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C4 Chemical Calculations Flashcards

(51 cards)

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1
Q

Why some elements have same relative mass as each other

A

Although the number of protons in the nucleus is the same for all atoms of the same element, the number of neutrons is not

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2
Q

Why some relative atomic masses may not be a whole number

A

Due to existence of isotopes having different mass numbers

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3
Q

Unit for amount of substance

A

Mole
23
1 mole = 6.02 x 10

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4
Q

Why chemical equations must be balanced

A

So it follows the law of conservation of mass

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5
Q

The effect of a limiting reactant on the amount of product made

A

Limits how much product can be formed

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6
Q

Limiting reactant

A

The reactant that gets consumed first in a chemical reaction

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7
Q

Theoretical yield

A

The maximum possible mass of a product that can be made in a chemical reaction

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8
Q

Actual yield

A

The actual mass of a product made in a chemical reaction

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9
Q

Percentage yield

A

(Actual yield ➗ theoretical yield) x 100

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10
Q

Why actual yield is often lower than theoretical yield

A

Some of the reactants do not react to form the product

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11
Q

Why percentage yield can never be over 100%

A

Incomplete reactions, some of reactants don’t react to form the product

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12
Q

How to calculate formula mass

A

Add masses of all atoms

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13
Q

Atom economy

A

A measure of efficiency of a chemical reaction

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14
Q

How to calculate atom economy

A

total number of atoms in the desired product
_________________________________________________________

 total number of atoms in all the reactants
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15
Q

Why using reactions with high atom economy is important

A

Uses fewer natural resources

Produce less waste

Better for environment

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16
Q

Why the sum of the formula masses of the reactants is the same as the sum of the formula masses of the product

A

All atoms making up the reactants are still in the products

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17
Q

How concentration of solution can be changed

A

Increasing amount of solute

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18
Q

2 ways to calculate concentration of solution

A

Mass of solute ➗ volume of solvent

Number of moles of solute ➗ volume of solvent

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19
Q

How to calculate a titre

A

Values added together divide number of readings that were taken

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20
Q

Use of pipette for titration

A

To accurately measure a fixed volume of liquid

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21
Q

How an indicator can be used to determine the end point

Study These Flashcards
A

Helps us spot the equivalence point in an acid-base titration

22
Q

How precise results are obtained in a titration

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A

Relies on accurate volume measurement

23
Q

How accuracy can be improved in a titration

Study These Flashcards
A

Calibrate your electrode regularly

24
Q

Use of an indicator in an acid-base titration

Study These Flashcards
A

To signal the end of a titration

25
How the volume of gas would change when temperature was changed
Volume increases as temperature increases Molecules of gas have more kinetic energy
26
Percentage of mass of an element in a compound Find percentage mass of sodium in sodium carbonate Na2CO3
Na = 23 Na2CO3 = 106 23 x 2 ________ x 100 = 43% 106
27
Surface area to volume ratio =
Surface area ➗ volume
28
What happens to mass in a chemical reaction
Mass is always conserved
29
Why are there always the same number of atoms on each side of reaction equation
No atoms are destroyed or created
30
If mass reaction may seem to change what could be a cause to this
Because one of the reactants is a gas found in air and all the products are solids, liquids or aqueous
31
Why does mass increase if one of reactants are a gas
Before reaction, gas is floating in the air but not contained in reaction vessel so can't account for its mass When gas reacts to form part of the products, it becomes contained inside reaction vessel so total mass inside reaction vessel increases
32
Why might mass decrease in a chemical reaction
Before reaction all rectants are contained in reaction vessel If vessel isn't enclosed gas can escape from reaction vessel as it's formed It's no longer contained in reaction vessel so you can't account for its mass Total mass of stuff inside reaction vessel decreases
33
Why might mass seem to decrease in chemical reaction
One of products is a gas and all the reactants are solids, liquids or aqueous
34
When does a chemical reaction stop
When one of reactants is used up Any others are in excess
35
What is amount of product formed directly proportional to
Amount of limiting reactant
36
How much volume does 1 mole of any gas occupy at 20°C
24dm3 20°C = atm = at room temperature
37
Volume of gas =
Mass of gas ______________ x 24 Mr of gas
38
Mr =
Relative formula mass
39
r.t.p
Room temperature and pressure
40
What's the volume of 319.5 g of chlorine at r.t.p?
319.5 ________ x 24 = 108dm3 71 (Cl2)
41
In the question What's the volume of 319.5 g of chlorine at r.t.p? Why is it mass of Cl2 instead of Cl
Because chlorine naturally exists as a diatomic molecule in its gaseous form So need 2 chlorine atoms
42
Elements that naturally exist as diatomic molecules in their gaseous form
Bromine Iodine Nitrogen Chlorine Hydrogen Oxygen Fluorine
43
What's the concentration in g/dm of a solution of sodium chloride where 30 g of sodium chloride is dissolved in O.2 dm of water?
30 ➗ 0.2 = 150g/dm3
44
What's the concentration, in mol/am?, of a solution with 2 moles of salt in 500 cm?
Convert cm3 to dm3 by ➗1000 500 ➗ 1000 = 0.5dm3 2 ➗ 0.5 = 4mol/dm3
45
Titration
Experiments that let you find the volumes needed for 2 solutions to react together completely
46
What does 0% percentage yield mean
No reactants were converted into product so no products was made
47
What does 100% percentage yield mean
You got all ghe product you expected to get
48
What are 3 common reasons some produtpct or reactant gets lost along the way
Not all reactants react to make a product There might be side reactions You lose some product when you separate it from the reaction mixture
49
Why can yield never be 100% in reversible reactions
The products can turn back into reactants
50
How could there be side reactions
Reactants could react with gases in the air or impurities in reaction mixture so end up forming extra products other than the one syou want
51
Mole
23 Mass of a substance that contains 6.02 x 10 particles

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