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Chemistry > C5 > Flashcards

C5 Flashcards

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1
Q

What is the weight of one mole of a substance equal to?

A

The relative formula mass (Mr)
Eg. Carbon has an Mr of 12, one mole of carbon weighs 12g
Nitrogen gas has an Mr of 28, one mole of nitrogen gas weighs 28g

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2
Q

What is molar mass?

A

The mass of one mole”

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3
Q

What is the equation for the number of moles?

A

Number of moles = mass in g / Mr

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4
Q

How many moles are there in 66g of carbon dioxide?

A

Mr = 44

Mass in g/Mr
66/44 = 1.5 moles

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5
Q

What is the relative atomic mass of an element?

A

The average mass of an atom of the element compared to the mass of 1/12th of an atom of carbon?12

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6
Q

What is concentration measured in?

A

Moles per dm (cubed)

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7
Q

What happens when you dissolve more solute in a given volume?

A

The more crowded the solute molecules are and the more concentrated the solution

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8
Q

What is the equation for concentration?

A

Concentration = number of moles / volume (in dm)

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9
Q

What is 1dm in litres and cm?

A 
1 litre
1000 cm (cubed)
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10
Q

What is the equation for mass (in grams?)

A

Mass = number of moles x Mr

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11
Q

What does an empirical formula give?

A

The smallest whole number ratio of atoms in a compound

Eg. C(2)H(6) = CH(3)

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12
Q

How do you work out empirical formulas?

A
  1. List all elements in compound
  2. Underneath, write their experimental masses or percentages
  3. Divide each mass or percentage by the Mr for that particular element
  4. Turn the numbers you get into a simple ratio by multiplying/dividing
  5. Get ratio in simplest form = empirical formula
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13
Q

What are titrations used for?

A

To find exactly how much acid is needed to neutralise a quantity of acid (or vice versa)

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14
Q

How do you carry out a titration?

5 points

A
  1. With pipette and pipette filler add some alkali into a conical flask with some indicator
  2. Fill a burette with acid
  3. Add the acid to alkali a bit at a time, giving the conical flask a regular swirl.
  4. The indicator changes colour when neutralised
  5. Record the volume used to neautralise the alkali
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15
Q

What indicator must be used in titrations? Why?

A

A single indicator eg. litmus (blue in alkali, red in acid)
? Universal indicator is used to estimate the pH of a solution because it turns a variety of colours. The colour gradually changes but during an acid based titration you want a sudden colour change

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16
Q

What 2 ways can gas be collected?

A
  1. Gas syringe

2. Upturned measuring cylinder or burette

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17
Q

What is an advantage and a disadvantage of using a gas syringe?

A

Advantage = Very accurate (give volumes to the nearest cm cubed)

Disadvantage = If the reaction is too vigorous then the plunger can be blown off

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18
Q

What can’t an upturned measuring cylinder/burette be used for?

A

Gases that dissolve in water like hydrogen chloride or ammonia

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19
Q

How can you measure the mass of gas produced?

A
  1. Carry out on a mass balance

2. As the gas is release, the mass disappearing is measured on the balance

20
Q

Which is the most accurate way to measure gas?

A

Measuring the mass because the mass balance is very accurate

21
Q

What is a disadvantage of a mass balance to measure the mass of gas produced?

A

It releases the gas straight into the room

22
Q

What volume does one mole of gas occupy?

A

24dm cubed at room temperature and pressure

Used in a question like What’s the volume of 4.5 moles of chlorine at RTP?” 4.5x24 = 108dm cubed”

23
Q

When does a reaction stop?

A

When all of one of the reactants are used up

Any other reactants are in excess

24
Q

What is the reactant that is used up in a reaction called?

A

The limiting reactant

25
Q

Why is the amount of product formed directly proportional to the amount of limiting reactant?

A

If you add more reactant, there will be more reactant particles to take part in the reaction = more product partiles

26
Q

What is a reversible reaction?

A

One where the products of the reaction can themselves react to product the orginal reactants

27
Q

How does the rate of the forward and backward reaction change?

A

As the reactants (A and B) react, their concentrations fall and so slows down.
As more and more products (C and D) are made, their concentrations rise and so speeds up

28
Q

What will happen after a while in a reversible reaction?

A

The forward and backward reaction will go at the same rate = EQUILIBRIUM

The concentrations have reached a balance and won’t change

29
Q

What does it mean when equilibrium lies to the right?

A

There are lots of products and not much of the reactants

30
Q

What does it mean when equilibrium lies to the left?

A

There are lots of reactants but not much of the products

31
Q

What does the position of equilibrium depend on?

A

The conditions

32
Q

What 3 things can change the position of equilibrium?

A

Temperature
Pressure
Concentration

33
Q

Why doesn’t adding a catalyst change the equilibrium position?

A

Catalysts speed up both forward and backward reactions by the same amount

34
Q

Why does temperature change the position of equilibrium?

A
  1. Decrease = the equilibrium will move to try and increase it (moves in exothermic direction to produce more heat)
  2. Increase = the equilibrium will move to try and decrease it (moves in endothermic direction)
35
Q

Why does pressure change the position of equilibrium?

A
  1. Decrease = the equilibrium tries to increase it (moves in the direction where there are more moles of gas)
  2. Increase = the equilbrium tries to decrease it (moves in the direction where there are fewer moles of gas)
36
Q

Why does concentration change the position of equilibrium?

A
  1. Increase conc of reactants = the equilibrium tries to decrease it by shifting to the right
  2. Increase cocn of products = the equilibirum tries to decrease it by shifting to the left
37
Q

What is the contact process used to make?

A

Sulfuric acid

38
Q

Explain the stages of the contact process

A
  1. Make sulfur dioxide usually by burning sulfur in air
  2. Sulfur dioxide is oxidised to make sulfur trioxide (REVERSIBLE REACTION)
  3. Sulfur trioxide is used to make sulfuric acid
39
Q

How is temperature controlled in the contact process?

A
  1. Oxidising sulfur dioxide = sulfur trioxide (exothermic)
  2. (To get more product, temperature would be reduced so the equilibirum would shift to replace heat) However reducing temp = slows rate down
  3. Compromise temperature of 450
40
Q

What compromise is made with pressure in the contact process?

A
  1. Two moles of product compared to three moles of reactants
  2. (To get more product, pressure should be increased) However it is expensive and unnecessary because the equilibrium is already on the right
  3. 1 Atmosphere is used
41
Q

What catalyst is used in the contact process?

A

Vanadium pentoxide catalyst

42
Q

What happens to strong acids in water?

A

They ionise completely = lots of H+ ions released

HCl ?> H+ + Cl?

43
Q

What happens to weak acids in water?

A

They don’t fully ionise = only small numbers of H+ ions are released

CH(3)OOH H+ + CH(3)OO?

44
Q

What is the pH of an acid/alkali a measure of?

A

The concentration of H+ ions

45
Q

How can the pH of an acid/alkali be measured?

A

With a pH meter or universal indicator paper

46
Q

What is the difference between strength and concentration of acids?

A 
Strength = tells you what proportion of the acid molecules ionise in water
Concentration = how many moles of acid there are in a litre
47
Q

Why are strong acids better electrical conductors than weak acids?

A

Weak acids have a lower number of ions and the ions are what carries the charge through acid solutions as they move

Chemistry (8 decks)

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