3.1.2 Amount Of Substance Flashcards
Write the formulas for the following common ions:
Silver
Zinc
Ammonium
Hydrogen
Nitrate
Sulphate
Carbonate
Hydrogencarbonate
Hydroxide
Hydride
Phosphate
Silver - Ag+
Zinc - Zn2+
Ammonium - (NH4)+
Hydrogen - H+
Nitrate - (NO3)-
Sulphate - (SO4)2-
Carbonate - (CO3)2-
Hydrogencarbonate - (HCO3)-
Hydroxide - OH-
Hydride - H-
Phosphate - (PO4)3-
How do we write chemical formulae?
Ensure that the charges on both ions are balanced, and therefore equal and opposite.
Eg. Barium Hydroxide
Ba2+ = 2+ charge and OH- = 1- charge
Ba(OH)2
What is the meaning of the ending ‘ate’?
Contains oxygen
Eg. Sulphate, carbonate, phosphate etc..
General equation for a substance reacting with oxygen?
Substance + oxygen -> oxides
General equation for reaction between metal and water?
Metal + water -> metal hydroxide + hydrogen
General equation for reaction between metal and acid?
Metal + acid -> salt + hydrogen
General equation for reaction between a hydrogencarbonate and acid?
Hydrogencarbonate + acid -> salt + water + carbon dioxide
General equation for the reaction between ammonia and acid?
Ammonia + acid -> ammonium salt
General equation for the thermal decomposition of a metal carbonate?
Metal carbonate -> metal oxide + carbon dioxide
General equation for reaction between metal oxide and acid?
Acid + metal oxide -> salt + water
General equation for reaction between metal hydroxide and acid?
Acid + metal hydroxide -> salt + water
General equation for the reaction between metal carbonate and acid?
Acid + metal carbonate -> salt + water + carbon dioxide
What is a salt?
When the hydrogen ion in an acid is replaced by a metal, it is a salt
-the first part of the salt is from the metal, and the second part is from the acid
-have the names: chloride, sulphate, nitrate and phosphate
How do you know when an equation is balanced?
The equation is balanced when there are the same number of each atom in the reactants, and in the products.
Define relative atomic mass?
The relative atomic mass is the average mass of one atom of an element, compared to one twelfth of the mass of an atom of carbon-12.
Ar = average mass of one atom of an element / 1/12th of the mass of an atom of carbon-12
How is the relative atomic mass of an element calculated?
-from the average mass of the isotopes of an element, weighted to their abundance
Ar = (% abundance 1 x mass 1) + (% abundance 2 x mass 2) etc… / 100
-these values are shown on the periodic table
Define relative molecular mass?
The relative molecular mass is the average mass of one molecule, compared to one twelfth of the mass of an atom of carbon-12.
Mr = average mass of one molecule / 1/12th mass of an atom of carbon-12
What is a molecule?
When there is a set number of atoms, in a set ratio.
What is the relative formula mass?
It is the relative mass used for ionic compounds, and is calculated in the same way as the Mr.
How is the Mr of a molecule found using Ar values?
By adding up the relative atomic masses of all of the atoms present in one molecule.
Eg. CO2 = 12 + (16x2) = 44
What is Avogadro’s constant?
The Avogadro’s constant is the number of particles in one mole of any substance
What is the value of Avogadro’s constant?
6.022 x 10^23
What is a mole?
A mole is an amount of a substance that contains 6.022 x 10^23 particles.
-the Ar or Mr of any atom or molecule will contain 6.022 x 10^23 individual atoms or molecules
-therefore, the Ar of an element is equal to the mass of one mole of its atoms in grams
Eg. Carbon
Ar = 12
Mass of 1 mole of carbon atoms = 12
What is the equation linking mass, mr and moles?
Moles = mass/Mr
Or
Mass = Mr x moles
(Mass is measured in grams)
What is a solvent?
The liquid in which the solute is dissolved to make a solution.
What is a solute?
The substance that is dissolved in the solvent to make a solution. It can be a solid, liquid or a gas.
What is a solution?
A solution is the substance formed when a solute has dissolved in a solvent.
What is concentration?
Concentration of a solution refers to the amount of solute dissolved in a known volume of a solvent (usually in moldm-3 or gdm-3)
How is concentration calculated?
Concentration = number of moles/volume
What is the difference between a concentrated and dilute solution?
A concentrated solution has a high concentration of solute but a dilute solution has a low concentration of solute.
How many cm3 are in 1 dm3?
1000
How do you convert from cm to dm?
X1000
How do you convert from moles to grams?
divide by the Mr
How do you calculate concentration from number of moles and volume?
Concentration = number of moles / volume
What is a titration?
A method used to find the concentration of a solution, when one of the reagents is a standard solution.
What is a standard solution?
A solution of which the exact concentration is known, so if a precise volume of it is measured, the number of moles can be calculated.
What do we assume all gases behave like for calculations?
An ideal gas
What do we assume all gases behave like for calculations?
An ideal gas
How does an ideal gas behave?
Gas molecules are moving fast and randomly
Gas molecules do not attract or repel each other (no intermolecular forces)
The size of the particles is negligible
What is the ideal gas equation?
PV = nRT
P=pressure in pascals
V=volume in m3
n=number of moles
R=molar gas constant - 8.31
T=temperature in Kelvin
What is kelvin and how does it work?
Kelvin is another scale of temperature
0K = absolute zero, when particles have no kinetic energy
273K = 0*c
*c + 273 = K
How do you covert from dm3 to m3?
X 1000
What are the standard conditions?
293K
100,000 Pa
1 mole of a gas under standard conditions occupies 24.3cm3.
Define molecular formula
The actual number of each type of atom present in one molecule of the compound.
Define empirical formula
The simplest whole number ratio of the atoms present in one molecule of a compound.
What are the steps needed to calculate empirical formula?
Divide mass by Ar to calculate moles
Divide by the smallest moles to calculate mole ratio
Multiply to find the whole number ratio
What is combustion analysis?
A method of determining the empirical formula
A sample of an unknown compound is burned in an excess of oxygen, and the products of combustion are analysed.
It is used for organic compounds.
What are the 4 steps in a combustion analysis calculation?
- Mass of carbon
- Mass of hydrogen
- Mass of oxygen
- Calculate empirical formula
Define anhydrous
An anhydrous substance is one that does not contain water.
Define water of crystallisation
Water of crystallisation is water which is locked into a crystal in a fixed way.
Define hydrated substance
A substance is hydrated if water, or the elects of water (hydrogen and oxygen in a 2:1 ratio) is added to it.
What is percentage atom economy?
It is a method of calculating what percentage of the reactants should theoretically be converted into useful products in a reaction.
This measures the amount of waste produced and therefore the success of the reaction.
What does it mean if a reaction has a high atom economy?
Mostly converted into useful product
If there is only one product, the atom economy is always 100%
What is the equation to calculate percentage atom economy?
(Mr of useful product / total Mr of reactants) x 100
What is percentage yield?
It gives information on the practical efficiency of a reaction, as no reactions ever produce a 100% yield.
Why is a 100% yield never produced?
The reaction does not go to completion
Unwanted side reactions occur
The reaction is reversible
What is the formula to calculate percentage yield?
(Mass of specific product formed / theoretical mass that could be formed) x 100
