Amount Of Substance

Question 1

How many particles does one mole contain ?

Answer 1

6.02 x 10^23

Question 2

Formula for converting between no. Of particles and no. Of moles

Answer 2

Number of particles = number of moles x avagadro’s constant

Question 3

What is the moles , mass and mr equation

Answer 3

Moles = mass/mr

Question 4

Important conversions

Answer 4

1 ton = 1000000g
1kg = 1000g (x 1000)
1mg = 0.001g ( divide by 1000)

Question 5

What are the three steps to moles mass and mr equation

Answer 5

Step 1 : find number of moles of the compound which the mass is given for
Step 2 : determine ratio of number of moles between the compound which we had the mass for and the compound that we need to find the mass for
Step 3 : find the mass of the compound using the number of moles
Mass = mr x mole

Question 6

What are the steps to a moles, mass and mr question when we are given the mass of both reactants

Answer 6

Step 1 : calculate the number of moles for each compound (eg 3.75 and 0.35)
Step 2 : pick one compound and find the ratio of the other to see which one is in excess and which one is limiting
(Eg if 0.35 and ratio 1:2 then we only need 0.70 but we have 3.75)
The limiting one is the one we use
Find the ratio of the limiting reactant and the product we need to find
Step 3 : find the mass of the product

Question 7

What formula do you use to calculate no. Of moles from concentration ?

Answer 7

Moles = concentration x volume

Question 8

What is concentration equation

Answer 8

Conc = moles/vol

Question 9

Important conversions for concentration equation

Answer 9

Cm 3 to dm3 = divide by 1000
Dm 3 to m 3 = divide by 1000
Cm 3 to m3 = divide by 1000000

Question 10

Steps to calculating normal concentration equation

Answer 10

Step 1 : Use equation to find number of moles of given reactant
Using the concentration of it and the volume
Step 2: use ratio to find number of moles of next reactant for product
Step 3 : find conc using equation

Question 11

Steps to find concentration when given the mass of a reactant

Answer 11

Step 1 First use moles = mass/ mr for the given reactants
Step 2 : ratio to find number of moles for other compound
Step 3 : find conc

Question 12

How do you use the concentration equation in a question where you are given the moles of one reactant and the vol and conc of reactant and you need to find the product

Answer 12

Step 1 : find the number of moles of the one where you are given the concentration and the volume
Step 2 : find the ratio between this and the compound with the number of moles given.
Find out which one is in excess and which one is limiting
The limiting one should be used in the ratio with the compound you are trying to find

Question 13

ZnO + 2HCl -> ZnCl2 + H20
ZnO = 0.0830 moles
2HCl = 100cm3 and 1.20 mol dm-3
Find the mass of ZnCl2

Answer 13

Step 1 : find moles of both 
Already given moles of ZnO 
Moles of HCl = conc x vol = 1.20 x 100/1000=0.12
Step 2 : ratio of HCl to ZnO 
2:1 so 0.12/2 = 0.06 0.06 is less than ZnO so HCl limiting 
Step 2.5 : ratio of HCl and ZnCl2 = 2:1 
Moles of ZnCl2 = 0.06 
Step 3 : mass = mr x mol

Question 14

What is the molecular formula ?

Answer 14

The average masses of atoms in formula compared to 1/12th mass of an atom of carbon 12

Question 15

What is a standard (volumetric ) solution ?

Answer 15

A solution that you know the exact concentration of

Question 16

What does the making of a standard solution involve ?

Answer 16

Involves dissolving a known amount of solid in known amount of water to create known concentration molecules

Question 17

Describe how would you make 250 cm3 of 2.00 mol dm-3 solution

Answer 17

1. 0.5 moles of sodium hydroxide needed and 20.0g of sodium hydroxide needed
2. place weighing boat on digital balance and weigh out mass of solid
3. Tip it into beaker
4. reweigh boat
5. Subtract mass of boat from mass of boat and solid together = find precise mass of solid. (Record difference).
6. Add distilled water to beaker (eg 100dm3) and stir until sodium hydroxide dissolved
7. Pour solution into 250 cm3 volumetric flask using funnel
8. Rinse beaker , stirring rod with distilled water and add washing to flask
9. Add solvent to correct volume until graduation line then drop by drop until bottom of meniscus reaches the line.
10. Invert flask several times to make sure it is mixed and a uniform solution

Question 18

Why do you rinse the beaker and stirring rod with distilled water and add that to flask

Answer 18

Makes sure no solute clings to the beaker or rod

Question 19

What do titrations allow you to do ?

