1.3 Chemical Calculations

How can we calculate the number of protons, electrons and neutrons in an atom?

PEN

Protons and electrons are the same number as the bottom number

Neutrons are top number - bottom number

Isotope

atoms of the same element with the same number of protons but different number of neutrons

What is used as the standard measurement of relative mass

Carbon 12

Every atomic mass is compared to ___ mass of a carbon 12 atom

1/12

Relative Isotopic Mass

mass of an atom of an isotope compared to 1/12th the mass of a carbon 12 atom

Relative atomic mass

the weighted mean mass of an atom, relative to 1/12th. The mass of one atom of Carbon 12 o

How can we calculate RAM (Relative atomic mass )

(Mass of %) + (Mass of %) / 100

What is the RAM of

35Cl - 75%

37Cl - 25%

(35 × 75) + (37 × 25) / 100

Mass spectrometer

allows us to analyse samples of isotopes and determine their relative abundance

What are the five steps of mass spec

Vaporisation, Ionisation, Acceleration, Deflection, Detection

Vapourisation

sample must be a gas

Ionisation

Electron gun knocks off the outer shell and forms positive ions

Acceleration

Positively charged plates repel the ions accelerating them

Deflection

This takes place depending on their mass/charge ratio, the electromagnetic can be adjusted

Detection

Current values are tgen used in combination with the flight times to produce a spectra print out with the relative abundance of each isotope displayed

Only a very ______ sample is required and is used for ___ tests, or at ____ _______

small

drug

crime

scene

Moles

amount of any substance that contains the same number of particles as there are atoms in exactly 12g of Carbon 12

Moles

Mass/ Mr

Empirical Formula

the simplest whole number ratio of atoms in each element present

Molecular Formula

actual number of atoms of each element in a compound/ molecule

Formula for molecular

Empirical Formula x Mr / Mr of empirical formula

Avogadro’s hypothesis

Equal volumes of gases at the same temperature and pressure contain equal number of molecules

Standard Conditions

298K or 25C

101 kPA or one atmosphere

What is the value for absolute zero?

-273K where nothing moves

Moles equation - Volume dm³

n= V/24.5

Moles equation - cm³

n= V/24500

What happens to the volume of a gas when the pressure is increased?

Decreases

What happens to the volume of a gas when the temperature increases

Increases

In pV=nRT

what is P?

What is V?

What is n?

What is T?

What is R?

Pressure Pa

Volume m³

Number of moles

Temperature K

Gas constant

Moles equation

Vol x conc / 1000

Equation for concentration?

moles x 1000/ vol

Percentage Yield

Actual amount in mol of products / theoretical amount in mol of products x 100

Equation for atom economy

Mr of desired products/ Mr of total reactants x 100

A reaction may have a high percentage yield but a ______ percentage atom economy

low

Benefits of a high atom economy?

Less waste therefore less going to landfill

Saves money as less costs for the chemical industry to deal with waste

Less chance of hazardous/toxic by products

Procedural errors

due to the procedure itself such as not mixing a solution properly

Precision errors

due to accuracy within the apparatus

Uncertainty

half of the smallest reading

Equation for percentage error

Error/ Reading x 100

The _________ the uncertainty the more precise your measurements

smaller