C4-Quantitve Chemistry Flashcards
(122 cards)
1
Q
What is the conservation of mass
A
The law of conservation of mass states that no atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants.
2
Q
What is the limiting reactant
A
The reactant that is completely used up since it limits the amount of products formed.Whilst the other reactant is in excess
3
Q
What is a mole
A
The mole is the unit for amount of substance. The symbol for the unit mole is mol.
4
Q
What is a relative formula mass
A
The sum of the relative atomic masses of the atoms in the numbers shown in the formula.
5
Q
What is the percentage yield
A
The percentage ratio of the actual yield of product from a reaction compared with the theoretical yield.
6
Q
What is concentration
A
The amount of substance in a certain volume of solution
7
Q
What is the actual yoeld
A
Amount of product actually produced by a feaction
8
Q
What is atom economy
A
The measure of the amount of starting materials that end up as useful products
9
Q
What is the theoretical yield
A
The maximum amount of product that could be produced from the given reactants assuming a complete reaction takes place
10
Q
How to get the relative formula mass
A
Its mass number added to another
11
Q
How to calculate the % mass of an element in a compound
A
Relative atomic mass x number of atoms of that element/relative formula mass times 100
12
Q
Example to find the % mass of an element in a compound. Na2CO3.Finding sodium in it
A
Ar of sodium=23 Ar of carbon=12. Ar of oxygen=16
Relative formula mass=(2x23)+12+(3x16)=106
23x2/106 x100=43%
13
Q
A mixture contains 20% iron irons by mass.What mass of iron chloride (Fecl2) would you need to provide the iron ions in 50g of the mixture? Example
A
Ar of Fe=56 Ar of cl=35.5
Mixutre of ion contains=10g of iron
56/56(2x35.5) x100=44.09%
10/44.09/100=23 g
14
Q
What is percentage composition also know as?
A
Percentage mass
15
Q
How to calculate relative atomic mass
A
Its a numbers mass number
16
Q
How to calculate the number of moles
A
Mass in g (of an element or compound) / Ar or Mr(of the element or compound)
17
Q
What is avogardos constant
A
the number of atoms, molecules, or ions in a mole of any substance (i.e., 6.02 × 10-23 per mol)
18
Q
What is titration
A
a method for measuring the volumes of two solutions that react together
19
Q
What is the end point
A
the point in a titration where the reaction is complete and titration should stop
20
Q
What is burette
A
a long glass tube with a tap at one end and markings to show volumes of liquid; used to add precisely known volumes of liquids to a solution in a conical flask below it
21
Q
What is the concordant
A
when you have two titration results that are within 0.1cm3 of each other. These precise results can then be used to
calculate an accurate mean
22
Q
What is a bulb pipette
A
a glass tube used to measure accurate volumes of liquids
23
Q
What is uncertainty
A
Range of measurements each side of the mean
24
Q
How to calculate uncertainty
A
Calculate mean and then calculate range and the difference is the uncertainty.Make sure before you always add a +/-
25
What is the mass of 1 mole equal to
The mass of 1 mole of a substance is equal to its relative formula mass or atomic mass in grams
26
What does a balanced equation show
Shows reacting moles of each substance(as the simplest whole number ratio)
27
How to calculate the maxiumum mass of a substance
Step 1. note what you know and what to calculate - you can ignore the other substances
Ignore the big numbers for the moment - we will use them later
Step 2. Calculate the moles of the substance that you know the mass of
Step 3. Use the ratio of moles from the balanced equation to work out the number of moles of the substance with unknown mass ratio of moles is 2: 2
So there will be 0.675 moles of MgO as well
Rearrange and calculate the answer
28
We can only work out the limting reactant if we know
-Number of moles that react in a experiment
-Balanced formula equation
29
How to measure concentration
Measured in g/dm^3 or mol/dm^3
30
What does 1dm3 equals
1000 cm3
31
How to calculate concentration
Mass/volume
This is also converting from dm^3 to g/dm^3
32
How to calculate mass
Concentration x volume
33
Calculation to calculate moles in solutions
Concentration x volume
34
In a chemical reaction why do we not always obtain the mass of the product calculated
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.
Note-This is about yield and practical losses.
