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Chemistry > Chemical Quantities and Calculations > Flashcards

Chemical Quantities and Calculations Flashcards

1
Q

What is a chemical reaction?

A

It is a process that leads to the transformation of one set of chemical substances to another. It is an irreversable or reversible change where chemical bonds are made or broken to form new compounds.

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2
Q

Here is a question to do with the conservation of mass:
If I had 20g of calcium carbonate and react this with 25g of sulphuric acid, I make 32g of calcium sulphate, 3g of water and how many grams of carbon dioxide?

A

CaCO3+H2SO4—->CaSO4+H2O+CO2
20g +25g —->32g +3g + ?
45g —-> 35g+ x
45-35=10 x=10
10g of CO2

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3
Q

Tips

A

Always check units are constant

If the question gives a number as two dp then give the answer as two dp unless said otherwise.

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4
Q

What is the law of the conservation of mass?

A

Mass is neither created or destroyed in chemical reactions. In other words, the mass of any one element at the beginning of a reaction will equal the mass of that element at the end of the reaction.

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5
Q

If I have 12.8g of copper and react it with oxygen to produce 16g of copper oxide, how much oxygen did the copper rect with? Make sure the equation is balanced.

A 
copper+oxygen----> copper oxide
 Cu     + O2       ---->  CuO
 2Cu   + O2       ---->  2CuO
12.8g  +  ?         ----> 16g
16-12.8=3.2   
3.2g of O2
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6
Q

Any element with OH is an alkali/acid?

A

alkali

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7
Q

Balance this equation…

Al+O2—->Al2O3

A

4Al + 3O2 —-> 2Al2O3

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8
Q

Name the equipment required for the oxidation of magnesium.

A
  • Heatproof mat
  • Tripod
  • Heat source like a bunsen burner
  • Pipeclay Triangle
  • Crucible and lid
  • Tongs
  • Mass balance (scales)
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9
Q

Name the equation for the oxidation of magnesium.

A

Magnesium+Oxygen—>Magnesium Oxide

2Mg + O2 —-> 2MgO

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10
Q

Why is relative formula mass called this?

A

We call it relative because you can only compare it.

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11
Q

Can you weigh an atom?

A

You cannot weigh an atom as its mass is too small, you can only make a guess.

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12
Q

What is used to in theory ‘weigh’ an atom?

A

A mass spectrometer is used to in ‘theory’ weigh an atom.

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13
Q

What element are all other elements relative masses compared to? How much heavier is this element than Helium?

A

Carbon 12

It is 3x heavier than Helium

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14
Q

What are atoms ‘measured’ in?

A

Moles(mol)

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15
Q

What is the relative formula mass of water?

A 
H2O
2x1=2
1x16=16  
16+2=18
water's relative formula mass= 18
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16
Q

What is the relative formula mass of NH4NO3?

A

N=14 2x14=28
H=1 4x1=4
O=16 3x16=48

28+4+48=80
The relative formula mass is 80

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17
Q

What is the relative formula mass of Ca(NO3)2?

A 
Ca=40    1x40=40
N=14       2x14=28
O=16      6x16=96
40+28+96=164
The relative formula mass is 164
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18
Q

What is the total number of atoms shown in the formula K2SO4?

A

7 atoms

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19
Q

If you change the proton number of an element what happens?

A

If you change the proton number then you change the element.

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20
Q

If chlorine had one more proton what element would it become?

A

It would become argon.

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21
Q

What do the electrons effect?

A

They effect the charge of the element not what the element is itself.

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22
Q

If an atom gains one more electron what charge does it have and what is the atom called?

A

It has a negative charge.

It is known as a anion.

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23
Q

If an atom loses one electron what charge does it have and what is the atom called?

A

It has a positive charge.

It is known as a cation.

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24
Q

What is an isotope?

A

It’s the variation of an atom.

25
Q

What is the purpose of neutrons?

A

Neutrons add mass and keep the element stable.

26
Q

Why is chlorine’s atomic mass 35.5?

A

It’s the average of all of it’s isotopes. You can’t have 0.5 of a proton/neutron.

27
Q

What are the units for moles?

A

mol

28
Q

How do you work out the mass of an element used?

A

mass= MolesxRAM

29
Q

How do you work out the Moles in an element used?

A

moles= mass/RAM

30
Q

What does RAM stand for?

A

RAM= Relative atomic mass

31
Q

How do you work out the RAM of an element used?

