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Chemistry Module 2- Foundations In Chemistry > Amount Of Substances > Flashcards

Amount Of Substances Flashcards

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1
Q

What is a mole

A

A measure of amount of substance

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2
Q

What’s one mole of a substance

A

Contains as many particles of that substances as there are carbon atoms in exactly 12g of carbon 12

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3
Q

What does 1 mole of anything contain

A

Avogadro’s number- 6.02 x 10 23
Na

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4
Q

How do you find the actual number of any species

A

Get the moles of that species
Then x Na

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5
Q

For example how many moles of Cl- are in 1 mole of MgCl2

A

2 moles of Cl-
Cl- ions= 2 x Na

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6
Q

What is the equation for the mass of 1 atom

A

Mass of 1 mole/ avogadros number

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7
Q

What is the equation for mass of 1 mole

A

Mass of 1 atom x Avogadro’s number

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8
Q

What is the definition for empirical formula

A

The simplest whole number ratio of atoms in a cokpihnd

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9
Q

What is an example of finding emp formula for 72% of magnesium and 28% of nitrogen

A

Mg. N
Mass. 72. 28
Mole. 2.9. 2
Ratio. 1.45. 1
Times both by 2 to get the whole number
Mg3N2

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10
Q

What is the definition of molecular formula

A

The actual number of atoms in a compihnd

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11
Q

How do you calculate molecular formula

A

To get the ratio you need.
Molar mass / empirical mass
To get the molecule formula it’s
Ratio x emp formula

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12
Q

How do you calculate hydrated salts

A

The empirical formula

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13
Q

How do you use the empirical formula to calculate the x number of waters

A

If you hear a hydrated salt the water of crystallisation will be removed by evaporation
You must hear to a constant mass to ensure that all the water of crystallisation is removed

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14
Q

How do you measure mass of water lost

A

Mass of hydrated salt- mass of anhydrous salt

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15
Q

MgSO4 x H2O weighed 4.312 g
After hearing the anhydrous salt weighed 2.107 g

A

Mass of H20 = 4.312-2.107=2.205
MgSO4. H2O
Mass. 2.107. 2.205
Moles. 0.0175. 0.01225
Ratio. 1. 7
7 waters are in the compind

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16
Q

How do you know if you’re wrong

A

If the ratio of waters is smaller than the salt

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17
Q

How do you measure percentage uncertainty

A

Number of reading (2/1) x uncertainty of équipement
Divided by your reading
Times by 100

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18
Q

How do you evaluate x for water lost

A

Mass of water lost increases/decreases?
Moles of water lost increased/decreased
Value of x is larger or smaller?

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19
Q

Some hydrated solid spat out during heating

A

Mass of water lost will increase
Moles of water lost will increase
So the value of x will be larger

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20
Q

What if the lid wasn’t put on when cooling

A

Mass of water lost would decrease
Moles of water lost WOJLD decrease
X would be smaller as the water vapour in the atmosphere could skew the resukts

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21
Q

How can you make improvements to deter percentage uncertainty

A

Use larger amounts of species depending on the practical
Use more accurate equipment ( BE SPECIFIC)

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22
Q

What is the equation for moles of a gas

A

moles of a gase= volume/ 24 (dm3)
volume/24000 (cm3)

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23
Q

How can you tell that you need to use this equation

A

if it contains cm3 or dm 3

24
Q

What is the equation for moles of a gase NOT AT RTP

A

PV =NRT
pressure x volume= moles x gas constand x temperaure

25
Q

What is the number for the gas constant (R)

A

8.314

26
Q

How do you convert degrees Celsius to degrees Kelvin

A

+273

27
Q

How do you convert kPa to Pa

A

x1000

28
Q

How do you convert cm3 to m3

A

divide by 1000000
x 1000000

29
Q

What is solution

A

A solute dissolved in a solvent

30
Q

What is the concentration

A

Moles of a solute per 1dm-1 of water

31
Q

What is the equation for the moles of a solution

A

concentration x volume

32
Q

If it has to be given in gdm-3 what do you do

A

times it by the Mr

33
Q

What is a standard solution

A

A solution with a known concentration

34
Q

Example- What mass of HCl should be used to make 250 cm3 of 0.8 mol dm-3

A

volume = 250 cm3
moles =c x v = 0.8 x 250/1000= 0.2 moles
mass=moles x Mr = 0.2 x 36.5= 7.3

35
Q

What tells us the molar ratios

A

Balanced chemical equations
A+2B–> C+D

36
Q

Example - 100g of CaCO3 . How many grams of CO2 is formed

A

Step 1: Moles of calcium carbonate- 100//100.1=0.999
Step 2: Ratio- 1:1= 0.999 moles
Step 3- mass-0.999 x 44= 43.956

37
Q

What are titrations used for

A

accurately measure the volume of one solution like an acid that reacts completely with the volume of another solution like a base

38
Q

Example- 11.6 cm3 of 3 moldm-3 of sulfuric acid is required to neutralise 25 cm3 of NaOH solution
What is the concentraion of the NaOH solution

A

1) Equations- make sure to balance it
2) moles of known species- 11.6x3/1000 = 0.0348
3) Ratio 1:2 so 0.0348 x 2 0.0696
4) concentraion = 0.0696/0.025 is 2.78 mol dm -3

39
Q

How can you find the mass using molar ratios

A

1) find moles of the compound you e been given information on
2) deduce the moles of the desired compound using the molar ratio
3) calculate the mass using mass is moles times Mr

40
Q

What are titrations

A

An experimental technique to accurately measure the volume of one solution that reacts exactly with another solution

41
Q

What is the theory of titrations

A

Conical flask has an exact volume of a solution with an unknown concentration
Burette is filled with a second solution of a known concentration
We use the burette to measure the volume required to fully react
(Can be other way round )

42
Q

How do you work out an acid base titration

A

1) write a balanced equation to get the molar ratio
2) find the moles of known solution
3) use molar ratio to deduce moles of unknown solution
4) use moles is cv to find unknown concentration

43
Q

When do you need to scale up or down

A

When it’s a titration of a standard solution

44
Q

How do you scale up

A

Divide the moles by the current volume and multiply by the new volume

45
Q

What is monoprotic

A

Acids with one H+ ion (HX)

46
Q

What is diprotic

A

Acids with 2 H+ ions (H2X)

47
Q

What does percentage yield tell you

A

The efficient of a reaction

48
Q

How do you calculate percentage yield

A

Actual moles/ theoretical moles X 100

49
Q

Why is it better to base your calculation on miles

A

Using mass can lead to misconceptions and mistakes

50
Q

What does atom economy tell us

A

About how much waste a reaction creates

51
Q

What is the equation for atom economy

A

Mr of desired products x 100
Mr of all products.

52
Q

What is the limiting reagent

A

The reagent that has depleted first

53
Q

What is the excess reagent

A

The reagent that contains more moles than we need

54
Q

How do you work out limiting reagent

A

1) work out the moles of both
2) decide the excess and limiting reagent so which is bigger and which is smaller
3) work out the mass using the limiting reagent ratio

55
Q

What does atom economy tell us about

A

The proportion of desired products compared with all the products formed in the reqction

Chemistry Module 2- Foundations In Chemistry (8 decks)

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