Answer 19

Allow to find out exactly the volume of acid needed to neutralise quantity of alkali

Question 20

What is the method for titration

Answer 20

1. Use Pipette to measure 250 cm3 set volume of solution/ solid you want to find concentration of into conical flask
   2.add few drops of indicator
2. Fill Burette with standard solution of acid HCl) mention what concentration the HCL or acid is
3. Use funnel to pour acid into burette - done at eye level
4. Do rough titration to get idea of end point by adding acid to alkali using burette and give flasks regular swirls
5. Do accurate titaration
   Take initial reading of acid
   Run acid with 2cm3 of end point
   Add acid drop wise until end point reached

Question 21

How do you find volume of titre

Answer 21

Final reading - initial reading

Question 22

Until when should you repeat the titration

Answer 22

Until you have 3 concordat results

Question 23

What is a anomalous result

Answer 23

A result that it more or less than 5 away from the other results

Question 24

What kind of indicators should be used ?

Answer 24

Ones that change colour quickly so have a small ph range so we know exactly when the reaction has ended

Question 25

Why is it important to wash/ rinse the inside of flask and why does it not affect the titre value

Answer 25

So that all the solution reacts with each other and is in the flask Water does not change number of moles in either reactant

Question 26

Why is it essential to remove the funnel after being used to fill the burette

Answer 26

Droplet from funnel could enter the burette and effect the readings

Question 27

What is the source of error in using a burette

Answer 27

Air bubbles

Question 28

What is the effect of the air bubble

Answer 28

The value of the titre would be higher

Question 29

Why is a conical flask used rather than beaker

Answer 29

Less chance of losing liquid in swirling

Question 30

How do you calculate % uncertainty

Answer 30

Error/ measurement x 100

Question 31

What two things do you have to be careful about when it comes to uncertainty ?

Answer 31

1. How much the equipment has been used (if twice then error x 2) 2. Make sure it is a measurement not a reading ( might have to find the difference in readings for the measurement)

Question 32

How can you reduce uncertainty ?

Answer 32

Reducing the error (eg more accurate balance or apparatus with greater resolution) Decrease concentration of solution in burette to increase volume measurement

Question 33

What do burettes measure and let you do ?

Answer 33

Measure different volumes and lets you add solution drop by drop

Question 34

What do pipettes measure

Answer 34

Only one volume of solution

Question 35

If there is only two results what should you do ?

Answer 35

Do further titrations for concordant results

Question 36

How is the method for standard solution accurate

Answer 36

1. The precise mass of solid is obtained by subtracting mass of boat from mass of boat and solid together 2. Wash the rod and add washings to the beaker 3. Ensure bottom of meniscus reaches is on graduation Lind