35
What is the yield
The amount of product obtained in a chemical reaction
36
How to calculate percentage yield
Mass of product actually made/max theoretical mass of product x100
37
Example question-Zinc reacts with copper sulfate to produce 30g of copper.The theoretical yield of copper is 35g.Calculate the percentage yield
Percentage yield=30/35 x100
85.7%
38
Why is high atom economy important
Contributes to sustainable development
Saves costs
39
How to calculate atom economy
Relative formula mass of desired product/Sum of the relative formula mass of all reactants in the equation X100
40
How to calculate volumes of gasses
Mass of gas/relative formula mass x 24=volume dm^3
41
Value for avogadros constant
6.02 x 10^23
42
If the amount of solute in a solution is increased what happens to its concentration
Increases
43
If the volume of water in a solution is increased what happens to its concentration
Decreases
44
How should solution be added from the burette close to the end point
Drop by drop,swirling in between
45
Why is a white tile used in titratiom
See colour change better
46
What is a titre
Volume of solution added from thr burette
47
What volume does one mole of any gas occupy at room temperature and pressure?
24dm^3 or 24000 cm3
48
How do we know usually if there is a gas
If the mass seems to change
49
Explanation of when the mass increases
If the mass increases its probably because one of the reactants is a gas that is found in air and all the products are solid liquids or aqueous.
50
when a mass increases what happens
Before the reaction the gas is floating around in the air.Its there but its not contained in the reaction vessel,so you cant account for its mass
When the gas reacts to form part of the product it becomes contained inside the reaction vessel so the total mass of the stuff increases
51
Explanation of when the mass decreases
Due to one of the products being a gas and the reactants being solid liquids or aqueous
52
When a mass decreases what happend
Before the reaction all the reactants are contained in the reaction vessel.
After if the vessel isnt enclosed then the gas can escape from the reaction vessel as irs formed.Its no longer contained in the reaction vessel so you cant account for its mass.The total mass of the stuff inside decreases
53
How to calculate relative atomic masses
(Isotope 1 times abundance) +(isotope 2 times abundance) divided by 100
54
What is the relative formula mass equal to
It is numerically equal to the mass of one mole of a substance in grams.
55
How to calculate mass of a given number of moles
Mass=moles x relative formula mass
56
What is a standard solution
A standard solution is one of known concentration
57
How to increase the concentration of a aqueous solution
adding more solute and dissolving it in the same volume of its solution
evaporating off some of the water from the solution so you have the same mass of solute in a smaller volume of solution.
58
Name two acid/base indicators that can be used in the titration between dilute hydrochloric acid and sodium hydroxide solution.
Methyl orange,phenoplthaien
59
What colour does phenolphthalein turn in acid/after tiration and base
Colourles in acid
Pink in base
60
What colour is methyl orange in acid/titration and base
Orange in base
Pink in acid
61
What are the soluble salts
Sodium
Lithium
Ammonium
Potassium
Nitrate
62
What is the molar ratio
The molar ratio is the ratio between the moles of different reactants and products in a balanced equation.
63
Example of molar ratio
N2+3H2 = 2NH3
Ratio of n2:H2:NH3 is 1:3:2
64
What is the relationship between dm^3 and litres
1dm^3=1 litre
65
How to calculate dm^3
Vol in cm^3/1000
66
How to calculate concentration g/dm^3
Concentration mol/dm^3 x Mr
67
How to calculate volume
Mass/concentration
68
Define nuetralisation
Neutralisation is when an acid reacts with a base, to form a neutral solution. A base that can dissolve in water is called an alkali.
69
How to calculate the number of moles in a gas in dm^3
Volume/24
70
How to calculate the number of moles of a gas in cm^3
Volume/24,000
71
What is empirical formula
Ratio of atoms
72
How to calculate empircal formula
Moles = Mass ÷ Atomic Mass (Ar)
🔹 Simplest Ratio = Divide by the smallest value
🔹 Write the empirical formula using the ratio
73
What is combustioN
Burning in air
74
Example of emperical formula question
Given percentages:
Carbon (C): 72%
Hydrogen (H): 12%
Oxygen (O): 16%
Step 1: Divide by Atomic Mass (Ar)
Carbon: 72 ÷ 12 = 6
Hydrogen: 12 ÷ 1 = 12
Oxygen: 16 ÷ 16 = 1
Step 2: Divide by the Smallest Number
Carbon: 6 ÷ 1 = 6
Hydrogen: 12 ÷ 1 = 12
Oxygen: 1 ÷ 1 = 1
Step 3: Write the Empirical Formula
C₆H₁₂O
75
Unit for volume
Cm^3 or dm^3
76
What is the element in excess
The element which has not been fully used up.still has left
77
How can chemical reaction be represented
78
What does a number in front of a formula (normal script) represent in an equation?
It is a multiplier that tells you how many molecules or units of the substance are involved.
📌 Example: In 2H₂O, the "2" means 2 molecules of water.
79
What does a small number in a formula (subscript) mean?
