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Chemistry > Unit 1: Section 2: Amount of substance > Flashcards

Unit 1: Section 2: Amount of substance Flashcards

1
Q

What is a mole

A

6.02 x 10^23 particles

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2
Q

How would you work out how many particles are in 0.450 moles of iron

A

0.450 x 6.02 x 10^23

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3
Q

How do you work out the mass of 1 mole of a element or compound

A

It’s the same as the Mr

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4
Q

What is the equation that links mass, moles and Mr

A

Number of moles = mass/Mr

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5
Q

What is the concentration of a solution and what is the unit

A

How many moles are dissolved per 1 dm ^3 of solution. The units are mol dm^-3

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6
Q

What is the equation that links number of moles and concentration

A

Number of moles = Concentration x Volume (cm^3) / 1000

OR

Number of moles = Concentration x Volume (dm^3)

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7
Q

What is the purpose of the ideal gas equation

A

Lets you find the number of moles in a certain volume at any temp or pressure

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8
Q

What is the ideal gas equation

A

Pressure (Pa) x Volume (m^3) = Number of Moles x Gas Constant (8.31 J K^-1) x Temp (Kelvin)

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9
Q

How do you convert from Celsius to Kelvin

A

Add 273

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10
Q

How do you derive an ionic equation from an equation

A

Make sure it is balanced
Split up into ions
Cross out the ions that are in both reactants and products

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11
Q

Find the mass of Iron (III) oxide produced when 28g of Iron is burnt in air

A

2Fe(s) + 1.5O2 -> Fe203(s)
Work out how many moles of iron - 28/55.8 = 0.502 moles of iron
Molar ratio of Fe : Fe2O3 is 2:1 so 0.502/2 = 0.251
Mr of Fe2O3 = 159.6
159.6 x 0.251 = 40 g

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12
Q

What do you have to do before a titration

A

Make a standard solution

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13
Q

What does aqueous mean

A

Solution in water

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14
Q

What is neutralisation

A

When an acid reacts with an alkali you get a salt and water

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15
Q

What is a standard solution

A

Any solution that you know the exact concentration of

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16
Q

How do you make a standard solution

A

Dissolve a known amount of solid in a known amount of water to create a known concentration

17
Q

What is another word for standard solution

A

Volumetric solutions

18
Q

How would you make a standard solution for sodium hydroxide

A

Work out the moles using concentration x volume
Work out mass using mass/Mr
Place weighing bottle on digital balance - weight required mass of solid and tip into beaker
Weigh weighing bottle and subtract the mass of bottle from mass of solid
Add distilled water to beaker and stir until sodium hydroxide has dissolved
Tip solution into volumetric flask and use a funnel to make sure all of it go on
Rinse beaker, stirring rod and funnel with distilled water and add that to the flask too
Top flask up to correct volume with distilled water (make sure bottom of meniscus reaches the line)
Mix contents of flask
Then calculate the concentration of the solution

19
Q

How do you perform titrations

A

Use pipette to measure set volume of the solution that you want to know the concentration of
Put in a flask
Add a few drops of an appropriate indicator to the flask
Fill beaker with standard solution of the acid
Use funnel and pour acid into burette (do below eye level to avoid splashing)
Do rough titration to find out the end point (the point where the alkali is neutralised and the indicator changes colour)
Then do accurate titration - take initial reading, then run the acid in to within 2cm^3 of the end point
Find amount of acid needed to neutralise the alkali by subtracting the final reading rom the initial reading (this is called a titre
Repeat a few times until you have three results within 0.1cm^3 of each other (concordant)
Use results from each to find the mean volume of acid used
Leave out any anomalous results

20
Q

What type of indicators are used in titrations

A

Ones that change colour quickly over a very small pH range so you know exactly when the reaction has ended

21
Q

What are the two indicators used in titrations

A

Methyl orange
Phenolphthalein

22
Q

What are the colours of methyl orange in alkalis and acids

A

Alkali - Yellow
Acid - Red

23
Q

What are the phenolphthalein in alkalis and acids

A

Alkali - Pink
Acids - Colourless

24
Q

What is the equation for volume

A

Concentration x Volume (dm^3)

25
Q

Give the difference of the empirical and the molecular formula

A

Empirical gives ratio of atoms in compound and molecular gives the exact amount of atoms in the compound

26
Q

A molecule has an empirical formula of C4H3O2, and a relative molecular mass if 166. Work out its molecular formula

A

(4x12) + (3x1) + (2x16) = 83
166/83 = 2
2 x C4H3H02 = C8H6O4
C8H6O4 is the molecular formula

27
Q

Compound is found to have percentage composition 56.5% potassium, 8.7% carbon and 34.8% oxygen by mass. Calculate its empirical formula

A

Assume its 100g of the compound
56.5 g = Potassium
8.7g = Carbon
34.8g = Oxygen
56.5/39.1 = 1.45 moles
8.7/12 = 0.725 moles
34.8/16 = 2.18 moles
1.45/0.725 = 2
0.725/0.725 = 1
2.18/0.725 = 4
K2CO3

28
Q

What is the theoretical yield

A

The mass of a product that should be formed in a chemical reaction

29
Q

What is the formula for percentage yield

A

(Actual Yield / Theoretical Yield) x 100

30
Q

What is atom economy

A

A measure of the proportion of reactant atoms that become a part of the desired product in the balanced chemical equation

31
Q

What are the economic advantages to a high atom economy

A

More efficient use of a company’s raw materials
Low atom economies will require large amounts of raw materials to produce the same amount and this will cost a lot of money
There will be less waste to deal with

32
Q

What are the environmental and ethical advantages to a high atom economy

A

Many raw materials are in limited supply so they should be used as efficiently as possible so they can last longer
Producing less waste is better for the environment
More sustainable
If the process is more efficient it will be cheaper which can also lead to low prices for medicines so it is more accessible

33
Q

What is the formula for percentage atom economy

A

% Atom Economy = (Molecular Mass of Desired Product / Sum of Molecular Masses of all Reactants) x 100

Chemistry (7 decks)

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