Flashcards in Amount Of Substance Deck (60)

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1

## How many particles does one mole contain ?

### 6.02 x 10^23

2

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

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

3

## What is the moles , mass and mr equation

### Moles = mass/mr

4

## Important conversions

###
1 ton = 1000000g

1kg = 1000g (x 1000)

1mg = 0.001g ( divide by 1000)

5

## What are the three steps to moles mass and mr equation

###
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

6

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

###
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

7

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

### Moles = concentration x volume

8

## What is concentration equation

### Conc = moles/vol

9

## Important conversions for concentration equation

###
Cm 3 to dm3 = divide by 1000

Dm 3 to m 3 = divide by 1000

Cm 3 to m3 = divide by 1000000

10

## Steps to calculating normal concentration equation

###
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

11

## Steps to find concentration when given the mass of a reactant

###
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

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

###
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

13

##
ZnO + 2HCl -> ZnCl2 + H20

ZnO = 0.0830 moles

2HCl = 100cm3 and 1.20 mol dm-3

Find the mass of ZnCl2

###
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

14

## What is the molecular formula ?

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

15

## What is a standard (volumetric ) solution ?

### A solution that you know the exact concentration of

16

## What does the making of a standard solution involve ?

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

17

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

###
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

3. Subtract mass of boat from mass of boat and solid together = find precise mass of solid. (Record difference).

4. Add distilled water to beaker (eg 100dm3) and stir until sodium hydroxide dissolved

5. Pour solution into 250 cm3 volumetric flask using funnel

6. Rinse beaker , stirring rod with distilled water and add washing to flask

7. Add solvent to correct volume until graduation line then drop by drop until bottom of meniscus reaches the line.

8. Invert flask several times to make sure it is mixed and a uniform solution

18

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

### Makes sure no solute clings to the beaker or rod

19

## What do titrations allow you to do ?

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

20

## What is the method for titration

###
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

3. Fill Burette with standard solution of acid HCl) mention what concentration the HCL or acid is

4. Use funnel to pour acid into burette - done at eye level

5. Do rough titration to get idea of end point by adding acid to alkali using burette and give flasks regular swirls

6. Do accurate titaration

Take initial reading of acid

Run acid with 2cm3 of end point

Add acid drop wise until end point reached

21

## How do you find volume of titre

### Final reading - initial reading

22

## Until when should you repeat the titration

### Until you have 3 concordat results

23

## What is a anomalous result

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

24

## What kind of indicators should be used ?

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

25

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

###
So that all the solution reacts with each other and is in the flask

Water does not change number of moles in either reactant

26

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

### Droplet from funnel could enter the burette and effect the readings

27

## What is the source of error in using a burette

### Air bubbles

28

## What is the effect of the air bubble

### The value of the titre would be higher

29

## Why is a conical flask used rather than beaker

### Less chance of losing liquid in swirling

30

## How do you calculate % uncertainty

### Error/ measurement x 100

31

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

###
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)

32

## How can you reduce uncertainty ?

###
Reducing the error (eg more accurate balance or apparatus with greater resolution)

Decrease concentration of solution in burette to increase volume measurement

33

## What do burettes measure and let you do ?

### Measure different volumes and lets you add solution drop by drop

34

## What do pipettes measure

### Only one volume of solution

35

## If there is only two results what should you do ?

### Do further titrations for concordant results

36

## How is the method for standard solution accurate

###
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

37

## What is the ideal gas equation

### PV=nRT

38

## What are all the units of the ideal gas equation

###
P= pressure (Pa)

V= volume (m3)

N= number of moles

T= temperature (k)

39

##
Volume:

Dm3 to m3

Cm3 to m3

###
Dm3 to m3 = divide by 1000

Cm3 to m3 = divide by 1000000

40

##
Pressure :

Kpa to pa

Map to pa

Atmosphere

###
Kpa- pa X 1000

Mpa- pa X100000

Atmosphere - x101325

41

## How do you convert Celsius to K

### C + 273

42

## What is the rule for volume of gases

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

43

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

### Mr/ Avogadro constant

44

## Ideal gas equation rearranged

###
For number of moles = Pv/rt

Temperature = pv/ nr

Volume = nRt/p

Pressure = nRt/V

45

## What is the formula for atom economy

### Mass of wanted product from equation / total mass

46

## What is the formula for percentage yield

### Mass of product formed / maximum theoretical mass of product

47

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

###
Better for environment so they produce less waste

More efficient use of raw materials so more sustainable

Less expensive

48

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

###
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 %

49

## Why do we re weigh the boat ?

### It may contain traces of solid

50

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

###
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

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

###
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

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

###
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

53

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

###
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

54

## How do you find the empirical formula

###
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

55

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

###
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

56

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

###
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

57

## How do you convert from mol dm3 to g dm3

### Multipliy by mr

58

## How can you check if all the water has been removed

### Reheat until mass hasn’t changed

59

## Empirical formula question

###
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

60