It tells you how many atoms of an element are in one molecule.
📌 Example: In H₂O, the "2" means 2 hydrogen atoms in 1 molecule of water.
80
In the formula 3CO₂, how many atoms of each element are there in total?
There are 3 carbon atoms and 6 oxygen atoms.
(3 × 1 C and 3 × 2 O)
81
In a balcned chemical equation what does the sum of relative formula masses of the reactants show?
In a balanced chemical equation, the sum of the relative formula
masses of the reactants in the quantities shown equals the sum of
the relative formula masses of the products in the quantities shown.
82
What happens to mass when a metal reacts with oxygen?
The mass increases because oxygen from the air is added to the metal, forming a metal oxide.
83
What happens to mass during the thermal decomposition of a metal carbonate?
Observation: The mass of the solid product (calcium oxide) is less than the mass of the original calcium carbonate.
Explanation: Carbon dioxide gas is produced and escapes into the atmosphere, reducing the measurable mass.
Particle Model: Particles of carbon dioxide leave the system, so fewer particles remain, resulting in a lower measurable mass.
84
How do you explain mass changes using a balanced equation and the particle model
Use the balanced equation to show what atoms are present before and after the reaction.
Then use the particle model to explain if any gas particles enter or escape. If they do, and the container is open, the measured mass will change even though no atoms were destroyed or created.
85
Example: If your results are 24.0, 24.5, 23.5, 25.0, 23.0, what is the mean and uncertainty?
Mean = 24.0
Range = 25.0 - 23.0 = 2.0
Uncertainty = ±1.0
Final answer: 24.0 ± 1.0
86
What is a random error?
Random errors cause results to vary in an unpredictable way, due to things like reading instruments differently each time
87
What is a systematic error?
Systematic errors consistently shift results in one direction, often due to faulty equipment or technique
88
What does one mole of a substance contain?
One mole of a substance contains the same number of the stated particles, atoms, molecules or ions as one mole of any other
substance.All contain 6.02 x10^23 particles
89
What types of particles can the mole be used to count, and what does one mole of different substances contain?
A mole can count atoms, molecules, ions, electrons, formula units, and equations.
90
What is the effect of a limiting reactant on the amount of product formed in a reaction?
The limiting reactant is completely used up first and stops the reaction. It limits the amount of product formed because the product amount depends on the moles (or mass) of the limiting reactant. Other reactants remain in excess and don’t affect the product amount.
91
What does mass per volume mean?
g/dm^3
92
What does concentration depend on?
Concentration depends directly on mass and inversely on volume.
93
What does this mean if concentration depends on mass and volume ?
If you increase the mass of solute but keep volume the same, concentration increases.
If you increase the volume of solution but keep mass the same, concentration decreases.
94
How do you explain changes in mass in non-enclosed systems during a chemical reaction, using the particle model?
In a non-enclosed system, gases can enter or leave during a chemical reaction.
If a gas is produced and escapes, the total mass decreases (e.g. metal + acid → hydrogen gas escapes).
If a gas from the air is used, the total mass increases (e.g. magnesium reacts with oxygen from air).
The particle model explains this as particles of gas either escaping into or entering from the surroundings, changing the total measurable mass.
95
Even if no atoms are gained or lost in a chemical reaction can the calculated amount of product change?
Even though no atoms are gained or lost in a chemical reaction, it is not always possible to obtain the calculated amount of a product
96
How do you calculate the theoretical mass of a product from a given mass of reactant and a balanced equation?
Write the balanced symbol equation.
Calculate the Mr (relative formula mass) of the reactant and the product.
Calc the moles by mass/mr
Use the mole ratio from the balanced equation to find the moles of product formed.
Calculate the mass of the product using:
Mass=moles x mr
97
Another way of saying atom economy
atom utilisation
98
Why is a particular reaction pathway chosen to produce a product? What factors are considered?
A reaction pathway is chosen based on data like:
Atom economy – higher atom economy = less waste = more sustainable
Percentage yield – higher yield = more product made
Rate of reaction – faster reactions are more efficient for industrial use
Equilibrium position (for reversible reactions) – more product is made if equilibrium lies to the right(the product)
Usefulness of by-products – useful by-products can increase profit and reduce waste; harmful ones may need expensive disposal
99
What is the equilibrium position?
Equilibrium position is a term used to describe where the balance lies between reactants and products in a reversible chemical reaction when it reaches equilibrium.
100
What does the equilibrium position mean?
In a reversible reaction, the reaction can go forwards (reactants → products) and backwards (products → reactants).
