3:quantitive chemistry

Question 1

what are chemical amounts measured in?

Answer 1

moles

Question 2

what is a mole?

Answer 2

One mole of a substance contains an Avogadro number of particles . One mole of a substance contains the same number of the stated particles, atoms, molecules or ions as one mole of any other substance.

Question 3

what is the value of the Avogadro constant

Answer 3

6.02 x 10^23

Question 4

iron has an R.A.M of 56,how much does one mole of iron weigh?

Answer 4

56g

Question 5

what does the law of conservation of mass state?

Answer 5

during a chemical reaction,no atoms are made or destroyed so the mads lf products is the same as the mass of the reactants

Question 6

what is the relative formula mass(Mr)?

Answer 6

the Mr of a compound is all the relative atomic masses of the atoms added together

Question 7

conservation of mass and Mr

Answer 7

Mr of the reactants and Mr of products show how mass is conserved.the Mr of reactants and Mr of the products is the same

Question 8

why might it seem like mass has increased in a reaction?

Answer 8

most likely because one or more reactants are gas found in air and the products are solids,liquids or aqueous

before the reaction gas is floating around in the air but its not in the reaction vessel so its mass ca’t be accounted for.When the gas reacts to from part of the product,the particles are then contained in the reaction vessel and the total mass of the products increase

Question 9

why might it seem like mass has decreased in a reaction?

Answer 9

one product is gas and all the reactants are solids ,liquids or aqueous

before the reaction all reactants are contained in the reaction vessel but if the vessel isn’t enclosed then the gas products can escape from as it is formed.Gas expands to fill the container its in so if a vessel isn’t sealed the gas escapes into the air.As it is not in the vessel,its mass can’t be accounted for and the mass of the reactants decrease

Question 10

what do gas particles try to do in their container?

Answer 10

fill the container its in.

Question 11

conservation of mass and equations

Answer 11

chemical reactions can be represented by equations which are balanced in terms of number of atoms on both sides

Question 12

how to work out the balanced symbol equation for a reaction if you know the masses of the reactants and products?[4]

Answer 12

1. divide mass of each substance by relative formula mass to find mes
2. divide number of moles of each by smallest number of moles in reaction
3. multiply all numbers by same amount if one number isn’t whole
4. write balanced equation by putting these numbers in front of the symbol

Question 13

what is a limiting reactant?

Answer 13

in a chemical reaction involving two reactants it is common to use an excess of one reactant to ensure that all of the other reactant is used up.The reactant that is completely used up is the limiting reactant(limits amount of product formed)

Question 14

limiting reactant and product?

Answer 14

amount of limiting reactant is directly proportional to amount of limiting reactant.(so if in one reaction 3g of the limiting reactant was used but in a different reaction 3x as much of the limiting reactant was used,the amount of product formed would also go up by 3x)

Question 15

calculating the mass of a product using the mass of the limiting reactant[5]

Answer 15

1. write out the balanced equation
2. work out the relative formula mass of the limiting reactant and product you want
3. work out moles of limiting reactant(using moles equation)
4. use balanced symbol equation to work out number of moles for the product (so if the reactant:product was at a 1:2 ratio then the product would have double the number of moles)
5. calculate mass(using rearranged moles equation)

Question 16

how much volume would 2 moles of oxygen take up if chlorine with the same number of moles took up 50dm^3?

Answer 16

50dm^3 because at the same temper and pressure,equal numbers of moles of any gas will occupy the same volume

Question 17

how would you find the volume of gas from an equation?

Answer 17

look at the molar ration of the gas of the balanced equation(eg reactant:product is 1:2 so multiply the volume of the gas reactant by 2)

Question 18

what is concentration?

Answer 18

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

Question 19

how would you convert cm^3 into dm^3?

Answer 19

divide the dm^3 amount by 1000

Question 20

mass of solute in a given volume

Answer 20

the greater the mass of a solute,the higher the concentration (so if you dissolve more of a solute into a solution,the concentration will increase but if you increase the volume w/o increasing amount of solute,concentration decreases)

Question 21

how to calculate uncertainty[3]

Answer 21

1. calculate mean volume
2. divide range(highest result-lowest result)by 2 to find uncertainty

3.write mean ± uncertainty unit

Question 22

how would you convert concentration in mol/dm^3 into concentration g/dm^3?

Answer 22

multiply the concentration by the relative formula mass

Question 23

what is atom economy?

Answer 23

a measure of the amount of starting materials that end up as useful products

Question 24

what would the atom economy be if you only have one product?

Answer 24

100% because all of the reactants end up in the useful products

Question 25

what are the economic advantages of a high atom economy?[2]

Answer 25

1. reactions with low atom economies produce more waste 2. need more raw materials to produce a certain amount of a product which can be expensive to but and expensive to remove overall,low atom economies usually aren’t profitable

Question 26

what are the environmental advantages of high atom economy?

Answer 26

1. use fewer raw materials,many of which will run out eventually so it’d be better to try and and make them last 2. produce less waste which is good as waste chemicals are often harmful high atom economy processes are more sustainable

Question 27

what is the theoretical yield?

Answer 27

amount you would get if all reactants formed desired products and none of the products were lost

Question 28

what is yield?

Answer 28

amount of product you obtain in a reaction

Question 29

what is the percentage yield?

Answer 29

comparison between theoretical yield and the yield

Question 30

what does a 0% yield mean?

Answer 30

no reactants were converted into products

Question 31

why are percentage yield never 100%[3]

Answer 31

1. reaction is reversible 2. some product is lost when separated from reaction mixture 3. some reactants may react in ways different than expected reaction(eg. side reactions such as reactant reacting with gases in the air)

Question 32

what factors are considered when choosing a particular reaction pathway to produce a specific product to make sure the reaction is economically and sustainable?[5]

Answer 32

1. atom economy 2. yield 3. rate 4. equilibrium position 5. usefulness of by-products

Question 33

why is atom economy considered when choosing which reaction to use to make a specific substance an industrial scale?

Answer 33

reactions with higher stomach economies produce less waste and need less raw materials so reactions are cheaper and more sustainable

Question 34

why is yield considered when choosing which reaction to use to make a specific substance an industrial scale?

Answer 34

high percentage yield means less reactant wasted so reactions are cheaper and more sustainable as less waste is made and less raw materials used

Question 35

why is rate considered when choosing which reaction to use to make a specific substance an industrial scale?

Answer 35

rate of a reaction measures how quickly reactants reacts to form product.You want products to be made at a reasonable rate

Question 36

why is equilibrium position considered when choosing which reaction to use to make a specific substance an industrial scale?

Answer 36

being able to control equilibrium position to maximise amount of product is important for making the process profitable.

Question 37

where should the equilibrium position of a reversible reaction used in industry be?

Answer 37

should have an equilibrium position where amount of products formed is high and amount of reactant left is low

Question 38

why is usefulness of by-product considered when choosing which reaction to use to make a specific substance an industrial scale?

Answer 38

by choosing reactions that form useful by-products(as well as intended product)reduces waste