Separate Chemistry - 5.3 Flashcards

1
Q

What does the law of the conservation of mass state?

A

No atoms are lost or made during a chemical reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

A piece of magnesium is added to acid. What would happen to the mass reading on the balance and why?

A

It would stay the same because there is a lid on the conical flask so no gas can escape.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Count the number of elements in the following compounds:

a) CaO
b) Al2O3
c) H2SO4

A

a) CaO - 2 elements (Ca and O)
b) Al2O3 - 2 elements (Al and O)
c) H2SO4 - 3 elements (H, S and O)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Count the number of atoms in the following compounds:

a) CaO
b) Al2O3
c) H2SO4

A

a) CaO - 2 atoms (1 x Ca and 1 x O)
b) Al2O3 - 5 atoms (2 x Al and 3 x O)
c) H2SO4 - 7 atoms (2 x H, 1 x S and 4 x O)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Calculate the relative formula mass (Mr) of each of the compounds (a, b & c) below.

AR: Mg = 24; Cl = 35.5; Ca = 40; O = 16; Al = 27

a) CaO
b) MgCl2
c) Al2O3

*this is just an example, you need to be able to do this for any compound.

A

a) CaO: 40 + 16 = 56
b) MgCl2: 24 + (35.5x2) = 95
c) Al2O3: (27x 2) + (16 x 3) = 102

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

A piece of magnesium is added to acid. What would happen to the mass reading on the balance and why?

A

It would decrease because there is no lid on the conical flask so gas can escape and therefore mass is ’lost’ from the flask.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Calculate the uncertainty in the following sets of results

a) 1, 3, 6, 7, 10
b) 22, 25, 26, 25, 24

*this is just an example, you need to be able to do this for any set of data given.

A

Use the equation: uncertainty = range / 2

a) 1, 3, 6, 7, 10

Range = 10 – 1 = 9. Uncertainty = 9/2

Uncertainty = ± 4.5

b) 22, 25, 26, 25, 24

Range = 26 – 22 = 4. Uncertainty = 4/2

Uncertainty = ± 2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Calculate the percentage mass of hydrogen in:

Ar: N = 14 ; H = 1 ; S = 32 ; O = 16.

a) NH3
b) H2SO4

Give your answer to the nearest whole number.

*this is just an example, you need to be able to do this for any compound when given the appropriate information.

A

% mass = (Ar x number of atoms of the element) / (Mr of compound) x 100

a) NH3 : (3x1) / 17 = 0.176
0. 176 x 100 = 18 %
b) H2SO4 : (2x1) / 98
0. 02 x 100 = 2 %

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Separate Q. Give three reasons why you might not achieve the amount of product you have calculated (theoretical yield).

A
  • The reaction may not go to completion because it is reversible.
  • Some of the product may be lost when it is separated from the reaction mixture.
  • Some of the reactants may react in ways different to the expected reaction.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Separate Q. What does ‘yield’ mean?

A

The amount of product that is obtained

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Separate Q. What equation would you use to work out the percentage yield of a reaction?

A

% yield=(actual yield)/(theoretical yield) x 100

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Separate Q. What does atom economy mean and why is it important?

A
  • Atom economy is a measure of the amount of starting materials that end up as useful products.
  • It’s important for sustainable development and economical reasons.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Separate Q. How would you calculate percentage atom economy?

A

% atom economy = (Mr of desired product) / (Sum Mr of all reactants) x 100

How well did you know this?
1
Not at all
2
3
4
5
Perfectly