Chemical calculations (unfinished)

Question 1

What is a mole?

Answer 1

the relative formula mass of a substance in grams

Question 2

What is Avogadro’s constant?

Answer 2

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

Question 3

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

Answer 3

Mass/Mr or Mass/Ar

Question 4

How are masses of atoms measured?

Answer 4

They are compared with the mass of carbon-12

Question 5

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

Answer 5

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

Question 6

H2 + Cl2 = ?

Answer 6

2HCl

Question 7

What can balanced symbol equations be used for?

Answer 7

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

Question 8

What is the limiting reactant?

Answer 8

The reactant that gets used up first in a reaction

Question 9

What reactant is not in excess?

Answer 9

The limiting reactant

Question 10

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

Answer 10

The limiting reactant

Question 11

How do you calculate percentage yield?

Answer 11

actual yield/theoretical yield x 100

Question 12

What is theoretical yield?

Answer 12

The maximum yield that could be obtained if all atoms reacted

Question 13

What factors affect percentage yield?

Answer 13

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)

Question 14

Why do you want an economical chemical reaction?

Answer 14

-Less waste

-More product for the same reactants

-More profit

-Less pollution

Question 15

How do you create an economical chemical reaction?

Answer 15

• Waste as little energy as possible
• Waste as little raw materials as possible
• Conserve limited resources

Question 16

What is the atom economy?

Answer 16

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.

Question 17

What ideally happens with by-products of chemical reactions?

Answer 17

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

Question 18

How do you calculate atom economy?

Answer 18

Atom Economy =

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

Question 19

What is the ideal atom economy?

Answer 19

100%

Question 20

What is concentration?

Answer 20

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

Question 21

What is a solute?

Answer 21

A substance that is dissolved in a solution.

Question 22

What is a solvent?

Answer 22

The substance that dissolves the solute

Question 23

What is a solution?

Answer 23

A mixture of solute and solvent

Question 24

How much is a decimetre cubed (dm^3)

Answer 24

1000cm^3

Question 25

What is concentration of a solution measured in?

Answer 25

g/dm^3

Question 26

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

Answer 26

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

Question 27

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

Answer 27

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

Question 28

How do you increase the concentration of a solution?

Answer 28

-Add more solute -Remove solvent

Question 29

What happens when an acid and alkali react together?

Answer 29

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

Question 30

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

Answer 30

The product will be acidic

Question 31

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

Answer 31

The end point

Question 32

How can you judge when the end point is reached?

Answer 32

Using an acid/base indicator

Question 33

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

Answer 33

Titre

Question 34

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

Answer 34

Concordant

Question 35

What instrument is used to measure the solution added?

Answer 35

Burette

Question 36

What is titration?

Answer 36

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

Question 37

How do you work out concentration from titrations?

Answer 37

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

Question 38

What is the meniscus?

Answer 38

The curved upper surface of a liquid in a tube.

Question 39

What safety precautions must be taken?

Answer 39

- Goggles - Stay stood up - Wear protective clothing - (Substances may be corrosive and irritants)

Question 40

Where do you put the solution with an unknown concentration?

Answer 40

The conical flask

Question 41

Where do you put the solution with the known concentration?

Answer 41

The burette

Question 42

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

Answer 42

Multiply the mol/dm^3 by the formula mass

Question 43

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

Answer 43

24dm^3

Question 44

How do you work out number of moles of gas

Answer 44

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

Question 45

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

Answer 45

Calculating the volume of gaseous reactants or products

Question 46

(page 79)