Amount Of Substances Flashcards by Jillandra Perriman

What is a mole

A measure of amount of substance

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What’s one mole of a substance

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

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What does 1 mole of anything contain

Avogadro’s number- 6.02 x 10 23
Na

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How do you find the actual number of any species

Get the moles of that species
Then x Na

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

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

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What is the equation for the mass of 1 atom

Mass of 1 mole/ avogadros number

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What is the equation for mass of 1 mole

Mass of 1 atom x Avogadro’s number

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What is the definition for empirical formula

The simplest whole number ratio of atoms in a cokpihnd

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

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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What is the definition of molecular formula

The actual number of atoms in a compihnd

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How do you calculate molecular formula

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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How do you calculate hydrated salts

The empirical formula

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

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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How do you measure mass of water lost

Mass of hydrated salt- mass of anhydrous salt

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

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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How do you know if you’re wrong

If the ratio of waters is smaller than the salt

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How do you measure percentage uncertainty

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

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How do you evaluate x for water lost

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

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Some hydrated solid spat out during heating

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

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What if the lid wasn’t put on when cooling

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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How can you make improvements to deter percentage uncertainty

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

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What is the equation for moles of a gas

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

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How can you tell that you need to use this equation

if it contains cm3 or dm 3

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

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

What is the number for the gas constant (R)

8.314

How do you convert degrees Celsius to degrees Kelvin

+273

How do you convert kPa to Pa

x1000

How do you convert cm3 to m3

divide by 1000000 x 1000000

What is solution

A solute dissolved in a solvent

What is the concentration

Moles of a solute per 1dm-1 of water

What is the equation for the moles of a solution

concentration x volume

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

times it by the Mr

What is a standard solution

A solution with a known concentration

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

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

What tells us the molar ratios

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

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

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

What are titrations used for

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

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

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

How can you find the mass using molar ratios

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

What are titrations

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

What is the theory of titrations

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 )

How do you work out an acid base titration

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

When do you need to scale up or down

When it’s a titration of a standard solution

How do you scale up

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

What is monoprotic

Acids with one H+ ion (HX)

What is diprotic

Acids with 2 H+ ions (H2X)

What does percentage yield tell you

The efficient of a reaction

How do you calculate percentage yield

Actual moles/ theoretical moles X 100

Why is it better to base your calculation on miles

Using mass can lead to misconceptions and mistakes

What does atom economy tell us

About how much waste a reaction creates

What is the equation for atom economy

Mr of desired products x 100 Mr of all products.

What is the limiting reagent

The reagent that has depleted first

What is the excess reagent

The reagent that contains more moles than we need

How do you work out limiting reagent

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

What does atom economy tell us about

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