A

RAM= mass/moles

32
Q

What is Avogadro’s Number?

A

It is the number of atoms in a mole…

6.022x10tothepowerof23

33
Q

Why do we use the mole? Hint:It is just a conversation factor.

A

A mole is just a conversation factor used to help us as accurately as possible to work with atoms and molecules.

34
Q

How many moles are in 48g of magnesium?

A

Mg
48/24=2
2mol

35
Q

How many moles are in 9.8g of sulphuric acid?

A

H2SO4
2+32+64=98
9.8/98=0.1
0.1 mol

36
Q

How many moles are in 1kg hydrogen atoms?

A

1000/1=1000

1000mol

37
Q

How many moles are in 1kg of hydrogen molecules?

A

H-H
1000/2=500
500mol

38
Q

What is the mass in grams of 10mol lead?

A

10x 207=2070

2070g

39
Q

How many particles are there in 0.5 mol of water?

A

mole= 6.02x10tothepowerof23

0.5mol=3.01x10tothepowerof23

40
Q

Does one mol of copper weigh the same as one mol of water or two mol of hydrogen?

A

It weighs the same as one mol of any substance.

41
Q

Use the Ar value to calculate the molar mass(Mr) of sodium.

A

Na=23

23g/mol

42
Q

What is copper sulphate(aq) short for? Is it a mixture this substance?

A

Copper sulphate crystals disolved in water.

It is a mixture.

43
Q

What does diatomic mean?

A

These are elements that go round in twos. Eg H2 or O2

44
Q

What is the product of H2+O2—->?

Don’t forget to balance the equation out.

A

H2+O2—->H2O
This is because covalent bonding is used to make the elements whole. Oxygen needs two more electrons to become whole so you use two hydrogens. In order for the hygiene to become whole they need to gain one more electron each so share with oxygen.
2H+O2—->2H2O === balanced

    x             xx        :                  xx
  H H   +  xx O xx: O : ----> H x.Ox.H
    x                                            xx
45
Q

Give examples of valency.

A

Group 1 needs electron(s) from group 7 to be complete.
2 6
3 4

46
Q

What bonding is relevant to valency?

A

Ionic Bonding

47
Q

Show the bonding between sodium and bromine.

A 
Sodium+Bromine----> Sodium Bromide
ionic bonding
 x           :
Na      . Br :
              :
\_\_         \_\_+        \_\_   \_\_-
|     xx        |         |    :      |
| xx Na xx |         |  : Br :  |
|      xx       |         |    :      |
|\_\_        \_\_|         |\_\_  \_\_|
Cation                 Anions
2Na + Br2----> 2NaBr
48
Q

4g of hydrogen reacts with 32g of oxygen. How much oxygen reacts with 40g of hydrogen?

A

320g

49
Q

Simplify these ratios= 11:33

39:65

A

1: 3
3: 5

50
Q

Give an example of a molecular/chemical formula.

A

H2O

51
Q

Give an example of a structural formula.

A

CH3CH2CH2OH

52
Q

Give an example of a displayed formula.

A 
H H H
     |   |   |
H-C-C-C-O-H
     |   |   |
    H H H
53
Q

What is an empirical formula?

A

The simplest ratio in a compound.
Eg: C2H6
simplifies to CH3

54
Q

Find the empirical formula of the iron oxide produced when 44.8g of iron reacts with 19.2g of oxygen.

A 
Fe                                     O
56=RAM                           16=RAM
44.8/56=0.8mol               19.2/16=1.2mol
           10x0.8=8                      10x1.2=12
                              8:12
                              2:3
Answer=Fe2O3
Can be done with more than two numbers.
55
Q

How is the ionic compound of ammonium sulphide written?

A

Sulphur= S 2-
Ammonium=NH4 +
(NH4)2 S

56
Q

Complete the table…
Empirical Formula | Mr | Molecular Formula
CH2 | 42 | a
b | c | C4H8
C3H8 | 44 | d

A

a=C3H6
b=CH2
c=56
d=C3H8

57
Q

Why when preforming the oxidation of magnesium is the amount of magnesium oxide produced not as efficient as it could be?

A
  • Air isn’t just oxygen
  • Not heated to a high enough temp to have a complete reaction
  • There is only a limited amount of oxygen in the crucible
58
Q

Why does magnesium gain weight when becoming magnesium oxide?

A

The oxygen bonds with the magnesium.

Chemistry (4 decks)

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