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Chemistry > Quantitive Chemistry > Flashcards

Quantitive Chemistry Flashcards

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1
Q

what is the relative formula mass?

A

sum of all the relativeatomic masses of the atoms in the molecular formula

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2
Q

how do you work out the percentage mass of an element in a compound?

A

Alittle r x number of atoms of that element / Mlittle r of compound x 100

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3
Q

what is Alittle r?

A

RAM

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4
Q

what is Mlittle r?

A

RFM

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5
Q

what is a balanced equation?

A

a symbol equation with the same number of atoms of each element on both sides

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6
Q

give the balanced equation of magnesium + oxygen.

A

2Mg + O2 > 2MgO

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7
Q

what is 1 mole equal to?

A

6.02x10^23 particles of a substance

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8
Q

what is avogadro’s constant?

A

6.02x10^23

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9
Q

how do you work out the number of moles?

A

mass in grams / RFM (Mlittle r)

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10
Q

what is the conservation of mass?

A

no atoms are created or destroyed in a chemical reaction, so the total masses of reactants and products are also the same.

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11
Q

why would you find a decrease in mass in an unsealed reaction vessel?

A

a gas is made during the reaction and escapes the vessel, so its mass is no longer accounted for

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12
Q

why would you find an increase in mass in an unsealed reaction vessel?

A

a gas from the air is a reactant, so its mass is added to the mass in the vessel

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13
Q

how can a balanced equation tell you the moles?

A

the number in the front is the number of moles.

Mg + 2HCl > MgCl + H
so theres 1 mole of Mg reacting with 2 moles of HCl

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14
Q

how do you balance an equation using masses?

A

divide mass by RFM to find the number of moles of each substance > divide each number of moles by the smallest number of moles > if results aren’t whole numbers, mulitply them by the same number so that they are whole > put these numbers in front of the chemical formulae.

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15
Q

what is a limiting reactant?

A

a reactant that gets completely used up in a reaction, so limits the amount of product formed.
all the other reactants are in excess

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16
Q

if you know the mass of the limiting reactant, how can you work out the mass of a product?

A

write the balanced equation for the reaction > divide the mass of the limiting reactant by the RFM to find the number of moles > use the balanced equation to find the number of moles of the product > multiply this number of moles by the RFM of the product to work out its mass.

17
Q

tell me about gases.

A

at the same temperature and pressure, one mole of gas will occupy the same volume.
at room temperature and pressure, one mole of any gas occupies 24 dm3

18
Q

what is room temperature and pressure?

A

20C and 1atm

19
Q

how do you work out the volume of gas?

A

volume of gas = mass / RFM x 24

20
Q

what is concentration?

A

amount of substance dissolved in a certain volume of solution

21
Q

what happens if you increase the amount of solute

A

concentration increases

22
Q

what happens if you increase the volume of solvent?

A

concentration decreases

23
Q

what are teh two ways to measure concentration?

A

1: mass of solute / volume of solvent = g/dm3
2: number of moles of solute / volume of solvent = mol/dm3

24
Q

how do you find an unknown concentration from the result of a titration?

A

multiply the konwn concentration by measured volume to work out the number of moles of reactant 1 > use reaction equation to work out how many moles of reactant 2 have reacted > divide number of moles of reactant 2 by its volume to get the unknown concentration

25
Q

what is reactant 1 of a titration?

A

measured volume, known concentration

26
Q

what is reactant 2 of a titration?

A

known volume, unknown concentration (+ indicator)

27
Q

what is atom economy?

A

also called atom utilisation
the percentage of the mass of reactants that ends up as useful products

28
Q

how do you calculate the atom economy?

A

total RFM of desired products / total RFM of all reactants x 100

29
Q

what are 3 advantages of using reactions with higher atom economies?

A

1: use up resources at a slower rate
2: don’t produce a lot of waste
3: more profitable

30
Q

what is yield?

A

the amount of product made in a reaction

31
Q

what is percentage yield?

A

a comparison of the amount of product you actually get (yield) with the maximum you could theoretically get

32
Q

how do you calculate percentage yield?

A

mass of products actually made / maximum theoretical mass of product x 100

33
Q

what does higher % yield mean?

A

less waste and lower costs

34
Q

what are 3 common reasons for less than 100% yield?

A

1: reaction is not complete - eg, its reversible
2: side reeactions use up some of the reactants or product
3: some product is lost when it’s separated from the reaction mixture

Chemistry (11 decks)

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