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Chemistry Paper 1. > Quantitative Chemistry. > Flashcards

Quantitative Chemistry. Flashcards

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1
Q

What is relative formula mass?

A

Mr Relative atomic masses of all atoms in molecular formula added together.

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2
Q

What is the Ar?

A

Single relative atomic mass of an element it is just the mass number. Which is the top number.

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3
Q

How to calculate the percentage mass if an element in a compound?

A

Ar x number of atoms of that element / mr of compound X100

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4
Q

Define mole.

A

Name given to amount of a substance.

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5
Q

What is one mole?

A

Amount of that substance that contains Avogadro number of particles so 6.02x10^23 the particles could be atoms molecules ions or electrons.

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6
Q

How to calculate the number of moles?

A

Mass in g / mr

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7
Q

Give the triangle for moles mass and mr

A

Mass at the top Number of moles Mr

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8
Q

What happens during a chemical reaction?

A

No atoms are destroyed and no atoms are created. Do the same number and types of atoms on each side of a reaction equation. Because of this no mass is lost or gained so mass is conserved.

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9
Q

Explanation one to why mass changes in an unsealed reaction vessel during a reaction.

A

If mass increases it’s because one of reactants is a gas that’s found in the air like oxygen and all products are solids liquids or aqueous. Before reaction gas floats in air, it is not contained in reaction vessel, so you can’t account for its mass When gas reacts to form part of product it becomes contained inside reaction vessel. So total mass of stuff inside reaction vessels increases.

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10
Q

A example for explanation 1 of why mass changes.

A

Metal reacts with oxygen in an unsealed container mass will increase Mass of metal oxide produced equals total mass of metal and oxygen that reacted from the air.E

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11
Q

Explanation 2 of why mass changes.

A

If mass decreases it’s due to one of the products is a gas and all the reactants are solids liquids or aqueous. Before reaction all reactants are contained in the vessel. If vessel is not enclosed then the gas can escape from the reaction vessel as it’s formed. It’s no longer contained in the reaction vessel so you can’t account for it’s mass. -the total mass of inside the reaction vessel decreases.

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12
Q

Give an example of explanation two of why mass changes.

A

Metal carbonate decomposes thermally to form a metal oxide and carbon dioxide gas, the mass of reaction vessel will decrease if not sealed. But in reality the mass of metal oxide and carbon dioxide produced will equal mass of metal carbonate that decomposed. metal carbonate = metal oxide + carbon dioxide

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13
Q

How can you tell a reaction is occurring between magnesium and hydrochloric acid?

A

Bubbles of gas are given off.

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14
Q

Why does a reaction stop?

A

When all of one reactant is used up. Any other reactants are in excess. They are usually added in excess to make sure the other reactant is used up.

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15
Q

Define the limiting reactant.

A

the reactant that is used up in a reaction. As it limits the product formed.

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16
Q

What is directly proportional to the amount of produce formed?

A

Amount of limiting reactant. Ex: if you half the amount of limiting reactant the amount of product will be halved. Because if you add more reactant there will be more reactant particles to take part in the reaction so there are more product particles.

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17
Q

Give the steps to work out the mass of a product formed in a reaction by using mass of limiting reaction and balanced reaction equation?

A

1= Write out balanced equation 2= Work out relative formula mass (Mr) of reactant and product you want. 3= find out how many moles there are in the substance you know the mass of. 4= Use balanced equation to work out how many moles will be of other substances. 5= In this case that is how many moles of products will be made of this many moles of reactant 6=use number of moles to calculate mass

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18
Q

What is theoretical yield?

A

Masses you calculate as in pracrice you can never get 100% yield so the amount of product you get will be less than calculated.

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19
Q

What will ocupy the same volume?

A

At the same temperature and pressure, equal numbers of moles of any gas will occupy the same volume.

20
Q

How much volume does one mole of any gas occupy at 20 degrees celcius? (room temperature)

A

24dm cubed

21
Q

Give the formula to find out the volume of known mass of any gas at room temperature.

