x Gas Constant x Temperature
32
What are the units of the components of the ideal gas equation
Pressure = Pa Volume = m^3 Number of moles = mol Gas constant = J mol^-1 K^-1 Temperature = Kelvin
33
What is the ideal gas constant
8.314 J mol^-1 K^-1
34
How do you convert celsius to kelvin
Add 273
35
Describe the experiment carried out when you need to calculate the molar mass using the ideal gas equation
Take gas syring with small cap on the end Use balance to find mass of empty syringe and cap Remove cap - draw small vol of chemical into syringe Replace cap to seal gas into syringe Reweigh syringe containing chemical and cap Subtract initial mass of empty syring plus the cap from the mass of syring containing the chemical plus the cap Boil chemical so it turns from liquid to gas - place syringe into beaker with boiling water Once it is boiled we can read the vol of gas from the scale on the syringe
36
Why does the experiment to work out the molar mass using the ideal gas equation doesn't work if the chemical has a boiling point above 100 degrees and what will you have to do if this is the case
Because water has a boiling point of 100 degrees Need to use an oil-bath
37
A sample of a compound was found to contain 55.56g of carbon and 9.29 grams of hydrogen Determine the empirical formula of this compound
Find the moles of each element by dividing each by the relative atomic mass 55.56/12 = 4.63 9.29/1 = 9.29 To find the simplest whole number ratio divide by the smallest number 4.63/4.63 = 1 9.26/4.63 = 2.007 So empirical formula is CH2
38
A compound contains 31.6% carbon, 5.3% hydrogen and 63.1% oxygen Determine the empirical formula of this compound
Divide percentages by Mr to find the moles Divide each by the smallest number of moles C2H4O3
39
A compound contains 43.66% phosphorus and 56.34% oxygen. The compound has a relative molecular mass of 284 g/mol Determine the empirical formula of the compound and the molecular formula
Work out empirical formula Divide relative molecular mass by relative mass of empirical formula 284/147 = 2 P2O5 x 2 = P4O10
40
How is water of crystallisation shown in formula
Dot in the middle Salt·xH2O
40
What does anhydrous mean
Doesn't contain water of crystallisation
41
What is water of crystallisation
When compounds contain water molecules bonded into the crystal structure
42
Hydrated magnesium sulfate has a relative formula mass of 246.4 g/mol MgSO4·xH2O Determine the value of x
The relative formula mass of MgSO4 = 120.4 246.4-120.4 = 126 Each water molecule's Mr = 18 g/mol 126/18 = 7 x = 7
43
Describe the experiment carried out to find the value of water of crystallisation
Weigh empty boiling tube using balance Place several spatulas of hydrated compounds into boiling tube - weight tube again Calculate mass by subtracting mass of boiling tube from mass of boiling tube with hydrated compounds Heat boiling tube over a roaring bunses burner flame - drives of water of crystallisation as steam Weigh boiling tube every couple of minutes until it stops decreasing and your left with anhydrous crystal Calculate mass of crystal by subtracting mass of boiling tube with mass of boiling tube with crystal in it
44
What are the problems with the water of crystallisation experiment
If value is less than expected then that suggests that not all of the water molecules were driven off during heating If value is greater than expected then that suggests that the compound has underwent further decomposition into another compound
45
How do you prepare the alkali in a conical flask
Use pipette (vol of 25 cm^3) to measure known volume of alkali Rinse pipette with distilled water to remove any unwanted chemicals Rinse pipette with alkali to discard any water that would dilute solution Rinse conical flask to remove traces of unwanted chemicals Draw alkali into pipette using a pipette filler - do slowly to avoid bubbles Make sure to fill above the 25 cm^3 mark because the level will drop slightly Need bottom of meniscus at 25cm^3 - view meniscus at eye level Release alkali into conical flask Add a few drops of indicator
46
With a strong acid strong base titration what indicators could we use
Phenolphthalein Methyl Orange
47
With a weak acid strong base titration would indicators do we use
Phenolphthalein
48
With a strong acid weak base titration what indicators do we use
Methyl Orange
49
Why is it important to not add a lot of drops of indicator
Indicators are weak acids so if we add a lot that could give us inaccurate results
50
Explain how you use a burette to measure th volume of acid that reacts with an alkali
Rinse burette with distilled water to remove unwanted chemicals from burette Rinse with acid to remove any traces of water Clamp burette so it's level Use funnel and slowly fill burette with acid Make sure level of acid is slightly above the zero line Remove funnel - prevents acid from dripping from funnel into burette Open tap and let acid drip slowly into burette until meniscus is at the 0 cm^3 mark Place conical flask containing the alkali onto a white tile Open tap on burette and slowly release acid into conical flask At the same time we swirl the conical flask so the alkali and the acid mix thoroughly Stop adding acid to show the end point then read the level of the burette
51
What is the uncertainty of a burette
The scale markings are to the nearest 0.1cm^3 The uncertainty is considered to be half the scale division for an analogue piece of equipment So it is 0.05 cm^3
52
Describe an experiment necessary to work out the molar mass of sodium carbonate
Use balance with two decimal places - place weighing boat and set balance to 0 Add around 1.5 g of hydrated sodium carbonate Transfer to beaker Reweigh weighing boat and calculate mass of sodium carbonate added to beaker because not all of the sodium carbonate will be added to beaker Add 100 cm^3 of distilled water to beaker - dissolve sodium carbonate using stirring rod Use funnel to transfer the solution to a 250 cm^3 volumetric flask Rinse beaker and stirring rod with distilled water - transfer rinsed water to volumetic flask so all the compound is in the flask Slowly fill volumetric flask with distilled water - level is just below 250 cm^3 mark (use pipette at the end)
53
What is the formula for atom economy
Molecular mass of desired product / Sum of molecular masses of all reactants x 100
54
Why are reactions with a high atom economy more stable then a low atom economy reaction
Less reactants turn into waste products
55
What is the equation for percentage yield
Actual yield / Theoretical yield x 100
56
Why is maximum theoretical yield rare
Not all reactants may react especially in reversible reactants Side reactions may take place Some product may be lost
57
What is the excess reagent
When there is some of the product left over after a reaction
58
What is the limiting reagent
The chemical used up first in a reaction
59
How can you tell what the limiting reagent is
The reactant that has the lowest amount of moles
60

Chemistry (6 decks)

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