Question 37

What is the ideal gas equation

Answer 37

PV=nRT

Question 38

What are all the units of the ideal gas equation

Answer 38

``` P= pressure (Pa) V= volume (m3) N= number of moles T= temperature (k) ```

Question 39

Volume: Dm3 to m3 Cm3 to m3

Answer 39

Dm3 to m3 = divide by 1000 | Cm3 to m3 = divide by 1000000

Question 40

Pressure : Kpa to pa Map to pa Atmosphere

Answer 40

Kpa- pa X 1000 Mpa- pa X100000 Atmosphere - x101325

Question 41

How do you convert Celsius to K

Answer 41

C + 273

Question 42

What is the rule for volume of gases

Answer 42

At room temperature and pressure 1 mol of any gas occupies 24 dm3

Question 43

How do you find the mass of single atom in a element

Answer 43

Mr/ Avogadro constant

Question 44

Ideal gas equation rearranged

Answer 44

For number of moles = Pv/rt Temperature = pv/ nr Volume = nRt/p Pressure = nRt/V

Question 45

What is the formula for atom economy

Answer 45

Mass of wanted product from equation / total mass

Question 46

What is the formula for percentage yield

Answer 46

Mass of product formed / maximum theoretical mass of product

Question 47

Why do companies in the chemical industry try to use processes with high atom economies

Answer 47

Better for environment so they produce less waste More efficient use of raw materials so more sustainable Less expensive

Question 48

In a titration a burette with an uncertainty of 0.05cm3 is used. Initial reading = 50cm3. The final reading 28.8cm3

Answer 48

50.0-28.8=21.1 0.05 Two burette readings = 0.05 + 0.05 = 0.01cm3 0.1/21.2 x 100= 0.5 %

Question 49

Why do we re weigh the boat ?

Answer 49

It may contain traces of solid

Question 50

If a question already has the yield given how do you answer the question (theoretical mass ) step by step

Answer 50

Step 1. Find number of moles of reactant. Step 2. Ratio to find number of moles of product Step 3 number of moles is the certain yield for example 62% but we need the theoretical mass (100%) Step 4: divide number of moles by percentage then multiply by 100 Step 5: mass

Question 51

How do you find the mass of the percentage yield when just given the percentage and mass of reactant but not the mass of percentage Normal question : 510g actually made This question : 90% percentage yield

Answer 51

Step 1: find moles Step 2 : ratio Step 3: mass This mass is the 100% so we need the specific percentage so mass should be multiplied by the percentage yield needed/100

Question 52

If a question asks you to do a titration of a reaction but has not given a certain mass of a solid or volume of and concentration of acid what should you do

Answer 52

For mass : moles, ratio mass Moles would be found through concentration equation For volume and concentration = rearrange concentration equation to find what you are looking for

Question 53

How do you find the molecular mass from formula mass and empirical formula

Answer 53

Step 1 : write down empirical formula and mr (CH2)(mr=42) Step 2 : find the formula mass which is just adding the Ars together Fm -12+2=14 Step 3 : find multiplier by dividing mr given by formula mass 42/14=3 Step 4 : multiplier x empirical formula 3xCH2=C3H6

Question 54

How do you find the empirical formula

Answer 54

1) write out each element 2) write all masses or mass percentages of each element 3) divide mass/% by ar 4) divide smallest number by every other number to give whole number ratio

Question 55

How do you find a mass of certain element if just given compound for example CO2 (just want to find carbon)

Answer 55

First find total mass of compound = should always be given!! Do mr of element divided by total mr of compound and multiply by total mass to give percentage of that specific element Eg mass = 1.10g 12/44 x 1.10 = 0.3 12 = mr of just carbon 44= mr of co2 0.3g of carbon

Question 56

What should you be careful about when calculating empirical formula of a compound with Same element reacting with different things

Answer 56

The empirical formula of the certain element is split between every time that element reacts with something Eg if it says (nh3 )3 at the start but (nh4)x at the end and empirical formula of n is 7 There is already 3 ns being used up so the x would be - 7-3=4 x=4

Question 57

How do you convert from mol dm3 to g dm3

Answer 57

Multipliy by mr

Question 58

How can you check if all the water has been removed

Answer 58

Reheat until mass hasn’t changed

Question 59

Empirical formula question

Answer 59

1. Record mass of dish 2. Add known mass of hydrated metal Sulfate 3. heat over a Bunsen burner until mass has reached a constant mass - meaning all the water has been lost and the mass is not changing 4. Record mass of evaporating dish and contents and use this to calculate the mass of the anhydrous salt and the mass of water lost 5. Divide by mr and then smallest

Question 60

How do you you find out the mass of the water and solid ?

Answer 60

mass of evaporating dish and solid before heating - mass of empty evaporating basin = about of solid before heating Mass of evaporating basin before heating - mass of evaporating basin and solid after heating = amount of water Amount of solid before heating - amount of water = amount of solid after heating