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Chemistry > C4 Chemical Calculations > Flashcards

C4 Chemical Calculations Flashcards

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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

A

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

22
Q

How precise results are obtained in a titration

A

Relies on accurate volume measurement

23
Q

How accuracy can be improved in a titration

A

Calibrate your electrode regularly

24
Q

Use of an indicator in an acid-base titration

A

To signal the end of a titration

25
Q

How the volume of gas would change when temperature was changed

A

Volume increases as temperature increases

Molecules of gas have more kinetic energy

26
Q

Percentage of mass of an element in a compound

Find percentage mass of sodium in sodium carbonate

Na2CO3

A

Na = 23

Na2CO3 = 106

23 x 2
________ x 100 = 43%

106

27
Q

Surface area to volume ratio =

A

Surface area ➗ volume

28
Q

What happens to mass in a chemical reaction

A

Mass is always conserved

29
Q

Why are there always the same number of atoms on each side of reaction equation

A

No atoms are destroyed or created

30
Q

If mass reaction may seem to change what could be a cause to this

A

Because one of the reactants is a gas found in air and all the products are solids, liquids or aqueous

31
Q

Why does mass increase if one of reactants are a gas

A

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
Q

Why might mass decrease in a chemical reaction

A

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
Q

Why might mass seem to decrease in chemical reaction

A

One of products is a gas and all the reactants are solids, liquids or aqueous

34
Q

When does a chemical reaction stop

A

When one of reactants is used up

Any others are in excess

35
Q

What is amount of product formed directly proportional to

A

Amount of limiting reactant

36
Q

How much volume does 1 mole of any gas occupy at 20°C

A

24dm3

20°C = atm = at room temperature

37
Q

Volume of gas =

A

Mass of gas
______________ x 24

Mr of gas

38
Q

Mr =

A

Relative formula mass

39
Q

r.t.p

A

Room temperature and pressure

40
Q

What’s the volume of 319.5 g of chlorine at r.t.p?

A

319.5
________ x 24 = 108dm3

71 (Cl2)

41
Q

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

A

Because chlorine naturally exists as a diatomic molecule in its gaseous form

So need 2 chlorine atoms

42
Q

Elements that naturally exist as diatomic molecules in their gaseous form

A

Bromine
Iodine
Nitrogen

Chlorine

Hydrogen
Oxygen
Fluorine

43
Q

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?

A

30 ➗ 0.2 = 150g/dm3

44
Q

What’s the concentration, in mol/am?, of a solution with 2 moles of salt in 500 cm?

A

Convert cm3 to dm3 by ➗1000

500 ➗ 1000 = 0.5dm3

2 ➗ 0.5 = 4mol/dm3

45
Q

Titration

A

Experiments that let you find the volumes needed for 2 solutions to react together completely

46
Q

What does 0% percentage yield mean

A

No reactants were converted into product so no products was made

47
Q

What does 100% percentage yield mean

A

You got all ghe product you expected to get

48
Q

What are 3 common reasons some produtpct or reactant gets lost along the way

A

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
Q

Why can yield never be 100% in reversible reactions

A

The products can turn back into reactants

50
Q

How could there be side reactions

A

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
Q

Mole

A

23
Mass of a substance that contains 6.02 x 10
particles

Chemistry (10 decks)

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