CHEMISTRY, C3

Question 1

Why are moles useful?

Answer 1

Atoms are too small to weigh individually so it’s easier to weigh a mole of something

Question 2

What is a mole?

Answer 2

A unit to measure the amount of a chemical we have

Question 3

What is the equation for the number of moles in a sample?

Answer 3

Mass of the substance/Mr

Question 4

What is theoretical yield?

Answer 4

The maximum possible mass of a product that can be made in a chemical reaction.

Question 5

What is the equation for percentage yield?

Answer 5

Actual yield produced/Theoretical yield of product x100

Question 6

Equation for percentage of atom economy?

Answer 6

Mr of the desired products / Mr of all reactants x100

Question 7

What is titration?

Answer 7

A technique that can be used to find out the concentration of an acid or an alkali.

Question 8

How can uncertainty be measured and how do you work it out?

Answer 8

By considering the resolution of the scientific equipment being used and from the range of the set of data. It’s the range/2

Question 9

What is Avogrado’s number?

Answer 9

6.02 x10 to the power of 23, number of particles in a mole.

Question 10

What happens when doing chemical calculations if the range gets larger?

Answer 10

More chance of error

Question 11

What are the tools needed in a titration practical?

Answer 11

pipette, burette, safety pipette filler, conical flask

Question 12

What is thermal decomposition?

Answer 12

A chemical reaction that happens when a compound is broken down when heated.

Question 13

What is the law of conservation of mass?

Answer 13

Matter can not be created or destroyed no matter how they are arranged.

Question 14

What is the equation for the concentration of a solution?

Answer 14

The mass of a substance (g)/ The volume of the solvent dm cubed

Question 15

What is the equation for working out moles of a gas?

Answer 15

Volume/molar gas volume (Vm)

Question 16

Why can we never have 100% yield in a reaction?

Answer 16

Other unexpected reactions can occur that don’t produce the desired product and sometimes not all of the reactants are used in the reaction.

Question 17

What is atom economy?

Answer 17

A measure of how many of the reactant atoms form a desired product.

Question 18

What are the preparation steps before doing a titration practical?

Answer 18

1. pipette should be rinsed with deionised water.
   2.Safety pipette filler is used to draw up the solution until bottom of menicis is on line then poured into conical flask.
   3.Burette is rinsed and then filled with solution ensuring the jet is filled.

Question 19

What is the method for the titration practical.

Answer 19

1. Use the pipette and pipette filler to add the sodium hydroxide to conical flask.
2. Add a few drops of indicator and put conical flask on white tile.
3. Fill burette with hydrochloric acid and note reading.
4. Add acid from burette to the conical flask and mix it.
5. Stop adding acid when the indicator changes colour and then repeat the steps until the concordant titres.

Question 20

What is the symbols for relative formula mass and relative atomic mass?

Answer 20

Relative formula mass - Mr
Relative atomic mass - Ar

Question 21

How do you calculate relative formula mass?

Answer 21

1. Work out how many atoms of each element there are in the chemical formula.
2. Add together the Ar values for all the atoms of each element present.
   For example, the formula for carbon dioxide is CO2. It consists of one carbon atom (Ar = 12) and two oxygen atoms (Ar = 16):

Mr of CO2 = 12 + 16 + 16 = 44

Question 22

True or false? No substances can leave or enter in a closed system?

Answer 22

True

Question 23

What has to happen for a solution to form?

Answer 23

Forms when a solute dissolves in a solvent.

Question 24

What’s the calculation for the mass of a solute?

Answer 24

Concentration in g/dm cubed × volume in dm cubed

Question 25

What are 2 ways that the concentration of a solution can be changed?

Answer 25

- Concentration can be increased by dissolving more solute in a given volume of solution. - Concentration can be increased by allowing some of the solvent to evaporate

Question 26

What's the equation for the number of particles in a substance?

Answer 26

Number of particles = Avogadro constant × the amount of substance in mol

Question 27

What's the equation for calculating masses of different substances?

Answer 27

relative formula mass × Moles

Question 28

Calculate the amount of carbon atoms in 6.0 g of carbon. (Ar of C = 12) Amount = Mass/Ar

Answer 28

6 divided by 12 = 0.5 mol

Question 29

In the reaction shown by the equation below, what mass of nitrogen, N2, is needed to make 120 g of nitrogen monoxide, NO? (Mr of NO = 30 and Mr of N2 = 28) N2(g) + O2(g) → 2NO(g)

Answer 29

120/30 = 4.0 mol 1 mol of N2 makes 2 mol of NO. This means that 2 mol of N2 makes 4.0 mol of NO. Mass of 2 mol of N2 = 2 × 28 = 56 g

Question 30

100 cm3 of dilute hydrochloric acid contains 0.02 mol of dissolved hydrogen chloride. Calculate the concentration of the acid in mol/dm3?

Answer 30

Volume of acid = 100 ÷ 1000 = 0.1 dm3 Concentration of acid = 0.02 mol ÷ 0.1 dm3 = 0.2 mol/dm3

Question 31

True or false? No atoms are gained or lost in a chemical reaction?

Answer 31

True

Question 32

What are some of the factors that a reaction pathway depends on?

Answer 32

- Percentage yield - Atom economy - Rate of reaction - Equilibrium position - Usefulness of by-products

Question 33

What is the molar volume?

Answer 33

The volume occupied by one mole of any gas, at room temperature and pressure

Question 34

Calculate the amount of helium that occupies 36 dm3 at room temperature and pressure. (Molar volume = 24 dm3) Show answer

Answer 34

Amount in mol = volume/molar volume 36 divided by 24 = 1.5 mol