C3+C8 - Quantitative Chemistry+chemical analysis

Question 1

Compounds have a relative formula mass - mR

Answer 1

All relative atomic masses of all atoms in molecular formula added together 
E.g MgCl2 has a Mr 
Look at relative atomic masses Ar
Ar of Mg24 Ar of Cl 35.5 
Add up 24 +(2x 35.5) = 95

Question 2

Formular for percentage mass of elements in a compound

Answer 2

Percentage mass of element in a compound = (Ar x number of atoms of that element/ Mr of compound) x 100

Question 3

What are moles

Answer 3

Name given to an amount of a substance

Question 4

What’s the Avogadro constant

Answer 4

6.02 x 10^23

Question 5

What is one mole of any substance

Answer 5

One mole of any substance is just an amount of substance that contains an Avogadro number of particles. Particles could be atoms, molecules, ions or electrons

Question 6

What will one mole of atoms or molecules of any substance have

Answer 6

One mole of atoms or molecules of any substance will have a mass in grams equal to the relative formula mass for that substance
E.g carbon Ar of 12 - one mole of carbon weighs 12g

Question 7

Formula for moles

Answer 7

Number of moles = mass in g(of element or compound)/Mr(of element or compound)

Question 8

What is meant by mass is conserved in a chemical reaction

Answer 8

No atoms destroyed or changed

Means there’s the same number and typed of atom on each side of the equation > no mass loss or gained

Question 9

Why might mass increase during a chemical reaction

Answer 9

If mass increases it could be because one of the reactants is a gas that’s found it air like oxygen. And all products are solids, liquids or gases.
Before reaction - gas floating in air - not contained in the reaction vessel so you can’t account for its mass
When gas reacts to form part of product, becomes contain inside reaction vessel > total mass inside vessel increases

Question 10

What happens if mass decreases during a chemical reaction

Answer 10

If mass decreases, one of products is a gas and all reactants are solids, liquids or aqueous
Before reaction - all in contained vessel
If vessel isn’t enclosed, gas can escape from vessel as its formed. No longer contained in vessel > can’t account for mass so mass decreases

Question 11

What’s the big number in front of formulas

Answer 11

Big number in front of formulas tells you is many moles of each substance takes part or is formed during the reaction

Question 12

How do you work out the balanced symbol equation if you know the masses of reactants and products

Answer 12

1. Divide mass of each substance by RFM to find moles
2. Divide no of moles of each substance by smallest number of moles in reaction
3. If any numbers aren’t whole, multiply all numbers by same amount so they’re whole
4. Write Balanced Symbol equation with numbers

Question 13

When does a reaction stop

Answer 13

When one reactant is used up

Question 14

Process of a reaction stopping

Answer 14

1. Reaction stops when all of one reactant is used up. Any other reactants are in excess - usually added in excess so the one reactant is used up.
2. Reactant that is used up is the limiting reactant. - limits amount of product formed
3. Amount of product formed Is directly proportional to the amount of limiting reactant

Question 15

How to find the mass of product formed by using mass of limiting reactant and the balanced reaction equation

Answer 15

1. Write balanced equation
2. Work out relative formula masses of reactant and product you want
3. Find out how many moles there are in a substance you want to know the mass of
4. Use balanced equation to work out moles of other substances - moles of product
5. Use moles to calculate mass

Question 16

What is concentration

Answer 16

A measure of how crowded things are
Amount of substance (mass or moles) in a certain volume of a solution is called a concentration
More solute there is in a given Volume - more concentrated the solution
Concentration measured in g/dm3

Question 17

Equation for concentration.

Answer 17

Concentration = mass of solute/volume of solvent

Question 18

What is a pure substances

Answer 18

Something that only contains one compound or element throughout - not mixed with anything else

Question 19

How does the boiling/melting point tell you how pure a substance is

Answer 19

A chemically pure substance will melt/boil at a specific point

Test purity of sample by measure its point and comparing it to point of pure substances - close the value, the outer the substance
Impurities will Lower the melting point and increase melting range and will increase the boiling point and may result in sample boiling at a range of temperatures

Question 20

What are formulations

Answer 20

They are mixtures with exact amounts of components

Question 21

What are made by following a formula

Answer 21

Useful mixtures with precise purpose - each component in a formula is a measured quantitive and contributes to properties of formulation

Question 22

Example of formulation e.g paint

Answer 22

Paint contains
Pigment - gives paint colour
Solvent - dissolves other components and alters viscosity
Binder(resin) - forms film to hold pigment

Question 23

Why are formulations important for pills

Answer 23

Make sure it delivers the drug to the right part of the body at the right concentration and has enough shell life

Question 24

Test for chlorine gas

Answer 24

Bleached damp litmus paper, turning it white

Question 25

Test for oxygen

Answer 25

Oxygen will relight a glowing splint

Question 26

Test for carbon dioxide

Answer 26

Bubbling/shaking CO2 through aqueous solution of calcium hydroxide (limewater) will turn it cloudy

Question 27

Test for hydrogen

Answer 27

Splint will burn with a squeaky pop

Question 28

Two phases of paper chromatography

Answer 28

Mobile Phase - where molecules can move - liquid or gas
Stationary phase - molecules can’t move - solid or really thick liquid
Constantly move between phases - equilibrium between the two phases

Question 29

Mobile phase moves through the….

Answer 29

Stationary phase and anything dissolved in the mobile phase moves with it - how quick it moves depends on how it’s distributed between two phases

Question 30

What happens if solvent spends more time in the mobile phase

Answer 30

Solvent will move further

Question 31

Components in mixture will normal separate through what phase

Answer 31

Through stationary phase

Question 32

What’s a pure substance in paper chromatography

Answer 32

Only one spot

Question 33

In paper chromatography what is each phase

Answer 33

Mobile - the solvent

Stationary - the paper

Question 34

Time of molecules in each phase depends on…

Answer 34

How soluble they are in solvent
How attracted they are to the paper
Higher solubility and less attracted molecules spend more time I’m mobile phase - travel further up

Question 35

What is the rf

Answer 35

Ratio between distance travelled by solute and distance travelled by solvent

Question 36

Further through stationary phase =

Answer 36

Larger Rf

Question 37

Equation for Rf

Answer 37

Rf = distance travelled by substance/distance travelled by solvent

Substance distance = distance from baseline to colour spot
Solvent distance = distance from baseline to solvent front

Question 38

Why is paper chromatography carried out

Answer 38

To see if a specific substance is in a mixture