After a while, the reaction reaches a point where the rate of the forward reaction equals the rate of the backward reaction. This is called dynamic equilibrium.
At equilibrium, the amounts of reactants and products remain constant (but not necessarily equal).
The equilibrium position tells us which side (reactants or products) is favored — meaning, which side has the greater amount of substances at equilibrium.
101
What is use-fullness of products?
Usefulness of products” means how valuable or practical the products of a chemical reaction are.
102
What is a by-product?
A by-product is a substance that is produced alongside the main product during a chemical reaction but is not the main thing you want.
103
Why is usefulness of products important
It affects the economic value of the reaction — more useful products mean better profits.
It impacts environmental concerns — useful or recyclable by-products reduce waste.
104
How do you convert g/dm^3 to mol/dm3
G/dm^3/g/Mr
105
Explain how the concentration of a solution in mol/dm³ is related to the mass of the solute and the volume of the solution.
So, concentration increases if mass of solute increases (at constant volume).
Concentration decreases if volume increases (at constant mass).
106
The volume of one mole of any gas at room temperature and pressure (20°C and 1 atmosphere pressure) is
24 dm3
.
107
What is the empirical formula
The empirical formula is the simplest whole-number ratio of atoms of each element in a compound.
108
How to calculate the empirical formula?
It is calculated by:
Determining the mass (or percentage) of each element in the compound.
Dividing the mass of each element by its relative atomic mass (Ar) to find the number of moles.
Dividing all the mole values by the smallest mole value to find the simplest ratio.
If necessary, multiplying the ratios to convert them into whole numbers.
109
How do you identify the limiting reactant and calculate the amount of product formed?
Write the balanced chemical equation.
Calculate the moles of each reactant using: moles = mass / Mr.
Use the molar ratio from the balanced equation to determine which reactant produces the least amount of product (this is the limiting reactant).
Use the moles of the limiting reactant and the molar ratio to calculate the moles of product.
Calculate the mass of the product: mass = moles × Mr.
110
Example of calculating the limiting reactant
For the reaction 2H₂ + O₂ → 2H₂O, if 4g of H₂ and 40g of O₂ are used:
Moles of H₂ = 4 / 2 = 2 mol.
Moles of O₂ = 40 / 32 = 1.25 mol.
Molar ratio (H₂:O₂) is 2:1, so 2 mol of H₂ needs 1 mol of O₂. O₂ is in excess (1.25 > 1), so H₂ is limiting.
Moles of H₂O = 2 (same as H₂ due to 2:2 ratio).
Mass of H₂O = 2 × 18 = 36g.
111
What is percentage error
Percentage error measures the accuracy of an experimental measurement compared to the true value.
112
How to calc percentage error
Formula: Percentage error = (|Experimental value − True value| / True value) × 100.
113
Example of percentage error
A burette measures 25.0 cm³, but the true volume is 24.8 cm³.
Difference = |25.0 − 24.8| = 0.2 cm³.
Percentage error = (0.2 / 24.8) × 100 = 0.81%.
114
How does the molar volume of a gas change with temperature and pressure?
The molar volume of a gas (volume occupied by 1 mole) is 24 dm³ at room temperature (20°C) and 1 atm pressure.
If temperature increases, molar volume increases (gas particles move further apart).
If pressure increases, molar volume decreases (gas particles are compressed).
115
How to calculate uncertainity
Calculate the mean
Calculate the range
Then divide the range by 2 and that is your uncertainity to the mean
116
What is excess
More of a chemical than you need for a
reaction.
117
Can you lose mass in an enclosed system
In a perfectly sealed, isolated system, no particles are lost or gained, so the mass remains constant. Any apparent changes in mass are due to experimental or practical factors.
118
What can happen in an non-enclosed system?
In a non-enclosed system, particles (like gases) can escape or enter.
Note-This is about mass changes observed during the reaction because gases can enter or leave the system.
119
What is the particle model?
The particle model is a simple way scientists explain how matter behaves by imagining that everything is made up of tiny particles (atoms, molecules, or ions). It helps us understand the properties of solids, liquids, and gases, and how they change during physical and chemical changes.
120
What is the difference between concentration in g/dm³ and mol/dm³?
g/dm³ (grams per dm³): Measures the mass of solute (in grams) dissolved in 1 dm³ of solution.
mol/dm³ (moles per dm³): Measures the amount of solute (in moles) dissolved in 1 dm³ of solution.
121
How to calculate concentration in solution
Moles/volume
mol/dm^3
122
In gases what do equal amounts in moles occupy?
Equal amounts in moles of gases occupy the same volume under
the same conditions of temperature and pressure.
