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Chemistry > Chemical calculations (unfinished) > Flashcards

Chemical calculations (unfinished) Flashcards

1
Q

What is a mole?

A

the relative formula mass of a substance in grams

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2
Q

What is Avogadro’s constant?

A

6.022 x 10^23 /mol, is equal to the number of particles in 1 mole.

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3
Q

How do you calculate the number of moles in a substance?

A

Mass/Mr or Mass/Ar

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4
Q

How are masses of atoms measured?

A

They are compared with the mass of carbon-12

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5
Q

How do you work out relative formula mass of a compound?

A

Add up the relative atomic masses of all the atoms in the compound.

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6
Q

H2 + Cl2 = ?

A

2HCl

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7
Q

What can balanced symbol equations be used for?

A

To calculate the masses of reactants and products in a chemical reaction

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8
Q

What is the limiting reactant?

A

The reactant that gets used up first in a reaction

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9
Q

What reactant is not in excess?

A

The limiting reactant

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10
Q

What determines the amount of products made in a chemical reaction?

A

The limiting reactant

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11
Q

How do you calculate percentage yield?

A

actual yield/theoretical yield x 100

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12
Q

What is theoretical yield?

A

The maximum yield that could be obtained if all atoms reacted

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13
Q

What factors affect percentage yield?

A

1) Product lost during separation (e.g. filtration)

2) Side reactions

3) Incomplete reactions

4) Impure reactants

5) Inefficient reactions

6) Quantity of reactants (you can only make as much as your limiting reactant alloProduct lost during separation (e.g. filtration)

7) Product lost during separation (e.g. filtration)

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14
Q

Why do you want an economical chemical reaction?

A

-Less waste

-More product for the same reactants

-More profit

-Less pollution

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15
Q

How do you create an economical chemical reaction?

A
  • Waste as little energy as possible
  • Waste as little raw materials as possible
  • Conserve limited resources
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16
Q

What is the atom economy?

A

Atom economy is a measure of the proportion of reactant atoms that become part of the desired product (rather than by-products) in the balanced chemical equation.

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17
Q

What ideally happens with by-products of chemical reactions?

A

The by-products can be used for another purpose as they are an extra expense to throw away (especially hazardous waste)

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18
Q

How do you calculate atom economy?

A

Atom Economy =

(M/Ar of Desired product/M/Ar of reactants) x 100

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19
Q

What is the ideal atom economy?

A

100%

20
Q

What is concentration?

A

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

21
Q

What is a solute?

A

A substance that is dissolved in a solution.

22
Q

What is a solvent?

A

The substance that dissolves the solute

23
Q

What is a solution?

A

A mixture of solute and solvent

24
Q

How much is a decimetre cubed (dm^3)

A

1000cm^3

25
Q

What is concentration of a solution measured in?

A

g/dm^3

26
Q

How do you work out concentration with amount of solute (g) and volume of solution (dm^3)

A

Amount of solute (g) / Volume of solution (dm^3) = Concentration (g/dm^3)

27
Q

How do you work out concentration with amount of solute (g) and volume of solution (cm^3)

A

( Amount of solute (g) / Volume of solution (cm^3) ) x 1000 = Concentration (g/dm^3)

28
Q

How do you increase the concentration of a solution?

A

-Add more solute

-Remove solvent

29
Q

What happens when an acid and alkali react together?

A

They neutralise each other, forming a salt and water in the process.

30
Q

What will happen if acid is in excess in a mixture between a strong acid and a strong alkali.

A

The product will be acidic

31
Q

What is it called when the acid and alkali have completely reacted?

A

The end point

32
Q

How can you judge when the end point is reached?

A

Using an acid/base indicator

33
Q

What is the volume of the acid/alkali needed to neutralise the alkali/acid?

A

Titre

34
Q

What are titres that are within 0.1 cm3 of each other?

A

Concordant

35
Q

What instrument is used to measure the solution added?

A

Burette

36
Q

What is titration?

A

the process of adding a known amount of solution of known concentration to determine the concentration of another solution

37
Q

How do you work out concentration from titrations?

A

1) Measure a known volume of alkali into a volumetric pipette

2) Add a few drops of acid/base indicator to the solution and swirl

3) Fill a burette with a certain measurement of acid and write the measurement down

4) Release a certain amount of acid into the solution from the burette and swirl the solution

5) Repeat step 4 until the indicator changes colour

6) Record the volume of acid that has been mixed into the solution (titre)

7) Repeat the whole process 2 more times and discard anomalous results or keep going until you get 2 titres that are within 0.1cm^3 of each other (concordant results) then calculate the mean

8) Use these results to calculate the concentration of the alkali in mol/dm^3

38
Q

What is the meniscus?

A

The curved upper surface of a liquid in a tube.

39
Q

What safety precautions must be taken?

A
  • Goggles
  • Stay stood up
  • Wear protective clothing
  • (Substances may be corrosive and irritants)
40
Q

Where do you put the solution with an unknown concentration?

A

The conical flask

41
Q

Where do you put the solution with the known concentration?

A

The burette

42
Q

How do you convert from mol/dm^3 to g/dm^3

A

Multiply the mol/dm^3 by the formula mass

43
Q

What is the volume of 1 mole of any gas at room temperature?

A

24dm^3

44
Q

How do you work out number of moles of gas

A

volume of gas(dm^3)/24dm^3 or volume of gas(cm^3)/24000cm^3

45
Q

What can the molar gas volume and balanced symbol equations be used for?

A

Calculating the volume of gaseous reactants or products

46
Q

(page 79)

A

Chemistry (7 decks)

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