A

Volume of gas = mass of gas / Mr of gas x24 VG= dm cubed Mass of gas= g

22
Q

Define the term concentration.

A

The amount of a substance in a certain volume of a solution.

23
Q

What makes a more concentrated solution?

A

The more solute there is in a given volume.

24
Q

How would you calculate the concentration of a solution? for dm3

A

concentration = mass of solute / volume of solvent

concentration = g/dm cubed

mass of solute = g

volume of solvent = dm cubed

25
Q

How to calculate concentration if given in a mole.

A

concentration = number of moles of solute / volume of solvent

concentration= mol/dm3

number of moles in solute= mol

volume of solvent= dm3

26
Q

How would you calculate the mass of a solute in a solution?

A

mass = conc. x volume

27
Q

What do titration experiment allow you to do?

A

Find the volumes needed for two solutions to react completely

28
Q

Give the handy formula triangle for concentration

A

no of moles

conc. x volume

29
Q

How do you convert from mol/dm3 to g/dm3

A

mass = moles x Mr

30
Q

What is atom economy?

A

Or atom utilisation of a reaction tells you how much of the mass of the reactants is wasted when manufacturing a chemical and how much is a useful product.

31
Q

Give the formula for atom economy.

A

a e = relative formula mass of desired product / relative formula mass of all reactants x100

32
Q

What does 100% atom economy mean?

A

all the atoms in the reactants have been turned into useful products. The higher the atom economy the greener the process.

33
Q

Reactions with low atom economy uses what?

A

Resources used up very quickly.

The make lots of waste materials that have to be disposed of somehow

That tends to make these reactions unsustainable -raw materials will run out and waste has to go somewhere.

34
Q

Are low atom economy reactions profitable?

A

No, raw materials are expensive to buy and waste products can be expensive to remove and dispose of responisbly.

35
Q

Solution to low atom economy.

A

Find a use for waste products rather than throwing them away.

Often more than one way to make product you want so find a reaction which makes useful by products

36
Q

Describe reactions with the highest atom economy

A

They only have one product

Those reactions have an atom economy of 100%

The more products there are the lower the atom economy is

37
Q

When choosing which reaction to use to make a certain product which factors should be considered?

A

Yield

Rate of reaction

Position of equilibrium for reversible reactions

A reaction with low atom economy that produced useful by products may be used.

38
Q

What is yield?

A

The amount of product you get

39
Q

What does a higher yield mean?

A

The more products you started with

40
Q

Give the formula for percnetage yield.

A

%yield = mass of product actually made / maximum theoretical mass of product x100

mass of product actually made = g

maxiumum theoretical mass of product = g

41
Q

What is percentage yield always between?

A

0-100

100% yeild means you got all product you expected to get

0% means no reactants were converted into products

42
Q

Describe the percentage yield for industrial processes

A

High as posssible to reduce waste and reduce costs.

43
Q

Name the three reasons why we don’t get 100% yeild.

A

1= not all reactants react to make a product

2= there might be a side reaction

3= you lose some product when you seperate it from the reaction mixture.

44
Q

Describe why not all reactants react to make product gives you less than 100% yield.

A

in reversible reactions the products can turn back into reactants so yield will never be 100%

ex: haber process at the same time as reaction n2+3H2 = 2NH3 is occuring the reverse reaction 2NH3 = N2 + 3H2 is also happening.

So the first reaction never goes to completion so reactants don’t get used up

45
Q

How does side reactions affect percentage yield.

A

Reactants may react differently to how you expect.

Might react with gases in the air or impurities in the mixture so you form extra products other than ones you want

46
Q

How does losing some product when you separate it from th reaction mixture affect percentage yield.

A
  • When you filter liquid to remove solid particles you lose liquid or solid
  • If you want to keep liquid you lose the but that remains with solid and filter paper as they stay wet
  • If you want to keep solid some of it is left behind as you scrape it of filter paper.
  • You lose material when you transfer it from one contianer to another
  • Or left behind on inside surface of continer

Chemistry Paper 1. (5 decks)

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